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Biogeochemical Cycling

Direct Analysis of Marine Dissolved Organic Matter Using LC-FT-ICR MS
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  • Oliver J. Lechtenfeld*
    Oliver J. Lechtenfeld
    Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany
    ProVIS−Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany
    *Email: [email protected]
    More by Oliver J. Lechtenfeld
    Orcidhttps://orcid.org/0000-0001-5313-6014
  • Jan Kaesler
    Jan Kaesler
    Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany
    More by Jan Kaesler
  • Elaine K. Jennings
    Elaine K. Jennings
    Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany
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    Orcidhttps://orcid.org/0000-0003-4508-0190
  • Boris P. Koch*
    Boris P. Koch
    Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany
    University of Applied Sciences, An der Karlstadt 8, 27568 Bremerhaven, Germany
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-8453-731X
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Environmental Science & Technology

Cite this: Environ. Sci. Technol. 2024, 58, 10, 4637–4647
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https://doi.org/10.1021/acs.est.3c07219
Published March 1, 2024

Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Marine dissolved organic matter (DOM) is an important component of the global carbon cycle, yet its intricate composition and the sea salt matrix pose major challenges for chemical analysis. We introduce a direct injection, reversed-phase liquid chromatography ultrahigh resolution mass spectrometry approach to analyze marine DOM without the need for solid-phase extraction. Effective separation of salt and DOM is achieved with a large chromatographic column and an extended isocratic aqueous step. Postcolumn dilution of the sample flow with buffer-free solvents and implementing a counter gradient reduced salt buildup in the ion source and resulted in excellent repeatability. With this method, over 5,500 unique molecular formulas were detected from just 5.5 nmol carbon in 100 μL of filtered Arctic Ocean seawater. We observed a highly linear detector response for variable sample carbon concentrations and a high robustness against the salt matrix. Compared to solid-phase extracted DOM, our direct injection method demonstrated superior sensitivity for heteroatom-containing DOM. The direct analysis of seawater offers fast and simple sample preparation and avoids fractionation introduced by extraction. The method facilitates studies in environments, where only minimal sample volume is available e.g. in marine sediment pore water, ice cores, or permafrost soil solution. The small volume requirement also supports higher spatial (e.g., in soils) or temporal sample resolution (e.g., in culture experiments). Chromatographic separation adds further chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes.

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Synopsis

This article describes how effective salt separation revolutionizes DOM analysis in original seawater and improves accurate characterization of marine biogeochemistry.

Introduction

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Marine dissolved organic matter (DOM) constitutes a large active pool in the global carbon cycle (662 petagrams of carbon). (1) DOM is among the most complex chemical mixtures on our planet posing the greatest challenges to even the most advanced analytical methods targeting comprehensive chemical characterization and structural elucidation. Due to its unrivaled sensitivity and molecular resolution, ultrahigh resolution mass spectrometry has greatly advanced our understanding of the chemical composition and complexity of DOM. Each individual measurement reveals thousands of mass peaks, for which molecular formulas (MFs) can be assigned and, together with their respective intensities, are commonly exploited for DOM source and process studies. (2−5)
Analyzing marine DOM by mass spectrometry is impaired by the fact that the concentration of salts in the ocean exceeds the concentration of DOM by a factor of ∼35,000. Inorganic ions carry most of the charge in electrospray ionization (ESI), thus suppressing ionization of organic molecules. Consequently, the quantitative direct analysis of saltwater samples with ESI mass spectrometry has not been possible until now. DOM concentrations (measured as the proportion of dissolved organic carbon; DOC) of 40 μmol DOC L–1 and below (1) pose an additional challenge in terms of instrument sensitivity.
Previous approaches of separating the sea salt and enriching the marine DOM to improve analytical sensitivity and robustness often used solid-phase extraction (SPE). However, SPE using a state-of-the art divinylbenzene-based polymer (PPL) only yields approximately 40–60% of the DOC from seawater, (6,7) and the chemical composition of the extracts is strongly influenced by the chemistry of the adsorbant, (8,9) the loading of the column, (8,10) and the volume and type of eluent. (11) In study areas with highly variable contributions of different DOM sources (e.g., estuaries, phytoplankton blooms), (12,13) matrix-effects during solid-phase extraction represent an additional challenge for data interpretation. (14,15)
Liquid chromatography-mass spectrometry (LC-MS) using ultrahigh resolution mass spectrometers is increasingly applied to natural organic matter and petroleum samples to improve the physicochemical understanding by determining polarity and size distribution. (16−22) However, major questions remain with regard to the representativeness of extracts. (23−25) Due to the variable and largely unknown extraction efficiency of individual DOM compounds, it is difficult if not impossible, to quantitatively relate the molecular composition of extracts to the composition of DOM in original samples hampering our understanding of marine biogeochemical cycles.
From these challenges, several key requirements emerge for improving DOM analysis in seawater:
(i)

Simplifying marine DOM sample preparation by removing the need for sample extraction.

(ii)

Improving the representativeness of marine DOM composition as seen by FT-ICR MS.

(iii)

Improving comparability of the analytical results with other bulk and molecular-level chemical techniques.

(iv)

Leveraging the quantitative potential of nontargeted mass spectrometric analysis of complex DOM.

Such advancements would require to analyze non-extracted seawater samples - a method that is not yet available.
Here we present a new method for DOM characterization, which allows direct injection of original (i.e., non-extracted), filtered ocean water samples at native salt and DOC concentrations. To achieve this, we used reversed-phase liquid chromatography, enhanced by an isocratic elution step and a postcolumn counter gradient, hyphenated with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS). The method is tested with DOM samples of varying carbon and salt concentrations from the Central Arctic Ocean and peat pore water. We evaluated the linearity of mass peak magnitudes for variable DOC concentrations, repeatability and intermediate precision, robustness against salt matrix and changing sample pH, and compared the results with traditional analysis of seawater DOM SPE extracts.

Methods

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Samples and Chemicals

Seawater samples AOlow (55 μmol DOC L–1) and AOhigh (88 μmol DOC L–1) were collected in surface water of the central Arctic Ocean during RV Polarstern cruise PS122/3 in spring 2020 (Table SI 1). One liter of seawater was filtered through precombusted glass fiber filters (500 °C, 5 h, Whatman, GF/F, approximately 0.7 μm nominal pore size), and aliquotes of the samples were immediately frozen at −20 °C until analysis. Original seawater samples were thawed and filtered again immediately before analysis (0.2 μm, Minisart RC4, Sartorius, Goettingen, Germany) to remove any particles that may have formed after melting the samples.
500 mL of the filtered sample AOhigh was acidified to pH 3 (HCl, ultrapure; Merck) and extracted on board using a standard method (6) (Bond Elut PPL, 200 mg, Agilent). DOM was eluted with 2 mL of MeOH (HPLC grade, Merck) and stored at −20 °C to minimize esterification. (26) The carbon-based extraction efficiency was ∼40%, comparable to other marine waters. (7,27) The extract was diluted (via evaporation of MeOH and reconstitution in ultrapure water using ultrasonication) to the same concentration as the original sample (AOhighSPE: 88 μmol DOC L–1) immediately prior LC injections.
A peat pore water (PPW) sample was collected from the Neustädter Moor (Lower Saxony, Germany). (28) The sample was diluted with ultrapure water (Milli-Q Integral 5, Merck, Darmstadt, Germany) to match marine DOC concentrations (PPWS0; 20–160 μmol DOC L–1). NaCl (p.a. Merck, baked at 400 °C for 4 h) was added to simulate salt concentrations of a seawater (salinity: 35; PPWS35), an estuarine (salinity: 17; PPWS17), and a sea ice brine sample (salinity: 70; PPWS70). These salt amended PPW-DOM samples were used for method validation (for an overview and complete list of samples used in this study, cf. Table SI 2, Figure SI 1).
For instrument quality control, 10 mg L–1 Suwannee River Fulvic Acid standard (SRFA, 2S101H, International Humic Substances Society) spiked with a set of previously used model compounds (Table SI 3) was used. (23,28)

Reversed-Phase Liquid Chromatography

A recent reversed-phased liquid chromatography (RPLC) method for the direct injection of water samples (25,28) was modified to account for the very high salt concentration in seawater. The system consisted of an ultrahigh pressure chromatography system (UltiMate 3000RS, Thermo Fischer Scientific, Waltham, U.S.A.), equipped with a binary high-pressure pump (HPG-3200RS), an auxiliary quaternary low pressure gradient pump (LPG-3400SD), an autosampler (WPS-3000TRS), a column oven (TCC-3000RS), and a diode array detector (DAD-3000RS). DOM separation was performed with a polar end-capped C-18 reversed-phase column (ACQUITY HSS T3, 1.8 μm, 100 Å, 150 × 3 mm, Waters, Milford, U.S.A.) equipped with a guard column (ACQUITY UPLC HSS T3 VanGuard, 100 Å, 1.8 μm, 2.1 mm × 5 mm), at a column temperature of 30 °C. As mobile phases, ultrapure water (adjusted with 0.1% formic acid and ammonium hydroxide (NH4OH) to reach pH 3) and methanol (LC-MS-grade, Biosolve, Valkenswaard, Netherlands, with same amounts of formic acid and NH4OH) were used. The flow rate was set to 0.2 mL min–1. The same mobile phases and flow rate were used for the auxiliary pump but without modifiers. A mobile phase gradient (isocratic step with 100% ultrapure water for 3.5 min and linear increase to 100% MeOH within 14 min, then hold 100% MeOH for 9 min) was used. The auxiliary pump mirrored the gradient of the main pump with an additional delay of 4.5 min to account for the flow path differences between both pumps and the T-piece, which was installed after the LC column.
An adjustable flow splitter (QuickSplit #600-PO10–04, ASI, Richmond, CA, U.S.A.) was installed after the T-piece, and the combined flow (0.4 mL min–1) was divided between the DAD (0.3 mL min–1) and the MS (0.1 mL min–1). The time difference between both detectors was approximately 0.5 min. Immediately before the MS, a 2-way-6-port valve was programmed to divert the flow to waste during the time when most of the salt eluted from the column (switch to ESI at 10.5 min). The void volume of the system was approximately 0.9 mL (4.3 min), and the methanol from the gradient of the main pump first reached the MS after approximately 13 min. For the salt-free PPW and the PPL-extracted seawater samples, the 2-way-6-port valve was already switched at 5.5 min to record MS spectra for the early eluting DOM compounds (Figure SI 2).
An injection volume of 100 μL was used for all samples. The effect of sample pH on the separation was tested by adjusting sample AOlow to pH 3 with formic acid (AOlowpH3, Table SI 2, Figure SI 1). With respect to carbon concentration, the seawater samples were not adjusted prior to injection in order to ensure a consistent matrix across samples.

ESI-FT-ICR Mass Spectrometry

Mass spectra were obtained with an FT-ICR mass spectrometer equipped with a dynamically harmonized analyzer cell (solariX XR, Bruker Daltonics, Billerica, U.S.A.) and a 12 T refrigerated, actively shielded superconducting magnet (Bruker Biospin, Wissembourg, France). The data were acquired in negative ion mode with an ESI source (Apollo II, Bruker Daltonics, Billerica, U.S.A., capillary voltage: 4.3 kV) in full profile magnitude mode with a transient size of 4 MWord (∼1.6 s free induction decay, FID). The ion accumulation time (IAT) was set to 1.6 s, and the mass range was set to m/z 147–1000. The mass resolving power (m/Δm, full width half-maximum) at m/z 400 was approximately 500,000 ± 40,000, which is sufficient to resolve all major DOM ions in the considered mass range. SRFA spiked with model compounds was measured with 0.5 s IAT (cf. SI Text: Instrument Quality Control).
As reference to state-of-the art analysis, the PPL extracted seawater sample (AOhighSPE) was diluted to 0.8 mmol DOC L–1 (10 mg DOC L–1) in ultrapure water and MeOH (50/50, v/v) and measured with the standard direct infusion (DI-) FT-ICR MS method (256 scans, 4 MWord, 8 ms IAT, ESI(−), 4 μL min–1).

Data Processing

Segmentation of LC-FT-ICR MS Spectra

Seawater DOM elution profiles in the retention time range from 13 to 25 min did not show distinguishable chromatographic features (Figure 1). LC-FT-ICR MS-derived single scan full profile spectra were therefore binned into 1 min segments using a custom script in DataAnalysis (Version 6, Bruker, cf. SI Script for DataAnalysis; start: 13.5 min, end: 24.5 min), resulting in 11 segments. In the last two segments (22.5–24.5 min) only the PPL extracted sample showed typical DOM spectra, and these segments were not evaluated for the original seawater samples. For the tests with PPW and the PPL-extracted seawater samples, seven segments for the early eluting DOM (6.5–13.5 min) were additionally included due to the earlier valve switching. For the seawater samples, these segments were not available due to the valve setting, directing the flow to waste during the initial elution of salt (Figure SI 2). Segment-wise retention times (RT) are reported using the mean RT of the respective segment (e.g., 14 min for the segment 13.5–14.5 min).

Calibration and Molecular Formula Assignment

Averaged LC-FT-ICR MS and DI spectra were internally recalibrated with a list of known DOM masses (n = 425; 150 < m/z < 980), resulting in an average root-mean-squared error of 0.15 ppm across segments and samples (n = 165). Molecular formulas (MFs) were assigned in the mass range 150–1000 Da with a maximum tolerated mass error of ±0.5 ppm and element ranges C:1–60, H:1–122, O:0–40, N:0–2, S:0–1 using an in-house software. We also considered Na for samples PPWS0 and PPWS35. Tentative Na-adducts ([M – 2H+ + Na+]−) for highly polar DOM molecules were identified by linking a molecular formula (CcHhNnOoSs) to its potential Na-adduct (CcHh-1Na1NnOoSs). To distinguish between MFs assigned to DI-FT-ICR MS and LC-FT-ICR MS data, we refer to molecular features as molecular formulas detected at a given retention time (here: in a distinct segment).

Blank Correction

Pure water injections were measured in triplicates across the sample sequence and processed in the same way as the samples. The MFs in the individual blank segments were subtracted from the list of MFs of the respective segments of the sample. Subtraction was based on the presence of a molecular formula in any of the three pure water injections. A full method blank was not included, but we additionally excluded MFs commonly found as contaminants in DOM samples (29) (cf. SI List of Surfactants). For the DI measurement, an instrument blank was subtracted accordingly.

Data Visualization

To visualize chromatographic performance, total ion chromatograms (TIC, summed magnitude of all detected mass peaks in each mass spectrum), total assigned ion chromatograms (TAC, summed magnitude of all mass peaks with molecular formula assignment in each mass spectrum), (19) and extracted ion chromatograms (EIC) were used. Chromatogram data were smoothed by Savitzky-Golay with 4 (TIC, TAC) and 11 (EIC) points and 1 cycle in DataAnalysis. Individual MFs and aggregated molecular descriptors (e.g., intensity weighted average H/C and O/C ratios) were plotted in the chemical H/C-vs-O/C or H/C-vs-mass space to visualize compositional differences. (30) Molecular formula based biogeochemical indices reported for marine DOM (IDEG, (31) IOS, (4) ITerr, t-Peaks (32)) were calculated, and the EICs were extracted from LC-FT-ICR MS chromatograms.
For an overview of the data processing pipeline used in this study, refer to Figure SI 3.

Method Assessment

We assessed the performance and robustness of the method according to the following criteria:
(i)

Linear detector response and sensitivity: PPW was injected at different concentrations (20, 40, 80, 160 μmol DOC L–1) covering the typical seawater DOC concentration range (PPWS0 samples) and measured with LC-FT-ICR MS. The number of assigned MFs and the total assigned intensity (i.e., sum of intensity of all peaks having a formula assignment) and a linear regression between DOC concentration and total/individual MFs intensity was used to evaluate the detector sensitivity and linearity, respectively.

(ii)

Robustness: The effect of salt on the DOM mass spectra from LC-FT-ICR MS was assessed in two ways: First, 35 g L–1 NaCl was added to the PPW samples (PPWS35 samples) prepared at different concentrations (40, 80, 160 μmol DOC L–1) to evaluate the potential masking of polar DOM molecules due to coelution of salt and compared the detector response of original and salt amended PPW. Second, we checked for potential adducts from residual salt in the PPWS35 sample and compared it to PPWS0. Finally, the effect of sample pH on the retention of polar DOM was tested by adding formic acid to sample AOlow.

(iii)

Repeatability and intermediate precision: Repeatability was determined by measuring the sample (AOlow) in triplicate with LC-FT-ICR MS, and the number of shared MFs and the coefficient of variation (CV) of raw mass peak magnitudes (hereafter: peak intensities) were evaluated. Intermediate precision was assessed using the CV of peak areas of model compounds for 11 injections during a multiday measurement.

(iv)

Comparison with PPL extracts. The PPL extracted sample (AOhighSPE) was measured with LC-FT-ICR MS (diluted to the same concentration as the original sample, 88 μmol DOC L–1) and DI-FT-ICR MS (diluted to 10 mg DOC L–1/0.8 mmol DOC L–1) and compared to the original sample (AOhigh) measured with LC-FT-ICR MS (Table SI 2). The relative difference of the peak intensities was evaluated to test the effect of extraction on the observable molecular composition. Further, an intensity averaged pseudo-DI measurement was calculated from the LC-FT-ICR MS segments. MFs solely detected in one sample and those shared between the three samples were evaluated based on their number and molecular descriptors.

More details about the validation steps can be found in SI Text: Method Assessment and Table SI 2.

Results and Discussion

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Chemodiversity and Polarity of Marine DOM from Original Seawater Samples

Our LC-FT-ICR MS method allowed the direct injection of 100 μL of filtered seawater resulting in more than 200 single DOM mass spectra at a mass resolving power of ∼500,000 at m/z 400. The marine DOM eluted from the column in a broad, unstructured peak between 13 and 25 min (Figure 1), as observed previously for aquatic DOM extracts. (23,28,33−35) Owing to the very low amount of injected DOM and long accumulation times (here: 1.6 s), the total ion chromatogram (TIC) showed a less pronounced DOM peak as compared to previous studies using concentrated DOM extracts. (23,36) However, DOM sample TICs were clearly distinguishable from blank injections (Figure SI 4), and the total assigned ion chromatograms (TAC) clearly showed the DOM elution profile (Figure 1). Compared to a peak width of individual model compounds of less than 0.5 min (full-width half-maximum (FWHM), cf. Table SI 3), peak widths of DOM m/z ratios were much wider (4–5 min FWHM, Figure 1), reflecting the large structural diversity of DOM. (35) At the level of individual m/z ratios, the retention and separation of DOM indicated that the method is suitable for low concentrated seawater samples at native concentration as well as for extracted seawater or freshwater samples (Figure SI 5). However, the low concentration of DOM in ocean water required a longer IAT to collect enough ions for detection in the ICR cell. The FT-ICR MS transient length was also extended (4 MWord, ∼1.6 s with start at m/z 147) to maximize sensitivity, resolution, and MS duty cycle. The resulting loss of time resolution as compared to our previous method (28) using 2 MWord transients on the same 12 T FT-ICR instrument did not result in a substantial loss of chromatographic resolution (Tables SI 3,4, Figure SI 6).

Figure 1

Figure 1. Total assigned ion chromatograms (TAC, solid lines, right y-axis) and extracted ion chromatograms (EIC, dashed lines, left y-axis) for two Arctic Ocean samples (AOhigh (red) and AOlow (black)) and a pure water blank injection (BLK, gray). Two m/z values on the same nominal mass were selected, representing molecular formulas with higher O/C (m/z 353.0878: C16H18O9) and lower O/C ratios (m/z 353.1606: C18H26O7). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). 100% methanol was reached at 27 min (red marker). The color bars indicate the LC retention time segments, highlighted in subsequent figures. TAC represents 35% of the TIC in this example.

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Both Arctic seawater samples resulted in a comparable summed intensity and number of detected molecular features (AOhigh: total features: 16,800, unique MFs: 5,800; AOlow: total features: 16,250, unique MFs: 5,700) with the largest number of detected MFs eluting between 15 and 19 min (Figure 2a). H/Cwa increased and O/Cwa decreased with retention time (Figure SI 7), confirming the general connection between the mean O/C ratio and polarity (number of acidic groups) of marine DOM. (23,33) Notably, all chromatographic segments showed a higher H/Cwa and lower O/Cwa ratio for seawater compared to peat pore water (Figure SI 7), which also is in agreement with previous DI (3) and LC measurements (23) of solid-phase extracted DOM. In addition, we found that the average molecular mass increased with retention time from m/z 400 at 14 min to m/z 478 at 24 min (Figures SI 7).
Direct injection and polarity separation of marine DOM also allow for novel insights into biogeochemical indices and marker MFs. Those MFs that constitute the degradation index (31) (IDEG) eluted with the majority of the DOM (15–22 min, Figure SI 12) and the broad distribution are evidence that the formulas represent a multitude of structural isomers. Only a small shift in polarity could be observed between the IDEG-POS (MFs decreasing in intensity with radiocarbon age of marine DOM) and IDEG-NEG (MFs increasing in intensity) formulas, despite clear differences based on their molecular H/C ratios. (31) In contrast, MFs from the terrestrial index (ITerr) showed a pronounced maximum of highly polar isomers related to the terrestrial markers (Terr; MFs with increased intensity in riverine DOM, Figure SI 13). (32) This confirms previous observations (based on extracted samples) that terrestrial DOM can be distinguished by molecular descriptors and polarity. (23) Although the isomeric overlap is still substantial, markers for marine (e.g., IOS-MFs) (4) and terrestrial DOM (e.g., t-Peaks) (32) cover distinct polarity regions in the LC chromatograms (Figure SI 14), providing new opportunities to resolve the compositional overlap of terrestrial and marine DOM.

Enabling Direct Seawater DOM Analysis with LC-FT-ICR MS

Severe interferences due to the salt matrix have previously hampered the direct ESI-MS analysis of marine or other salt containing samples. We achieved an effective separation of salt from most of the DOM using a comparably large chromatographic column (providing a large pore volume) and an extended isocratic aqueous step after injection as compared to our previous work (Figure SI 2). (25,28) Together, this resulted in a delayed DOM elution (main part of DOM elution > 13 min), while the salt passed the column with only little interaction with the stationary phase (Figure SI 15). Dilution of the sample with buffer free solvents via the auxiliary pump and a valve to direct the salt-containing flow to waste were important method adjustments to reduce salt-buildup inside the ESI source and on the cones, which otherwise limit the sensitivity and contribute to adduct formation during ionization. Overall, this resulted in a robust chromatography and stable mass peak intensities for long sample sequences (Tables SI 3,4; Figures SI 6,16). The counter gradient stabilized the solvent composition for ESI and reduced suppression effects from the buffered mobile phases of the primary pump. (28,37) The counter gradient also allowed the postcolumn addition of an internal standard that can assist with lock-mass calibration and baseline drift correction. (38)
To demonstrate the suitability of the method for original seawater, we assessed which MFs were not accessible because they coeluted with the salt before 13 min and whether the salt affected segments after 13 min retention time. For this purpose, we added 35 g L–1 NaCl to PPW (i.e., PPWS35) having different concentrations (40, 80, 160 μmol DOC L–1) and compared the results with salt-free PPWS0 samples (Table SI 2, Figure SI 1). Expectedly, the presence of salt prevented the detection of the most polar DOM fraction (6–13 min; 18–20% of the total assigned intensity, Figures SI 17,18). However, the impact of salt was only small for DOM eluting at 14–16 min and negligible for retention times > 16 min (Figure SI 19). In the segments at 14–16 min, the salt primarily suppressed polar MFs (Figure 3a) resulting in a small shift to higher average H/C and lower O/C ratios, compared to the same concentration of salt-free PPW (Figure 3b). Although the majority of free salt eluted already in the column void volume (Figure SI 15, cf. SI Figure 10 in Jennings et al. (2022)), part of the oxygen-rich, polar DOM may have formed Na-adducts ([M – 2H+ + Na+]−) that were partially retained on the LC column (Figure SI 20). The Na-adducts usually remain undetected, if not explicitly accounted for during formula assignment for ESI(−) MS data. Notably, this effect was slightly higher for higher PPW concentrations (Figure SI 21).

Figure 2

Figure 2. LC-FT-ICR MS analysis of original seawater samples. (a) Summed intensity of assigned molecular formulas (MFs) based on formula classes (colors in legend) for the AOlow sample over all 11 LC segments (14–24 min). Colors on the retention time axis relate to labels displayed in (b). (b) Intensity-weighted average molecular H/C and O/C ratios for all segments of two seawater samples measured at native concentration (AOlow: 55 μmol DOC L–1, black and AOhigh: 88 μmol DOC L–1, red) with LC-FT-ICR MS. Note that the segment at 24 min (lighter colors) only contained very few MFs (AOlow: 100, AOhigh: 174). For details for sample AOlow, AOhigh and AOhighSPE, cf. Figures SI 8–11.

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Figure 3

Figure 3. Effect of salt on the peak intensities of original peat pore water (PPW) measured by LC-FT-ICR MS. (a) Distribution of relative differences between peak intensities (δRAW) of molecular formulas (MFs) detected without (PPWS0) and with salt (PPWS35; 35 g L–1 NaCl) injected at 80 μmol DOC L–1 for individual LC-segments (14–22 min, # MFs: 105 < n < 1937; with 25th, median, and 75th percentile as white lines). The dashed lines indicate the peak intensity repeatability limits (cf. Figure SI 25). (b) Intensity-weighted average molecular H/C and O/C ratios for all segments between 14 and 22 min for PPW at 80 μmol DOC L–1 without (hexagons) and with salt (squares). Transparent symbols indicate segments < 14 min and > 22 min.

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Analysis of Samples at Native DOM Concentrations

Linear Detector Response

We tested how the peak intensities of MFs at a given retention time segment corresponded to the amount of DOC injected. For this purpose, salt-free PPWS0 was diluted to concentrations covering typical seawater DOC concentrations (20, 40, 80, and 160 μmol DOC L–1; equivalent to 2–16 nmol DOC injected, Figure SI 1). Based on MFs that were detected at all four concentration levels in a given retention time segment ≥ 14 min (# MFs: 75 < n < 814), 63% (at 21 min) to 86% (at 16 min) of the respective mass peak magnitudes showed a highly significant (p < 0.01) linear relationship with DOC concentration (Figure 4). Deviation from the linearity was related to peaks with lower magnitude or LC-derived contaminants (Figure SI 22).

Figure 4

Figure 4. Linearity of detector response. (a) Summed intensity of assigned molecular formulas (MFs; total assigned intensity) in individual LC-segments (7–24 min, 18 segments) of different concentrations (20–160 μmol DOC L–1) of salt-free peat pore water (PPWS0). Without salt addition, DOM in early segments (<13 min) can be observed, which was otherwise masked by the coelution of the salt matrix (cf. Figure SI 23) and the respective time of valve switching (green marker). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). The gray box on the retention time axis indicates data displayed in (b). (b) Linear regression of peak intensities for MFs detected in segments of the PPWS0. MF with R2 values > 0.98 (corresponding to a significant linear regression at α = 0.01) are shown, representing 63% (21 min)–86% (16 min) of MFs that were detected at all concentrations (75 < n < 814; with 25th, median, and 75th percentile as white lines). Segments < 13 min and > 21 min were omitted due to the low number of detected MFs for the 20 μmol DOC L–1.

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Consequently, within each retention time segment, total assigned intensity (Figure 4a) and the number of MFs linearly increased with DOC concentration (Figure SI 17). Notably, a higher DOC concentration is likely to result in more MFs being detected, affecting the apparent molecular composition and requiring adjustments in data processing. However, if only shared MFs are considered, the aggregated molecular descriptors O/Cwa and H/Cwa of all segments in the PPW dilution series were highly similar, confirming that the molecular composition is largely conserved independent of sample concentration (Figure SI 17). Therefore, our method provides a sufficient linear range to accommodate the entire range of DOC concentrations expected for typical seawater samples.
Using the salt-amended PPWS35 samples, we found that the average molecular composition was well preserved across a concentration gradient (Figures SI 18,19), similar to the salt-free assessment. The detector response was highly linear and comparable to the test without salt (Figure SI 23). Expectedly, for the most polar segments, the sensitivity decreased (flatter slopes) reflecting the intensity suppression by salt adducts. Overall, this resulted in a lower detector response (based on total assigned intensity) of the saline samples (Figure SI 24). However, removing the first three segments that were most affected by the matrix (14–16 min), an almost identical response was observed for saline and salt-free PPW (Figure SI 24). Lower (17 g L–1) and higher (70 g L–1) salt concentrations still resulted in a linear detector response, indicating that a comparison of DOM samples from a salt gradient (e.g., estuary, sea ice) is possible.
The linear response of total assigned intensity with DOC concentration (Figure SI 24) was previously not achievable with SPE-based analyses and demonstrated the potential to semiquantitatively evaluate molecular features in DOM. However, absolute quantification can of course only be achieved in targeted molecular approaches for which standards are available.

Repeatability and Intermediate Precision

Sample AOlow was measured in triplicate to explore the mass peak magnitude variance as a function of magnitude (39) and retention time. For all segments, the CVs of the peak intensities were below 10% for 60% of the MFs and below 18% for 90% of the MFs detected in the LC segments (380 < n < 1700, Figure SI 25). Similarly, between 51% (22 min) and 73% (18 min) of the MFs were detected in all three replicates, which in turn accounted for 71% to 95% of the total assigned intensity, similar to measurements of SRFA at much higher concentrations (Figure SI 26). (28) As found for previous assessments, peak detection and repeatability were primarily dependent on peak magnitude. (28,40) Using the LC-derived peak areas of the five model compounds spiked into SRFA, the method achieved 5–6% repeatability and 9–17% intermediate precision (Table SI 4).

Recommendations for Sample and Data Handling

An important advantage of our new method is that it drastically simplifies sample preparation and avoids the chemical fractionation that results from SPE. However, when working with very small volumes of saline water, it is very important to consider fractionation effects due to filtration. In our study, we still used a fairly large sample volume for filtration (1 L). When filtering minimal amounts of seawater (e.g., with syringe filters), it is important to consider that DOM can be absorbed on the filter surface. (41) We therefore recommend cleaning and conditioning the filter with sufficient sample volume to avoid chemical fractionation. In DOM analysis, it is best to freeze the sample immediately after filtration. (42,43) We do not recommend acidification with HCl, as it introduces additional inorganic ions, but acidification with formic acid to pH 3 and cooling might be an alternative option for sample storage. It is noteworthy that the peak intensity increased by 15 to 38% when samples were adjusted to pH 3 with formic acid prior to injection (Figures SI 27,28). Acidification leads to protonation of small, highly polar compounds, which can thus be better separated from the salt. The robustness of the method can be further improved for samples whose native pH values differ greatly (e.g., from an estuary) by adjusting the sample pH prior injection. We also recommend refiltration with 0.2 μm cellulose acetate filters to protect the LC from particles that may form during sample storage. Because of the highly linear relationship between sample DOC concentration and peak magnitude (Figure 4), we recommend measuring samples at their native concentration rather than adjusting DOC concentration prior to analysis, as is common with DI measurements.
Although the longer run time of LC-FT-ICR MS increases the cost of analysis compared to DI-FT-ICR MS measurements, it eliminates the time-consuming extraction step, saving time and chemicals during field campaigns.

DOM Composition from Original Water versus SPE Extracts

Effect of PPL Extraction on the Observable DOM Chemodiversity

For all segments ≥ 14 min combined, the SPE extract of AOhigh that was adjusted to 88 μmol DOC L–1 (AOhighSPE) had a 59% higher total assigned intensity compared to the original AOhigh sample at the same DOC concentration (data not shown). Also, the total number of molecular features differed, with 16,254 in the directly measured and 20,540 in the PPL extracted sample. Assuming that the bulk carbon extraction efficiency of 40% is reflected in a corresponding (average) loss of the TAC, the SPE extract in fact represents only 63% of the original seawater TAC, which is explained by the improved detection of well-ionizing polar compounds by direct LC-FT-ICR MS measurement (Figure SI 5).
Accordingly, more polar segments contained a larger number of MFs and higher peak intensities compared to the extract (Figure 5, Figure SI 8). The early segments (7–13 min) were not accessible with the new method (coelution of salt) but accounted for only ∼1% of the summed intensity and 6% of the individual MFs of the extract (Figure SI 8). However, SPE with hydrophobic resins such as PPL also results in a loss of the most polar DOM compounds. (9,25,28) The highly polar DOM fraction that could still be observed in the extract (<14 min) corresponded to 711 distinct MFs, of which one-third (n = 233) was also detected in the measurement of the original water sample (with RT ≥ 14 min). Early eluting unassigned mass peaks in the measurement of AOhighSPE probably represent chemical noise (Figure SI 29), possibly from silanol compounds derived from the chromatographic column. In contrast to the results obtained by adding salt to the PPW, the loss of intensity and number of unique MFs due to the coeluting salt in seawater samples as compared to their PPL extracts is much smaller and can be attributed to the unavoidable loss of such polar DOM compounds during the SPE process. The evaluation of specific biogeochemical markers for polar terrestrial DOM clearly demonstrated that SPE, even if combined with LC-FT-ICR MS, misses some of the most polar DOM compounds (Figures SI 13,14).

Figure 5

Figure 5. Comparison between an original (AOhigh, red) and PPL-extracted sample (AOhighSPE, blue) measured at 88 μmol DOC L–1 with LC-FT-ICR MS. (a) Summed intensity of assigned molecular formulas (total assigned intensity) in each segment (7–24 min, 18 segments). No MFs were assigned to segments < 14 min in the original sample AOhigh due to the coelution of salt and the respective time of valve switching (green marker). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). (b) Relative peak intensity difference (δRAW) of all shared MFs in original AOhigh and PPL-extracted AOhighSPE seawater. Positive values indicate higher peak intensity in the original sample. The striped part of each bar for AOhighSPE in (a) and solid line in (b) indicate the mean loss in intensity according to the bulk carbon-based extraction efficiency (40%).

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In the segments ≥ 14 min, 5,692 MFs were detected in the original sample (AOhigh), as compared to 6,607 MFs in its SPE extract AOhighSPE. Out of those, 3,951 MFs were detected in both analyses (Figures SI 30,31). Although the majority of DOM in the SPE extract eluted at distinctly larger retention time as compared to the original sample (Figure 5, Figure SI 32), we observed a consistent shift toward lower H/C values considering each segment individually (Figure SI 7). This points to an additional extraction bias at the DOM isomer level, an effect previously not observable with DI methods. Notably, the shift in molecular composition due to the elimination of extraction bias will also impact ionization during ESI(−), and the observed relative peak intensity differences (δRAW, Figure 5b) thus only reflect the change in detector response. However, the spread in δRAW values indicated that extraction efficiencies for individual DOM may be studied in the future.
The overall higher intensity and number of detected MFs in the SPE extract were mainly driven by the later eluting, less polar DOM fractions and can be attributed to the selective enrichment of nonpolar compounds on the PPL sorbent. (9) Our results agree with results from effluent samples, (25) where also a negligible contribution of polar DOM and a proportionally higher contribution of less polar DOM were found in SPE extracts, when injected at the same DOC concentration. In the PPL-extracted AOhighSPE, a higher fraction of CHO MFs (48%) was found as compared to the original sample (42%, Figure 5, Table SI 5). The comparable proportion of CHNO formulas (∼36%, Table SI 5) in the original and PPL extracted sample indicated that despite lower recovery of nitrogen-containing DOM by SPE these compounds profit from the reduced ionization suppression as compared to DI-FT-ICR MS.
We conclude that the loss of the most polar fractions due to coeluting salt is negligible compared to LC-FT-ICR MS of SPE extracts and that, in contrast, more polar compounds can be studied with the new direct injection LC-FT-ICR MS method.

Comparison of Conventional Direct Infusion and Original Water LC Analysis

The state-of-the art method to analyze the molecular composition of seawater DOM is direct infusion (DI) of extracts into FT-ICR MS. We compared DI analysis of AOhighSPE that was measured with approximately 9-fold enrichment as compared to the original sample (see Methods). While the original water LC analysis of the AOhigh sample only used 8.8 nmol C and covered 204 LC scans, distributed over 12 min, a larger amount of carbon (27 nmol C) was needed to generate the DI spectrum for which 256 scans were coadded in approximately 7 min. The 9-fold higher concentration, coaddition of a larger number of scans for a single DI-FT-ICR MS spectrum (256 vs 17 for one segment) and corresponding reduction of chemical noise by approximately a factor of 4 contributed to an overall higher sensitivity (dynamic range: 260 with DI after SPE vs 95 with LC from original sample). However, the number of detected MFs was lower for the DI-FT-ICR MS (n = 3,907) as compared to the original sample measurement with LC-FT-ICR MS (n = 5,692; Figure 6) even without considering multiple detection of the same formula across segments. This confirms that the suppression of low abundance ions (often heteroatom-containing MFs) is reduced due to LC separation, possibly supported by the lower pH of the eluent. (28,44)

Figure 6

Figure 6. DOM chemodiversity in Arctic Ocean seawater. (a, b) Original sample AOhigh (circles, n = 5,692) measured at 88 μmol DOC L–1 with LC-FT-ICR MS and (c, d) the corresponding PPL-extracted sample AOhighSPE (triangles, n = 3,907) measured at 0.8 mmol DOC L–1 with DI-FT-ICR MS. Molecular H/C vs O/C (a, c) and H/C vs mass (b, d) for all detected MFs color coded by the signal-to-noise (S/N) ratio. The respective weighted-average values are indicated by markers on the axes. Circle size in (a, b) indicates the number of occurrences (1 ≤ n ≤ 9) of each molecular formula across all LC segments (14–24 min). Molecular H/C vs O/C (e) and H/C vs mass (f) for all detected MFs shared (gray, n = 2,806) or uniquely detected in original (AOhigh, red, n = 2,886), or the PPL extract measured with DI (AOhighSPE, yellow, n = 1101).

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The original sample measured with LC displayed a shift toward more oxygenated and less saturated as well as much larger DOM as compared to the DI measurement of its solid-phase extract (Figure 6, Figure SI 7, Table SI 5), as previously observed for SRFA. (28) In particular, MFs that were uniquely detected in the direct seawater analysis were more polar (i.e., with larger O/C ratio, Figure SI 6) and had a larger N/C and S/C ratio (Table SI 7), confirming the benefits of LC-FT-ICR MS for compounds highly relevant for investigation of the biological processes and carbon cycling. (2,45−47)
At an S/N ratio of 4, we identified 473 MFs in DI-FT-ICR MS measurement of AOhighSPE that were absent in both LC analyses of the original and extracted sample (Figures SI 30,34). Out of those, 387 MFs had an S/N < 15 in the DI spectrum and would likely not be detected if measured at the same concentration as the LC analyses. These MFs were characterized by low signal-to-noise, O/C, and H/C ratios in the DI spectrum (Figure SI 34) and hence represented compounds with lower polarity that were preferentially enriched by the PPL extraction.
The comparison between DI-FT-ICR MS of sample AOhighSPE and LC-FT-ICR MS of AOhigh indicated more degraded DOM (larger IDEG) with a lower contribution of terrestrially derived material (smaller ITerr, Table SI 6) in the nonextracted sample. This is notable, since at the same time, a larger relative contribution of terrestrial markers (t-Peaks) to the total intensity was found for the AOhigh sample as compared to AOhighSPE (Figures SI 13,14), highlighting uncertainties in the application of biogeochemical indices from DI-FT-ICR MS analyses.

Biogeochemical Implications

Original Water Analysis Revises View on Marine DOM Chemodiversity and Polarity

The current view on marine DOM as assessed with MS is largely based on SPE-extracts known for its consistent underestimation of e.g. the mean nominal oxidation state of carbon (NOSC) (48) and molecular weight as compared to bulk measurements. (49) Here we could demonstrate the bias of SPE in marine DOM on a molecular level leading to a predominant detection of less polar DOM, while neglecting a large fraction of polar, heteroatom-rich DOM. Likewise, our results indicate that a substantial fraction of terrestrial-derived DOM was previously overlooked in SPE samples of marine DOM. Such a comparison based on the same detection method was previously not possible, as all molecular-level analyses of marine DOM relied on desalting/extraction and native samples could not be measured.
Our direct analysis of original seawater samples provides a less biased view and allows for a better comparability between samples and with other approaches using original water samples (spectroscopic methods like UV/vis, fluorescence, or FT-infrared spectroscopy). We note that despite the use of nonextracted, original samples, biases from ionization modes and instruments on the observed molecular composition of DOM still exist. (23,50) For the same reason, the results obtained from our new method cannot be directly compared to DI spectra acquired from extracts. Nevertheless, the biogeochemically most dynamic fraction of DOM (e.g., algal exudates, bacterial exometabolites, terrestrial DOM) (5,51,52) can now be better studied due to the increased sensitivity from the polarity separation and reduced suppression of heteroatom-containing DOM.

New Perspectives for DOM Research

The small volume requirements of the new method support studies where only a small sample volume is available (e.g., in sediment pore water) and also allow higher spatial (e.g., in soils) or temporal sample resolution (e.g., in culture experiments). The sensitivity of the method is unprecedented since the lowest absolute amount of carbon injected was only 2 nmol C (20 μmol DOC L–1). Given about 5,700 molecular formulas and 16,200 detected molecular features in a marine DOM sample and an average number of carbon atoms of 19, the mean absolute detectable amount for a molecular feature was around two femtomole. The linear response of the peak magnitudes now allows DOM characterization beyond the compositional analyses that uses normalized peak magnitudes. Instead, we can now use the peak magnitude directly or, alternatively, DOC concentration as the normalization factor for semiquantitative evaluations of MF abundances. In combination with the isomeric separation based on polarity, this method now allows revisiting controversial concepts regarding the long-term stability of marine organic matter and the fate of terrestrial organic matter in the ocean. (53,54)
Compared to DI analyses, the use of LC leads to a significant increase in the amount of data (up to 20 Gigabyte per sample with full profile mode and retaining the free induction decay for about 20–25 min data recoding time). This requires revised concepts for automated data processing (55) and quality control as well as statistical analysis. These additional efforts are justified given the less biased analysis and greater information gain, especially on the chemistry of DOM. Further improvements in sensitivity may also allow nontargeted environmental metabolomics studies performed with original seawater. Ultimately, we expect that novel biomarkers can be developed, making use of the high analytical sensitivity obtained from LC-FT-ICR MS to study environmental processes.

Data Availability

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Processed and quality checked data for all samples and segments are available from the UFZ Data Investigation Portal: https://doi.org/10.48758/ufz.14331. Raw MS files can be shared upon request.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.3c07219.

  • Additional information regarding DOC determination, instrument quality control, and method assessment, samples (Tables SI 1,2, Figure SI 1), model compounds (Tables SI 3,4, Figure SI 16), molecular descriptors and biogeochemical indices (Tables SI 5–7), LC setup (Figure SI 2), data processing (Figure SI 3), LC chromatograms (Figures SI 4–6, 12–15), chemodiversity (Figures SI 7–11), matrix effects (Figures SI 17–21), detector response (Figures SI 22–24), repeatability (Figures SI 25,26), pH effect (Figures SI 27,28), comparison with SPE extracts (Figures SI 29–34) (PDF)

  • Script for DataAnalysis (Bruker Daltonics, version 6.0) for LC-MS segmentation and spectra averaging (TXT)

  • List of surfactants (XLSX)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Authors
    • Oliver J. Lechtenfeld - Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany;  ProVIS−Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany;  Orcidhttps://orcid.org/0000-0001-5313-6014;  Email: [email protected]
    • Boris P. Koch - Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany;  University of Applied Sciences, An der Karlstadt 8, 27568 Bremerhaven, Germany;  Orcidhttps://orcid.org/0000-0002-8453-731X;  Email: [email protected]
  • Authors
    • Jan Kaesler - Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany
    • Elaine K. Jennings - Department of Environmental Analytical Chemistry, Research Group BioGeoOmics, Helmholtz Centre for Environmental Research − UFZ, Permoserstraße 15, 04318 Leipzig, Germany;  Orcidhttps://orcid.org/0000-0003-4508-0190
  • Funding

    This work was supported by the Helmholtz Association within the Research Program POF-IV and the German Research Foundation (DFG), project number 428639365.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We thank Klaus-Holger Knorr and Svenja Agethen (WWU Münster) for providing the peat pore water. We are grateful for using the analytical facilities of ProVIS–Centre for Chemical Microscopy within the Helmholtz Centre for Environmental Research Leipzig, which is supported by the European Regional Development Funds (EFRE - Europe funds Saxony) and the Helmholtz Association. We would also like to thank the other lab members, especially Martin Lohse, Maria Paula da Silva, Limei Han, Rebecca Matos, Carsten Simon, Jan Tebben, and Xianyu Kong, for helpful discussions and insights. Funding for E.K.J. was provided by the German Research Foundation (DFG), project number 428639365. Finally, we thank the editor, Fernando Rosario-Ortiz, as well as four anonymous reviewers for their constructive comments that greatly improved the manuscript.

References

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    Dittmar, Thorsten; Koch, Boris; Hertkorn, Norbert; Kattner, Gerhard
    Limnology and Oceanography: Methods (2008), 6 (June), 230-235CODEN: LOMIBY; ISSN:1541-5856. (American Society of Limnology and Oceanography)
    A simple protocol is presented for the solid-phase extn. of dissolved org. matter (SPE-DOM) from seawater using com. prepacked cartridges. The method does not require major instrumentation and can be performed in the field. Modified styrene divinyl benzene polymer type sorbents (Varian PPL and ENV) and sorbents of a silica structure bonded with different hydrocarbon chains (Varian C8, C18, C18OH, and C18EWP) were considered. Except for C18OH, which heavily contaminated the samples, none of the sorbents leached significant amts. of dissolved org. carbon (DOC) or nitrogen (DON). Samples from the North Brazil shelf with strong mixing gradients of terrigenous and marine DOM were used to compare the various sorbents. PPL was the most efficient-on av., 62% of DOC was recovered as salt-free exts. C18 was found to be most efficient among the silica-based sorbents, but it showed only two-thirds of the extn. efficiency of PPL. As indicated by [1H]NMR, C/N, and δ13C analyses, PPL extd. a more representative proportion of DOM than C18. Therefore, PPL was used for comparative studies in the Gulf of Mexico and Antarctica. From brackish marsh and river waters, 65% and 62% of total DOC, resp., could be extd. For purely marine DOM in Antarctica and the deep sea, the extn. efficiency was lower (43% on av.). The efficiency of the new method to isolate marine DOM is better than or similar to highly laborious methods. A further advantage is the complete desalination of the sample. The isolation of a major DOM fraction, which is salt-free, offers many possibilities to further characterize DOM by advanced anal. techniques.
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  7. 7
    Jerusalén-Lleó, E.; Nieto-Cid, M.; Fuentes-Santos, I.; Dittmar, T.; Álvarez-Salgado, X. A. Solid phase extraction of ocean dissolved organic matter with PPL cartridges: efficiency and selectivity. Frontiers in Marine Science 2023, 10, 1159762,  DOI: 10.3389/fmars.2023.1159762
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  8. 8
    Kong, X.; Jendrossek, T.; Ludwichowski, K. U.; Marx, U.; Koch, B. P. Solid-Phase Extraction of Aquatic Organic Matter: Loading-Dependent Chemical Fractionation and Self-Assembly. Environ. Sci. Technol. 2021, 55 (22), 15495– 15504,  DOI: 10.1021/acs.est.1c04535
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    8
    Solid-Phase Extraction of Aquatic Organic Matter: Loading-Dependent Chemical Fractionation and Self-Assembly
    Kong, Xianyu; Jendrossek, Thomas; Ludwichowski, Kai-Uwe; Marx, Ute; Koch, Boris P.
    Environmental Science & Technology (2021), 55 (22), 15495-15504CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
    Dissolved org. matter (DOM) is an important component in marine and freshwater environments and plays a fundamental role in global biogeochem. cycles. In the past, optical and mol.-level anal. techniques evolved and improved our mechanistic understanding about DOM fluxes. For most mol. chem. techniques, sample desalting and enrichment is a prerequisite. Solid-phase extn. has been widely applied for concg. and desalting DOM. The major aim of this study was to constrain the influence of sorbent loading on the compn. of DOM exts. Here, we show that increased loading resulted in reduced extn. efficiencies of dissolved org. carbon (DOC), fluorescence and absorbance, and polar org. substances. Loading-dependent optical and chem. fractionation induced by the altered adsorption characteristics of the sorbent surface (styrene divinylbenzene polymer) and increased multilayer adsorption (DOM self-assembly) can fundamentally affect biogeochem. interpretations, such as the source of org. matter. Online fluorescence monitoring of the permeate flow allowed to empirically model the extn. process and to assess the degree of variability introduced by changing the sorbent loading in the extn. procedure. Our study emphasizes that it is crucial for sample comparison to keep the relative DOC loading (DOCload [wt %]) on the sorbent always similar to avoid chem. fractionation.
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  9. 9
    Raeke, J.; Lechtenfeld, O. J.; Wagner, M.; Herzsprung, P.; Reemtsma, T. Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra. Environ. Sci. Process Impacts 2016, 18 (7), 918– 27,  DOI: 10.1039/C6EM00200E
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    9
    Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra
    Raeke, Julia; Lechtenfeld, Oliver J.; Wagner, Martin; Herzsprung, Peter; Reemtsma, Thorsten
    Environmental Science: Processes & Impacts (2016), 18 (7), 918-927CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)
    Solid phase extn. (SPE) is often used for enrichment and clean-up prior to anal. of dissolved org. matter (DOM) by electrospray ionization (ESI) coupled to ultrahigh resoln. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It is generally accepted that extn. by SPE is not quant. with respect to carbon concn. However, little information is available on the selectivity of different SPE sorbents and the resulting effect for the acquired DOM mass spectra. Freshwater samples were extd. by the widely used PPL, HLB and C18 sorbents and the mol. compn. and size distribution of the DOM in the exts. and in the permeates was compared to the original sample. Dissolved org. carbon (DOC) recoveries ranged between 20% and 65% for the three tested SPE sorbents. Size-exclusion chromatog. coupled to org. carbon detection (SEC-OCD) revealed that limited recovery by PPL and HLB was primarily due to incomplete elution of a fraction of apparent high mol. wt. from the solid phase. In contrast, incomplete retention on the solid phase, mainly obsd. for the C18 cartridge, was attributed to a fraction of low mol. wt. The FT-ICR mass spectra of the original sample and the SPE exts. did not differ significantly in their mol. wt. distribution, but they showed sorbent specific differences in the degree of oxygenation and satn. We concluded that the selective enrichment of freshwater DOM by SPE is less crit. for subsequent FT-ICR MS anal., because those fractions that are not sufficiently recovered have comparatively small effects on the mass spectra. This was confirmed by the extn. of model compds., showing that very polar and small mols. are poorly extd., but also have a low response in ESI-MS. Of the three tested SPE cartridges the PPL material offered the best properties for DOM enrichment for subsequent FT-ICR MS anal. as it minimizes too strong and too weak DOM-sorbent interactions.
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  10. 10
    Li, Y.; Harir, M.; Lucio, M.; Kanawati, B.; Smirnov, K.; Flerus, R.; Koch, B. P.; Schmitt-Kopplin, P.; Hertkorn, N. Proposed Guidelines for Solid Phase Extraction of Suwannee River Dissolved Organic Matter. Anal. Chem. 2016, 88 (13), 6680– 8,  DOI: 10.1021/acs.analchem.5b04501
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    10
    Proposed Guidelines for Solid Phase Extraction of Suwannee River Dissolved Organic Matter
    Li, Yan; Harir, Mourad; Lucio, Marianna; Kanawati, Basem; Smirnov, Kirill; Flerus, Ruth; Koch, Boris P.; Schmitt-Kopplin, Philippe; Hertkorn, Norbert
    Analytical Chemistry (Washington, DC, United States) (2016), 88 (13), 6680-6688CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    This paper proposes improved guidelines for dissolved org. matter (DOM) isolation by solid phase extn. (SPE) with a styrene-divinylbenzene copolymer (PPL) sorbent, which has become an established method for the isolation of DOM from natural waters, because of its ease of application and appreciable carbon recovery. Suwannee River water was selected to systematically study the effects of crit. SPE variables such as loading mass, concn., flow rate, and up-scaling on the extn. selectivity of the PPL sorbent. High-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and proton NMR (1H NMR) spectroscopy were performed to interpret the DOM chem. space of eluates, as well as permeates and wash liqs. with mol. resoln. Up to 89% dissolved org. carbon (DOC) recovery was obtained with a DOC/PPL mass ratio of 1:800 at a DOC concn. of 20 mg/L. With the application of larger loading vols., low proportions of highly oxygenated compds. were retained on the PPL sorbent. The effects of the flow rate on the extn. selectivity of the sorbent were marginal. Up-scaling had a limited effect on the extn. selectivity with the exception of increased self-esterification with a methanol solvent, resulting in Me ester groups. Furthermore, the SPE/PPL ext. exhibited highly authentic characteristics in comparison with original water and reverse osmosis samples. These findings will be useful for reproducibly isolating DOM with representative mol. compns. from various sources and concns. and minimizing potential inconsistencies among interlab. comparative studies.
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  11. 11
    Lewis, C. B.; Walker, B. D.; Druffel, E. R. M. Isotopic and optical heterogeneity of solid phase extracted marine dissolved organic carbon. Marine Chemistry 2020, 219, 103752,  DOI: 10.1016/j.marchem.2020.103752
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    11
    Isotopic and optical heterogeneity of solid phase extracted marine dissolved organic carbon
    Lewis, Christian B.; Walker, Brett D.; Druffel, Ellen R. M.
    Marine Chemistry (2020), 219 (), 103752CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
    Marine dissolved org. carbon (DOC) is the ocean's largest exchangeable reservoir of org. carbon. The biogeochem. cycling of DOC plays an important role in ocean carbon storage on various timescales. Solid-phase extn. (SPE) is a process used to isolate DOC from seawater for biogeochem. anal. This study examines how DOC isotopic (Δ14C, δ13C) and optical (absorbance) properties of SPE-DOM change as a function of eluent vol. (and hydrophobicity). These properties were measured in 28 SPE-DOC fractions incrementally eluted from Bond Elut PPL (styrene-divinylbenzene polymer) cartridges, totaling 32 mL of methanol. We show that the early eluted SPE-DOC has distinctly different Δ14C and δ13C values than those eluted later. This study reveals isotopic heterogeneity as a function of SPE-DOC elution vol. These results show a partitioning of two distinct sources of SPE-DOC during elution, indicating a gradual transition from "marine-like" DOC to "terrestrial-like" DOC along a hydrophobicity continuum.
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  12. 12
    Johnson, W. M.; Kido Soule, M. C.; Kujawinski, E. B. Extraction efficiency and quantification of dissolved metabolites in targeted marine metabolomics. Limnol. Oceanogr.: Methods 2017, 15 (4), 417– 428,  DOI: 10.1002/lom3.10181
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  13. 13
    Zhou, Y.; He, D.; He, C.; Li, P.; Fan, D.; Wang, A.; Zhang, K.; Chen, B.; Zhao, C.; Wang, Y.; Shi, Q.; Sun, Y. Spatial changes in molecular composition of dissolved organic matter in the Yangtze River Estuary: Implications for the seaward transport of estuarine DOM. Sci. Total Environ. 2021, 759, 143531,  DOI: 10.1016/j.scitotenv.2020.143531
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    13
    Spatial changes in molecular composition of dissolved organic matter in the Yangtze River Estuary: Implications for the seaward transport of estuarine DOM
    Zhou, Yuping; He, Ding; He, Chen; Li, Penghui; Fan, Daidu; Wang, Anyue; Zhang, Kai; Chen, Baoshan; Zhao, Chen; Wang, Yuntao; Shi, Quan; Sun, Yongge
    Science of the Total Environment (2021), 759 (), 143531CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    The complexity of dissolved org. matter (DOM) limits our understanding of the estuarine carbon cycle. This study adopted a combination of bulk carbon isotope, optical techniques and ultra-high resoln. mass spectrometry to study the spatial heterogeneity and compositional variations of DOM across a latitudinal transect of the Yangtze River Estuary (YRE). Results show that the whole section of YRE received high abundance of protein-like C4 fluorescent component (0.66 ± 0.08 R.U.) and high relative abundance of aliph. compds. and peptides (8.28 ± 1.46%) from phytoplankton, which would contribute to the bioavailable DOM pool of the Eastern China Sea (ECS). However, multivariate anal. indicated that polycyclic aroms. and polyphenols from the Yangtze River experienced a significant decrease of 5% within the turbidity zone, creating a significant decrease of 0.08 in aromaticity index and modulating DOM content and compns. within the YRE. 1837 mol. formulas were identified to track dynamic behaviors of terrestrial DOM in the YRE. Mol. imprints showed the removal of terrestrial mols. in the turbidity zone indicated by the decrease of 753 in mol. quantity, when water masses mixing dild. the abundance of arom. compds. Adsorption and flocculation could serve important mechanisms to remove terrestrial DOM, promoting the burial of terrestrial DOM within estuarine sediments. Besides, some terrestrial mol. formulas were also detected in the ECS, suggesting the potential contribution of terrestrial DOM to the carbon stock of open seas after experiencing phys. and photochem. transformations. This research provides a comprehensive insight into spatial variations of estuarine DOM compn., underlining the important role of estuaries in sorting and transporting DOM.
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  14. 14
    Trufelli, H.; Palma, P.; Famiglini, G.; Cappiello, A. An Overview of Matrix Effects in Liquid Chromatography-Mass Spectrometry. Mass Spectrom. Rev. 2011, 30 (3), 491– 509,  DOI: 10.1002/mas.20298
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    14
    An overview of matrix effects in liquid chromatography-mass spectrometry
    Trufelli, Helga; Palma, Pierangela; Famiglini, Giorgio; Cappiello, Achille
    Mass Spectrometry Reviews (2011), 30 (3), 491-509CODEN: MSRVD3; ISSN:0277-7037. (John Wiley & Sons, Inc.)
    A review. Matrix-dependent signal suppression or enhancement represents a major drawback in quant. anal. with liq. chromatog. coupled to atm. pressure ionization mass spectrometry (LC-API-MS). Because matrix effects (ME) might exert a detrimental impact on important method parameters (limit of detection, limit of quantification, linearity, accuracy, and precision), they have to be tested and evaluated during validation procedure. This review gives a detailed description on when these phenomena might be expected, and how they can be evaluated. The major sources of ME are discussed and illustrated with examples from bioanal., pharmaceutical, environmental, and food anal. Because there is no universal soln. for ME, the main strategies to overcome these phenomena are described. Special emphasis is devoted to the sample-prepn. procedures as well as to the recent improvements on chromatog. and mass spectrometric conditions. An overview of the main calibration techniques to compensate for ME is also presented. All these solns. can be used alone or in combination to retrieve the performance of the LC-MS for a particular matrix-analyte combination. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:491-509, 2011.
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  15. 15
    Dulaquais, G.; Fourrier, P.; Maguer, J. F.; Denis, C.; Waeles, M.; Riso, R. Size exclusion chromatography and stable carbon isotopes reveal the limitations of solid phase extraction with PPL to capture autochthonous DOM production. Marine Chemistry 2023, 249, 104213,  DOI: 10.1016/j.marchem.2023.104213
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    15
    Size exclusion chromatography and stable carbon isotopes reveal the limitations of solid phase extraction with PPL to capture autochthonous DOM production
    Dulaquais, Gabriel; Fourrier, Pierre; Maguer, Jean Francois; Denis, Corentin; Waeles, Matthieu; Riso, Ricardo
    Marine Chemistry (2023), 249 (), 104213CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
    The study of the elemental and carbon isotopic compn. of dissolved org. matter (DOM) is of great interest in deciphering the origin and transformations of org. matter in estuarine and coastal environments. Styrene-divinylbenzene copolymer (PPL) sorbent is currently the most commonly used material for the isolation of DOM from environmental samples. It is notably used for the development of mol. formula-based indexes used to study DOM reactivity. However, any extn. procedure (including with PPL) will fractionate the DOM. If this fractionation is not well constrained it can lead to biased interpretations of the biogeochem. processes affecting DOM. In this work we investigate the fractionation effects of the PPL sorbent on the size class distribution of DOM and the carbon isotopic compn. of the PPL retentate. The use of size exclusion chromatog., that does not require a pre-concn. step, allows a precise study of the fractionation of DOM (including aromaticity) by the PPL resin. Extns. performed on two types of humic substances dissolved in artificial seawater, using the PPL resin, showed high extn. yield (> 85%) and the stable isotopic carbon compn. (δ13C) of these compds. was successfully recovered. These results indicate that salinity is not a parameter affecting extn. yield on PPL sorbent. For a hydrophilic compd. (atropine) the extn. efficiency was low (33%) and δ13C signature was underestimated. Size exclusion chromatog. measurements, in samples collected along a salinity gradient, demonstrate that the PPL sorbent strongly fractionates DOM. Although the DOM size class distributions in freshwaters and marine waters were initially different, their retentates were marked by similar size class distributions. This work demonstrates that PPL resin captures DOM compds. with less nitrogenous content and it seems to have a lower affinity for arom. compds. of marine origin than of terrigenous origin. The study of DOM distribution in a macro-tidal estuary demonstrated the limitations of PPL resin extn. in capturing an internal N-rich DOM prodn. event at the time of sampling. Futhermore, the isotopic compn. of the PPL resin retentate appears to depend on the extn. efficiency of the more hydrophobic compds. which changed along the salinity gradient. This study recommends careful interpretations of data that only rely on PPL extns., particularly for works tracking the origin of DOM in estuaries and comparing DOM compn. across ocean biogeochem. domains.
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  16. 16
    Spranger, T.; van Pinxteren, D.; Reemtsma, T.; Lechtenfeld, O. J.; Herrmann, H. 2D Liquid Chromatographic Fractionation with Ultra-high Resolution MS Analysis Resolves a Vast Molecular Diversity of Tropospheric Particle Organics. Environ. Sci. Technol. 2019, 53 (19), 11353– 11363,  DOI: 10.1021/acs.est.9b03839
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    16
    2D Liquid Chromatographic Fractionation with Ultra-high Resolution MS Analysis Resolves a Vast Molecular Diversity of Tropospheric Particle Organics
    Spranger, Tobias; Pinxteren, Dominik van; Reemtsma, Thorsten; Lechtenfeld, Oliver J.; Herrmann, Hartmut
    Environmental Science & Technology (2019), 53 (19), 11353-11363CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A two-dimensional liq. chromatog. fractionation method was combined with direct infusion electro-spray ionization Fourier transform-ion cyclotron resonance mass spectrometry to better resolve the high complexity of org. material in atm. particles. The no. of assigned mol. formulas increased by a factor of 2.3 for a fractionated sample (18,144) compared to a bulk sample anal. without fractionation (7819), while simultaneously allowing identification of 71,240 isomeric compds. Accounting for these isomers has an impact on the means and distributions of different descriptive sample parameters. More than 15,000 compds. were exclusively identified in the fractionated sample providing insights regarding organosulfate, reduced N-contg., and polyarom. compds. formation. A method to assign organonitrates and poly-organonitrates based on Kendrick mass defect anal. is presented. This work implicated anal. sepn. led to much more detailed insights into particulate orgs. compn.; more commonly applied direct infusion mass spectrometry studies can strongly underestimate compn. complexity and lead to biased assignments of bulk org. properties. Overall, the particulate orgs. compn. is far more complex than previously shown, while sepn. by better chromatog. techniques helped to understand atm. particle constituent formation processes.
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  17. 17
    Pemberton, J. A.; Lloyd, C. E. M.; Arthur, C. J.; Johnes, P. J.; Dickinson, M.; Charlton, A. J.; Evershed, R. P. Untargeted characterisation of dissolved organic matter contributions to rivers from anthropogenic point sources using direct-infusion and high-performance liquid chromatography/Orbitrap mass spectrometry. Rapid Commun. Mass Spectrom. 2020, 34, e8618,  DOI: 10.1002/rcm.8618
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    17
    Untargeted characterization of dissolved organic matter contributions to rivers from anthropogenic point sources using direct-infusion and high-performance liquid chromatography/Orbitrap mass spectrometry
    Pemberton, Jonathan A.; Lloyd, Charlotte E. M.; Arthur, Christopher J.; Johnes, Penny J.; Dickinson, Michael; Charlton, Adrian J.; Evershed, Richard P.
    Rapid Communications in Mass Spectrometry (2020), 34 (S4), e8618CODEN: RCMSEF; ISSN:0951-4198. (John Wiley & Sons Ltd.)
    Rationale : Anthropogenic org. inputs to freshwaters can exert detrimental effects on aquatic ecosystems, raising growing concern for both environmental conservation and water security. Current regulation by the EU water framework directive (European Union, 2000/60/EC) relates to org. pollution by monitoring selected micropollutants; however, aquatic ecosystem responses require a comprehensive understanding of dissolved org. matter (DOM) compn. The introduction of high-resoln. mass spectrometry (HRMS) is set to greatly increase our understanding of the compn. of DOM of both natural and anthropogenic origin derived from diffuse and point sources. Methods : DOM was extd. from riverine and treated sewage effluent using solid-phase extn. (SPE) and analyzed using dissolved org. carbon anal., direct-infusion high-resoln. mass spectrometry (DI-HRMS) and high-performance liq. chromatog. (HPLC)/HRMS. The data obtained were analyzed using univariate and multivariate statistics to demonstrate differences in background DOM, anthropogenic inputs and in-river mixing. Compd. identifications were achieved based on MS2 spectra searched against online databases. Results : DI-HRMS spectra showed the highly complex nature of all DOM SPE exts. Classification and visualization of exts. contg. many thousands of individual compds. were achieved using principal component anal. (PCA) and hierarchical cluster anal. Kruskal-Wallis analyses highlighted significant discriminating ions originating from the sewage treatment works for more in-depth investigation by HPLC/HRMS. The generation of MS2 spectra in HPLC/HRMS provided the basis for identification of anthropogenic compds. including; pharmaceuticals, illicit drugs, metabolites and oligomers, although many thousands of compds. remain unidentified. Conclusions : This new approach enables comprehensive anal. of DOM in exts. without any preconceived ideas of the compds. which may be present. This approach has the potential to be used as a high throughput, qual., screening method to det. if the compn. of point sources differs from that of the receiving water bodies, providing a new approach to the identification of hitherto unrecognised org. contribution to water bodies.
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  18. 18
    Liu, Z.; Sleighter, R. L.; Zhong, J.; Hatcher, P. G. The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry. Estuar. Coast. Shelf S. 2011, 92 (2), 205– 216,  DOI: 10.1016/j.ecss.2010.12.030
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    18
    The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry
    Liu, Zhanfei; Sleighter, Rachel L.; Zhong, Junyan; Hatcher, Patrick G.
    Estuarine, Coastal and Shelf Science (2011), 92 (2), 205-216CODEN: ECSSD3; ISSN:0272-7714. (Elsevier Ltd.)
    How dissolved org. matter (DOM) undergoes chem. changes during its transit from river to ocean remains a challenge due to its complex structure. DOM along a river transect from black waters to marine waters is characterized using an offline combination of reversed-phase HPLC (RP-HPLC) coupled to electrospray ionization Fourier transform ICR mass spectrometry (ESI-FTICR-MS), as well as tandem ESI-FTICR-MS. A H2O ext. from degraded wood that mainly consists of lignins is used for comparison to the DOM from this transect. The HPLC chromatograms of all DOM samples and the wood ext. show 2 major well-sepd. components; one is hydrophilic and the other is hydrophobic, based on their elution order from the C18 column. From the FTICR-MS anal. of the HPLC fractions, the hydrophilic components mainly contain low mol. wt. compds. (< 400 Da), while the hydrophobic fractions contain the vast majority of compds. of the bulk C18 extd. DOM. The wood ext. and the DOM samples from the transect of black waters to coastal marine waters show strikingly similar HPLC chromatograms, and the FTICR-MS anal. further indicates that a large fraction of mol. formulas from these samples are the same, existing as lignin-like compds. Tandem mass spectrometry expts. show that several representative mols. from the lignin-like compds. have similar functional group losses and fragmentation patterns, consistent with modified lignin structural entities in the wood ext. and these DOM samples. Taken together, these data suggest that lignin-derived compds. may survive the transit from the river to the coastal ocean and can accumulate there because of their refractory nature.
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  19. 19
    Hawkes, J. A.; Sjoberg, P. J. R.; Bergquist, J.; Tranvik, L. J. Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry. Faraday Discuss. 2019, 218, 52– 71,  DOI: 10.1039/C8FD00222C
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    19
    Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry
    Hawkes, J. A.; Sjoeberg, P. J. R.; Bergquist, J.; Tranvik, L. J.
    Faraday Discussions (2019), 218 (Challenges in Analysis of Complex Natural Mixtures), 52-71CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
    This paper investigates the relationship between apparent size distribution and mol. complexity of dissolved org. matter from the natural environment. We used a high pressure size exclusion chromatog. (HPSEC) method coupled to UV-Vis diode array detection (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) in order to compare the apparent size of natural org. matter, detd. by HPSEC-UV and the mol. mass detd. online by ESI-MS. We found that there was a clear discrepancy between the two methods, and found evidence for an important pool of org. matter that has a strong UV absorbance and no ESI-MS signal. Contrary to some previous research, we found no evidence that apparently high mol. wt. org. matter is constituted by aggregates of low mol. wt. (<1000 Da) material. Furthermore, our results suggest that the majority of apparent size variability within the ESI ionisable pool of org. matter is due to secondary interaction and exclusion effects on the HPSEC column, and not true differences in hydrodynamic size or intermol. aggregation.
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  20. 20
    Duarte, R. M. B. O.; Barros, A. C.; Duarte, A. C. Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography. Journal of Chromatography A 2012, 1249, 138– 146,  DOI: 10.1016/j.chroma.2012.06.022
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    20
    Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography
    Duarte, Regina M. B. O.; Barros, Ana C.; Duarte, Armando C.
    Journal of Chromatography A (2012), 1249 (), 138-146CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
    For the purpose of resolving the chem. heterogeneity of natural org. matter (NOM), comprehensive two-dimensional liq. chromatog. (LC × LC) was employed for the first time to map the hydrophobicity vs. mol. wt. (MW) distribution of two well-known complex org. mixts.: Suwannee River Fulvic Acids (SR-FA) and Pony Lake Fulvic Acids (PL-FA). Two methods have been developed using either a conventional reversed-phase (RP) silica column or a mixed-mode hydrophilic interaction column operating under aq. RP mode in the first dimension, and a size-exclusion column in the second dimension. The LC × LC fractions were screened online by UV at 254 nm, mol. fluorescence at excitation/emission wavelengths (λ Exc/λ Em) of 240/450 nm, and by evaporative light scattering. The MW distributions of these two NOM samples were further characterized by no. (Mn) and wt. (Mw) av. MW, and by polydispersity (Mw/Mn). Findings suggest that the combination of two independent sepn. mechanisms is promising in extend the range of NOM sepn. For the cases where NOM sepn. was accomplished, smaller Mw group fractions seem to be related to a more hydrophobic nature. Regardless of the detection method, the complete range of MW distribution provided by both comprehensive LC × LC methods was found to be lower than those reported in the literature.
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  21. 21
    Petras, D.; Koester, I.; Da Silva, R.; Stephens, B. M.; Haas, A. F.; Nelson, C. E.; Kelly, L. W.; Aluwihare, L. I.; Dorrestein, P. C. High-Resolution Liquid Chromatography Tandem Mass Spectrometry Enables Large Scale Molecular Characterization of Dissolved Organic Matter. Frontiers in Marine Science 2017, 4, 405,  DOI: 10.3389/fmars.2017.00405
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  22. 22
    Rowland, S. M.; Smith, D. F.; Blakney, G. T.; Corilo, Y. E.; Hendrickson, C. L.; Rodgers, R. P. Online Coupling of Liquid Chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry at 21 T Provides Fast and Unique Insight into Crude Oil Composition. Anal. Chem. 2021, 93 (41), 13749– 13754,  DOI: 10.1021/acs.analchem.1c01169
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    22
    Online Coupling of Liquid Chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry at 21 T Provides Fast and Unique Insight into Crude Oil Composition
    Rowland, Steven M.; Smith, Donald F.; Blakney, Gregory T.; Corilo, Yuri E.; Hendrickson, Christopher L.; Rodgers, Ryan P.
    Analytical Chemistry (Washington, DC, United States) (2021), 93 (41), 13749-13754CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    High magnetic field Fourier transform ICR (FT-ICR) mass spectrometry provides the highest mass resolving power and mass measurement accuracy for detailed characterization of complex chem. mixts. Here, the authors report the coupling of online liq. chromatog. of complex mixts. with a 21 T FT-ICR mass spectrometer. The high magnetic field enables large ion populations to be analyzed for each spectrum for a high dynamic range, with 3.2 million mass resolving power at m/z 400 (6.2 s transient duration) or 1.6 million (3.1 s transient duration) while maintaining high mass accuracy for mol. formula assignment (root-mean-square assignment error < 0.150 ppm). Thousands of unique elemental compns. are assigned per mass spectrum, which can be grouped by the heteroatom class, double bond equiv. (the no. of rings and double bonds to C), and C no. Figures of merit are discussed, as well as characterization of an Arabian heavy vacuum gas oil in terms of the ring no., compd. class, double bond equiv., and ion type. Consideration of elemental compn. and retention order provides addnl. structural information.
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  23. 23
    Patriarca, C.; Bergquist, J.; Sjoberg, P. J. R.; Tranvik, L.; Hawkes, J. A. Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples. Environ. Sci. Technol. 2018, 52 (4), 2091– 2099,  DOI: 10.1021/acs.est.7b04508
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    23
    Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples
    Patriarca, Claudia; Bergquist, Jonas; Sjoeberg, Per J. R.; Tranvik, Lars; Hawkes, Jeffrey A.
    Environmental Science & Technology (2018), 52 (4), 2091-2099CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Natural dissolved org. matter (DOM) is an ultracomplex mixt. that is essential to global carbon cycling but is poorly understood because of its complexity. The most powerful tool for the DOM characterization is high-resoln. mass spectrometry (HRMS) generally combined to direct infusion (DI) as sample introduction. Liq. chromatog. (LC) represents a compelling alternative to DI; however, state-of-the-art techniques involve only offline LC-HRMS approaches, which have important logistical drawbacks that make DOM anal. more challenging. This study introduces a new method based on online coupling of liq. chromatog. to high resoln. mass spectrometry, able to overcome the disadvantages of usual approaches. It is characterized by high reproducibility (% Bray-Curtis dissimilarity among replicates ≈ 2.5%), and it reduces transient complexity and contaminant interferences, thus increasing the signal-to-noise ratio (S/N), leading to the identification of an overall larger no. of formulas in the mixt. Moreover, the application of an in silico fractionation prior to the statistical anal. allows an easy, flexible, fast, and detailed comparison of DOM samples from a variety of sources with a single chromatog. run.
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  24. 24
    Sandron, S.; Rojas, A.; Wilson, R.; Davies, N. W.; Haddad, P. R.; Shellie, R. A.; Nesterenko, P. N.; Kelleher, B. P.; Paull, B. Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter. Environmental Science-Processes & Impacts 2015, 17 (9), 1531– 1567,  DOI: 10.1039/C5EM00223K
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    24
    Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter
    Sandron, Sara; Rojas, Alfonso; Wilson, Richard; Davies, Noel W.; Haddad, Paul R.; Shellie, Robert A.; Nesterenko, Pavel N.; Kelleher, Brian P.; Paull, Brett
    Environmental Science: Processes & Impacts (2015), 17 (9), 1531-1567CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)
    This review presents an overview of the sepn. techniques applied to the complex challenge of dissolved org. matter characterization. The review discusses methods for isolation of dissolved org. matter from natural waters, and the range of sepn. techniques used to further fractionate this complex material. The review covers both liq. and gas chromatog. techniques, in their various modes, and electrophoretic based approaches. For each, the challenges that the sepn. and fractionation of such an immensely complex sample poses is critically reviewed.
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  25. 25
    Jennings, E.; Kremser, A.; Han, L.; Reemtsma, T.; Lechtenfeld, O. J. Discovery of Polar Ozonation Byproducts via Direct Injection of Effluent Organic Matter with Online LC-FT-ICR-MS. Environ. Sci. Technol. 2022, 56 (3), 1894– 1904,  DOI: 10.1021/acs.est.1c04310
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    25
    Discovery of polar ozonation byproducts via direct injection of effluent organic matter with online LC-FT-ICR-MS
    Jennings, Elaine; Kremser, Arina; Han, Limei; Reemtsma, Thorsten; Lechtenfeld, Oliver J.
    Environmental Science & Technology (2022), 56 (3), 1894-1904CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
    Effluent org. matter (EfOM), a major ozone consumer during wastewater ozonation, is a complex mixt. of natural and anthropogenic org. mols. Ozonation of EfOM adds to mol. complexity by introducing polar and potentially mobile ozonation byproducts (OBPs). Currently, nontargeted direct infusion (DI) ultrahigh resoln. mass spectrometry (e.g. FT-ICR-MS) is used to study OBPs but requires sample extn., limiting the accessible polarity range of OBPs. To better understand the impact of ozonation on EfOM and the formation of polar OBPs, nonextd. effluent was analyzed by direct injection onto a reversed-phase liq. chromatog. system (RP-LC) online hyphenated with an FT-ICR-MS. Over four times more OBPs were detected in nonextd. EfOM compared to effluent extd. with solid phase extn. and measured with DI-FT-ICR-MS (13817 vs 3075). Over 1500 highly oxygenated OBPs were detected exclusively in early eluting fractions of nonextd. EfOM, indicating polar OBPs. Oxygenation of these newly discovered OBPs is higher than previously found, with an av. mol. DBE-O value of -3.3 and O/C ratio of 0.84 in the earliest eluting OBP fractions. These polar OBPs are consistently lost during extn. but may play an important role in understanding the environmental impact of ozonated EfOM. Moreover, 316 mol. formulas classified as nonreactive to ozone in DI-FT-ICR-MS can be identified with LC-FT-ICR-MS as isomers with varying degrees of reactivity, providing for the first time exptl. evidence of differential reactivity of complex org. matter isomers with ozone.
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    Flerus, R.; Koch, B. P.; Schmitt-Kopplin, P.; Witt, M.; Kattner, G. Molecular level investigation of reactions between dissolved organic matter and extraction solvents using FT-ICR MS. Marine Chemistry 2011, 124, 100– 107,  DOI: 10.1016/j.marchem.2010.12.006
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    26
    Molecular level investigation of reactions between dissolved organic matter and extraction solvents using FT-ICR MS
    Flerus, Ruth; Koch, Boris P.; Schmitt-Kopplin, Philippe; Witt, Matthias; Kattner, Gerhard
    Marine Chemistry (2011), 124 (1-4), 100-107CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
    The investigation of marine dissolved org. matter (DOM) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) requires the concn. and extn. of the DOM. Reactions between extn. solvent and DOM might influence data evaluation parameters, which are used to compare DOM of different origin. Potential reactions between methanol and solid-phase extd. marine DOM (SPE-DOM) and their influence on FT-ICR MS data were studied on a mol. level. For elemental formula assignments 9 isotopes were included in the evaluation, and different strategies based on isotope ratios and mass peak intervals were applied to achieve data sets of single assignments. DOM was eluted from the sorbent with methanol, methanol-13C-D4 and acetonitrile and stored at 20 °C and - 20 °C. Under both storage conditions H/D exchanges were detected. In addn., esterifications were detected in the ext. stored at 20 °C, but did not result in significant differences in the mass peak magnitudes. Hence, no changes of the weighted av. H/C and O/C ratios or other values such as Kendrick mass defect (KMD) and double bond equiv. (DBE) were obsd. Acetonitrile was tested as an alternative solvent. Both, methanol or acetonitrile can be used to ext. marine DOM from sorbents if samples are immediately stored at - 20 °C after the SPE process. However, FT-ICR MS data of DOM samples extd. with different solvents showed substantial differences as expected and should not be directly compared.
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  27. 27
    Longnecker, K. Dissolved organic matter in newly formed sea ice and surface seawater. Geochim. Cosmochim. Acta 2015, 171, 39– 49,  DOI: 10.1016/j.gca.2015.08.014
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    Dissolved organic matter in newly formed sea ice and surface seawater
    Longnecker, Krista
    Geochimica et Cosmochimica Acta (2015), 171 (), 39-49CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)
    Changes in sea ice in the Arctic will have ramifications on regional and global carbon cycling. Research to date has primarily focused on the regional impacts to biol. activity and global impacts on atm. processes. The current project considers the mol.-level compn. of org. carbon within sea ice compared to the org. matter in seawater. The project revealed that the compn. of org. matter within sea ice was more variable than the compn. of org. matter within the surface ocean. Furthermore, sea ice samples presented two distinct patterns in the compn. of org. matter with a portion of the sea ice samples contg. protein-like org. matter. Yet, the samples were collected in the early winter period when little biol. activity is expected. Thus, one hypothesis is that phys. processes acting during the formation of sea ice selectively transferred org. matter from seawater into sea ice. The present project expands our understanding of dissolved org. matter in sea ice and surface seawater and thereby increases our knowledge of carbon cycling in polar regions.
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  28. 28
    Han, L.; Kaesler, J.; Peng, C.; Reemtsma, T.; Lechtenfeld, O. J. Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions. Anal. Chem. 2021, 93 (3), 1740– 1748,  DOI: 10.1021/acs.analchem.0c04426
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    28
    Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions
    Han, Limei; Kaesler, Jan; Peng, Chang; Reemtsma, Thorsten; Lechtenfeld, Oliver J.
    Analytical Chemistry (Washington, DC, United States) (2021), 93 (3), 1740-1748CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Natural org. matter (NOM) is a highly complex mixt. of natural org. mols. The recent developments in NOM mol. characterization methods have shown that ESI-FT-ICR hyphenated with liq. chromatog. (LC) is a promising approach to also obtain chem. information (such as polarity and mol. size) about NOM mols. However, due to changing solvent compn. during gradient elution in LC-FT-ICR-MS, ionization conditions also change throughout the chromatog. sepn. process. In this study, we applied a post-LC column counter gradient (CG) to ensure stable solvent conditions for transient ESI-MS signals. Suwanee River Fulvic Acid (SRFA) std. and a peat pore water were used as representative dissolved NOM samples for method development and validation. Our results show that in polar NOM fractions (which elute with <50% methanol) the TIC intensity and no. of assigned mol. formulas were increased by 48% and 20%, as compared to the std. gradient (SG) method. Further application of a Q-isolation and selective ion accumulation for low abundance fractions revealed over 3 times more mol. formulas (esp. for CHNO, CHOS, CHNOS formula classes) than in full scan mode. The no. of detected highly polar NOM compds. (with elemental ratios H/C < 1, O/C > 0.6) were more than 20 times larger for CG-LC mode as compared to direct infusion (DI) (5715 vs 266 MF). We conclude that the application of a postcolumn counter gradient in LC-FT-ICR-MS analyses of NOM offers novel insight into the most polar fractions of NOM which are inaccessible in conventional DI measurements.
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  29. 29
    Lechtenfeld, O. J.; Koch, B. P.; Gašparović, B.; Frka, S.; Witt, M.; Kattner, G. The influence of salinity on the molecular and optical properties of surface microlayers in a karstic estuary. Marine Chemistry 2013, 150, 25– 38,  DOI: 10.1016/j.marchem.2013.01.006
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    29
    The influence of salinity on the molecular and optical properties of surface microlayers in a karstic estuary
    Lechtenfeld, Oliver J.; Koch, Boris P.; Gasparovic, Blazenka; Frka, Sanja; Witt, Matthias; Kattner, Gerhard
    Marine Chemistry (2013), 150 (), 25-38CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
    Sea-surface microlayers and the corresponding underlying waters of the karstic Krka Estuary (Croatia) were studied with respect to optical and mol. properties of dissolved org. matter (DOM). Solid-phase extd. DOM was sepd. by reversed-phase chromatog. and analyzed with ultra-high resoln. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The no. and summed magnitudes of FT-ICR MS peaks, enriched in the microlayer, increased with increasing salinity along the estuary. The mol. H to C ratio (as a measure of polarity) of enriched compds. was higher for the low salinity samples than for a high salinity marine station, which we propose is a consequence of a salt-mediated sepn. mechanism. Absorption and fluorescence of all samples decreased along the estuary with the microlayer samples showing higher absorption than the underlying water. Chromatog. and FT-ICR MS data revealed a distinct shift towards a smaller mol. size in the microlayer compared to the underlying water. The redistribution of dissolved org. carbon within chromatog. fractions and the decrease in mol. size was interpreted to result from photodegrdn. and/or microbial reprocessing. Collision induced dissocn. of selected FT-ICR MS mass peaks revealed the presence of S-contg. anthropogenic surfactants enriched in the microlayer. Mol. level study of estuarine surface microlayers will help to better understand the highly dynamic character of these systems, the accumulation of natural org. matter and anthropogenic pollutants and the role of surface microlayers for the sea-air energy exchange.
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  30. 30
    Kim, S.; Kramer, R. W.; Hatcher, P. G. Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the van Krevelen diagram. Anal. Chem. 2003, 75 (20), 5336– 44,  DOI: 10.1021/ac034415p
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    30
    Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the Van Krevelen diagram
    Kim, Sunghwan; Kramer, Robert W.; Hatcher, Patrick G.
    Analytical Chemistry (2003), 75 (20), 5336-5344CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool in the study of natural org. matter (NOM) at the mol. level.1 Ultrahigh-resoln. ESI-MS analyses of NOM often produce very complicated spectra; therefore, visual presentation and structural interpretations of the spectra are difficult. To meet this anal. challenge, we herein propose and demonstrate an approach using the van Krevelen diagram. With this approach, complicated mass spectra can be visualized in a way that allows for (1) possible reaction pathways to be identified and presented, and (2) qual. analyses on major classes of compds. that comprise ultrahigh-resoln. spectra. The qual. analyses are in a good agreement with results obtained from analyses by other anal. techniques. Addnl., the van Krevelen diagram can be expanded to a 3D plot by using peak intensities or relative intensities as the z-axis. The 3D van Krevelen diagram allows for an evaluation of the relative significance of structurally related compds. The 3D plot can also be a useful tool for compositional differentiation among samples.
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  31. 31
    Flerus, R.; Lechtenfeld, O. J.; Koch, B. P.; McCallister, S. L.; Schmitt-Kopplin, P.; Benner, R.; Kaiser, K.; Kattner, G. A molecular perspective on the ageing of marine dissolved organic matter. Biogeosciences 2012, 9 (6), 1935– 1955,  DOI: 10.5194/bg-9-1935-2012
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    31
    A molecular perspective on the ageing of marine dissolved organic matter
    Flerus, R.; Lechtenfeld, O. J.; Koch, B. P.; McCallister, S. L.; Schmitt-Kopplin, P.; Benner, R.; Kaiser, K.; Kattner, G.
    Biogeosciences (2012), 9 (6), 1935-1955CODEN: BIOGGR; ISSN:1726-4170. (Copernicus Publications)
    Dissolved org. matter (DOM) was extd. by solid-phase extn. (SPE) from 137 water samples from different climate zones and different depths along an eastern Atlantic Ocean transect. The exts. were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addn., the amt. of dissolved org. carbon was detd. for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were obsd. between the magnitudes of 43% of the FT-ICR mass peaks and the ext. Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the mol. compn. to higher av. masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks, a degrdn. index (IDEG) was developed to compare the degrdn. state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, IDEG, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. DOM weighted normalized mass peak magnitudes were used to compare aged and recent SPE-DOM on a semi-quant. mol. basis. The magnitude comparison showed a continuum of different degrdn. rates for the detected compds. A high proportion of the compds. should persist, possibly modified by partial degrdn., in the course of thermohaline circulation. Prokaryotic (bacterial) prodn., transformation and accumulation of this very stable DOM occur primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that prodn. and degrdn. are dynamic processes.
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  32. 32
    Medeiros, P. M.; Seidel, M.; Niggemann, J.; Spencer, R. G. M.; Hernes, P. J.; Yager, P. L.; Miller, W. L.; Dittmar, T.; Hansell, D. A. A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean. Global Biogeochem. Cycles 2016, 30 (5), 689– 699,  DOI: 10.1002/2015GB005320
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    A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean
    Medeiros, Patricia M.; Seidel, Michael; Niggemann, Jutta; Spencer, Robert G. M.; Hernes, Peter J.; Yager, Patricia L.; Miller, William L.; Dittmar, Thorsten; Hansell, Dennis A.
    Global Biogeochemical Cycles (2016), 30 (5), 689-699CODEN: GBCYEP; ISSN:1944-9224. (Wiley-Blackwell)
    Marine dissolved org. matter (DOM) contains one of the largest exchangeable org. carbon pools on Earth. Riverine input represents an important source of DOM to the oceans, yet much remains to be learned about the fate of the DOM linking terrestrial to oceanic carbon cycles through rivers at the global scale. Here we use ultrahigh-resoln. mass spectrometry to identify 184 mol. formulas that are indicators of riverine inputs (referred to as t-Peaks) and to track their distribution in the deep North Atlantic and North Pacific Oceans. The t-Peaks were found to be enriched in the Amazon River, to be highly correlated with known tracers of terrigenous input, and to be obsd. in all samples from four different rivers characterized by vastly different landscapes and vegetation coverage spanning equatorial (Amazon and Congo), subtropical (Altamaha), and Arctic (Kolyma) regions. Their distribution reveals that terrigenous org. matter is injected into the deep ocean by the global meridional overturning circulation, indicating that a fraction of the terrigenous DOM introduced by rivers contributes to the DOM pool obsd. in the deep ocean and to the storage of terrigenous org. carbon. This novel mol. approach can be used to further constrain the transfer of DOM from land to sea, esp. considering that Fourier transform ion cyclotron resonance mass spectrometer anal. is becoming increasingly frequent in studies characterizing the mol. compn. of DOM in lakes, rivers, and the ocean.
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    Koch, B. P.; Ludwichowski, K.-U.; Kattner, G.; Dittmar, T.; Witt, M. Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS. Mar. Chem. 2008, 111 (3–4), 233– 241,  DOI: 10.1016/j.marchem.2008.05.008
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    33
    Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS
    Koch, Boris P.; Ludwichowski, Kai-Uwe; Kattner, Gerhard; Dittmar, Thorsten; Witt, Matthias
    Marine Chemistry (2008), 111 (3-4), 233-241CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
    Marine dissolved org. matter (DOM) was sepd. by reversed-phase (RP) liq. chromatog. method and analyzed with fluorescence/absorption detection and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). The three key characteristics of the RP method are: (a) the C18-RP column chosen provides enhanced sepn. when the aq. phase is 100% buffer-free water, and it does not degrade over time; (b) the water eluent adjusted to pH 7 significantly improves the resoln. of water sol. compds.; (c) the initial flow maintained at low levels improves the sepn. of polar compds. In samples, contg. fresh DOM, specific peaks were detected, which were absent in old DOM samples. The combination with size exclusion chromatog. (SEC) also demonstrated the relation between polarity and mol. size of DOM. FT-ICR-MS was applied to evaluate the quality of sepn. on a mol. scale demonstrating that physico-chem. characteristics of DOM can be related to mol. formulas. Sample exts. were sepd. into 4 preparative fractions, and a large suite of the identified mol. formulas only occurred in specific fractions. This is an important basis for the application of further anal. techniques in order to perform a more target-oriented anal. aiming at the detn. of source and process biomarkers for DOM.
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    Kim, D.; Kim, S.; Son, S.; Jung, M. J.; Kim, S. Application of Online Liquid Chromatography 7 T FT-ICR Mass Spectrometer Equipped with Quadrupolar Detection for Analysis of Natural Organic Matter. Anal. Chem. 2019, 91 (12), 7690– 7697,  DOI: 10.1021/acs.analchem.9b00689
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    34
    Application of Online Liquid Chromatography 7 T FT-ICR Mass Spectrometer Equipped with Quadrupolar Detection for Analysis of Natural Organic Matter
    Kim, Donghwi; Kim, Sungjune; Son, Seungwoo; Jung, Maeng-Joon; Kim, Sunghwan
    Analytical Chemistry (Washington, DC, United States) (2019), 91 (12), 7690-7697CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with quadrupolar detection (QPD), was applied for online liq. chromatog. (LC) MS anal. of natural org. matter (NOM). Although FT-ICR MS has emerged as an important anal. technique to study NOM, there are few previous reports on online LC FT-ICR MS anal. of NOM due to the long acquisition time (2-8 s) required to obtain high-resoln. mass spectra. The QPD technique provides a crit. advantage over the conventional dipolar detection (DPD) technique for LC-MS anal. because a spectrum with the same resolving power can be obtained in approx. half the acquisition time. QPD FT-ICR MS provides resolving powers ((m/(Δm50%))) of ∼300000 and 170000 at m/z 400 with acquisition times per scan of 1.2 and 0.8 s, resp. The reduced acquisition time per scan allows increased no. of acquisitions in a given LC anal. time, resulting in improved signal to noise (S/N) ratio and dynamic range in comparison to conventional methods. For example, 40% and 100% increases in the no. of detected peaks were obtained with LC QPD FT-ICR MS, in comparison to conventional LC DPD FT-ICR MS and direct-injection FT-ICR MS. It is also possible to perform more quant. comparison and mol. level investigation of NOMs with 2 μg of a NOM sample. The data presented herein demonstrate a proof of principle that QPD combined with LC FT-ICR MS is a sensitive anal. technique that can provide comprehensive information about NOM.
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  35. 35
    Hawkes, J. A.; Patriarca, C.; Sjöberg, P. J. R.; Tranvik, L. J.; Bergquist, J. Extreme isomeric complexity of dissolved organic matter found across aquatic environments. Limnology and Oceanography Letters 2018, 3 (2), 21– 30,  DOI: 10.1002/lol2.10064
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    Extreme isomeric complexity of dissolved organic matter found across aquatic environments
    Hawkes, Jeffrey A.; Patriarca, Claudia; Sjoeberg, Per J. R.; Tranvik, Lars J.; Bergquist, Jonas
    Limnology & Oceanography Letters (2018), 3 (2), 21-30CODEN: LOLIBT; ISSN:2378-2242. (John Wiley & Sons Ltd.)
    The natural aquatic environment contains an enormous pool of dissolved reduced carbon, present as ultra-complex mixts. that are constituted by an unknown no. of compds. at vanishingly small concns. We attempted to sep. individual structural isomers from several samples using online reversed-phase chromatog. with selected ion monitoring/tandem mass spectrometry, but found that isomeric complexity still presented a boundary to investigation even after chromatog. simplification of the samples. However, it was possible to det. that the structural complexity differed among samples. Our results also suggest that extreme structural complexity was a ubiquitous feature of dissolved org. matter (DOM) in all aquatic systems, meaning that this diversity may play similar roles for recalcitrance and degrdn. of DOM in all tested environments.
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  36. 36
    Felgate, S. L.; Craig, A. J.; Moodie, L. W. K.; Hawkes, J. Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522). Anal. Chem. 2023, 95 (16), 6559– 6567,  DOI: 10.1021/acs.analchem.2c05304
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    36
    Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522)
    Felgate, Stacey L.; Craig, Alexander J.; Moodie, Lindon W. K.; Hawkes, Jeffrey
    Analytical Chemistry (Washington, DC, United States) (2023), 95 (16), 6559-6567CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Recent methodol. advances have greatly increased our ability to characterize aquatic dissolved org. matter (DOM) using high-resoln. instrumentation, including NMR (NMR) and mass spectrometry (HRMS). Reliable DOM ref. materials are required for further method development and data set alignment but do not currently exist for the marine environment. This presents a major limitation for marine biogeochem. and related fields, including natural product discovery. To fill this resource gap, we have prepd. a coastal marine DOM ref. material (TRM-0522) from 45 m deep seawater obtained ~ 1 km offshore of Sweden's west coast. Over 3000 mol. formulas were assigned by direct infusion HRMS, confirming sample diversity, and the distribution of formulas in van Krevelen space was typical for a marine sample, with the majority of formulas in the region H/C 1-1.5 and O/C 0.3-0.7. The extd. DOM pool was more nitrogen (N)- and sulfur (S)-rich than a typical terrestrial ref. material (SRFA). MZmine3 processing of ultrahigh-performance liq. chromatog. (UPLC)-HRMS/MS data revealed 494 resolvable features (233 in neg. mode; 261 in pos. mode) over a wide range of retention times and masses. NMR data indicated low contributions from arom. protons and, generally speaking, low lignin, humic, and fulvic substances assocd. with terrestrial samples. Instead, carboxylic-rich aliph. mols. were the most abundant components, followed by carbohydrates and aliph. functionalities. This is consistent with a very low specific UV absorbance SUVA254 value of 1.52 L mg C-1 m-1. When combined with comparisons with existing terrestrial ref. materials (Suwannee River fulvic acid and Pony Lake fulvic acid), these results suggest that TRM-0522 is a useful and otherwise unavailable ref. material for use in marine DOM biogeochem.
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  37. 37
    Lohse, M.; Blaser, S.; Vetterlein, D.; Schluter, S.; Oburger, E.; Reemtsma, T.; Lechtenfeld, O. J. Online Nano Solid Phase Extraction Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry Workflow to Analyze Small Scale Gradients of Soil Solution Organic Matter in the Rhizosphere. Anal. Chem. 2020, 92 (15), 10442– 10449,  DOI: 10.1021/acs.analchem.0c00946
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    37
    Online Nano Solid Phase Extraction Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry Workflow to Analyze Small Scale Gradients of Soil Solution Organic Matter in the Rhizosphere
    Lohse, M.; Blaser, S. R. G. A.; Vetterlein, D.; Schlueter, S.; Oburger, E.; Reemtsma, T.; Lechtenfeld, O. J.
    Analytical Chemistry (Washington, DC, United States) (2020), 92 (15), 10442-10449CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    A new method combining online nano solid phase extn. coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was developed to ext. and analyze org. matter (OM) from microliter vols. of salt contg. soil soln. samples. This approach allows the reproducible anal. of only minute amts. of org. carbon (down to 10 ng C) without the need of further sample prepn. The new method was applied to unravel developing small-scale patterns of dissolved org. matter (DOM) in soil solns. of a soil column expt. in which Zea mays plants were grown for 3 wk. Soil soln. was sampled by micro suction cups from the undisturbed soil-root system once a week. Growth of the root system and, hence, position of individual roots relative to the suction cups was followed by X-ray computed tomog. (X-ray CT). Our method makes it possible to resolve the chem. complexity of soil soln. OM (up to 4300 mol. formulas from 2.5μL sample). This allows to observe chem. gradients in the rhizosphere on a mol. level over time. The increasing influence of roots on soil soln. OM is visible from higher mol. masses, an increasing degree of oxygenation and a higher fraction of formulas contg. heteroatoms. The online nano solid phase extn.-FT-ICR-MS method provides novel insight into the processes affecting DOM in the rhizosphere, such as root exudation, microbial processes, and soil org. matter stabilization.
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  38. 38
    De Nicolo, A.; Cantu, M.; D’Avolio, A. Matrix effect management in liquid chromatography mass spectrometry: the internal standard normalized matrix effect. Bioanalysis 2017, 9 (14), 1093– 1105,  DOI: 10.4155/bio-2017-0059
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    Matrix effect management in liquid chromatography mass spectrometry: the internal standard normalized matrix effect
    De Nicolo, Amedeo; Cantu, Marco; D'Avolio, Antonio
    Bioanalysis (2017), 9 (14), 1093-1105CODEN: BIOAB4; ISSN:1757-6180. (Future Science Ltd.)
    LC-MS is becoming a std. for many applications, thanks to high sensitivity and selectivity; nevertheless, some issues are still present, particularly due to matrix effect (ME). Considering this, the use of optimal internal stds. (ISs, usually stable-isotope labeled) is important, but not always possible because of cost or availability. Therefore, a deep investigation of the inter-lot variability of the ME and of the correcting power of the chosen IS (isotope-labeled or not) is mandatory. While the adoption of isotopically labeled ISs considered as a 'gold std.' to mitigate ME impact on anal. results, there is not consensus about the std. technique to evaluate it during method validation. In this paper, currently available techniques to evaluate, reduce or counterbalance ME are presented and discussed. Finally, these techniques were summarized in a flowchart for a robust management of ME, particularly considering the concept of 'internal std. normalized ME'.
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    da Silva, M. P.; Koch, B. P.; von Tümpling, W.; Herzsprung, P.; Kamjunke, N.; Reemtsma, T.; Schmitt-Kopplin, P.; Lechtenfeld, O. J. A guideline for the application of correlation analyses based on ultra-high resolution mass spectra of natural organic matter: The impact of intensity normalization methods. Submitted for publication.
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    Sleighter, R. L.; Chen, H.; Wozniak, A. S.; Willoughby, A. S.; Caricasole, P.; Hatcher, P. G. Establishing a measure of reproducibility of ultrahigh-resolution mass spectra for complex mixtures of natural organic matter. Anal. Chem. 2012, 84 (21), 9184– 91,  DOI: 10.1021/ac3018026
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    Establishing a Measure of Reproducibility of Ultrahigh-Resolution Mass Spectra for Complex Mixtures of Natural Organic Matter
    Sleighter, Rachel L.; Chen, Hongmei; Wozniak, Andrew S.; Willoughby, Amanda S.; Caricasole, Paolo; Hatcher, Patrick G.
    Analytical Chemistry (Washington, DC, United States) (2012), 84 (21), 9184-9191CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    This study describes a method for evaluating the reproducibility of replicate mass spectra acquired for complex natural org. matter (NOM) samples analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, with regard to both peak detection and peak magnitude. Because studies of NOM characterization utilize not only the emergence and disappearance of peaks but also changes in relative peak magnitude, it is important to establish that the differences between samples are significantly larger than those between sample replicates. Here, a method is developed for correcting strict signal-to-noise thresholds, along with a new scheme for assessing the reproducibility of peak magnitudes. Furthermore, a systematic approach for discerning when the comparison of samples by the presence or absence of peaks is appropriate and when it is necessary to compare based on the relative magnitude of the peaks is presented. A variety of 10 different types of NOM samples are analyzed in duplicate or triplicate instrumental injections or exptl. extns. A framework for these procedures is provided, and acceptable reproducibility levels are recommended.
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    Moran, X. A. G.; Gasol, J. M.; Arin, L.; Estrada, M. A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production. Marine Ecology-Progress Series 1999, 187, 31– 41,  DOI: 10.3354/meps187031
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    A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production
    Moran, Xose A. G.; Gasol, Josep M.; Arin, Laura; Estrada, Marta
    Marine Ecology: Progress Series (1999), 187 (), 31-41CODEN: MESEDT; ISSN:0171-8630. (Inter-Research)
    The performance of 2 types of glass fiber filters (GF/F: 0.7 μm; GF/C: 1.2 μm) and 2 membrane filters (PC0.2: polycarbonate 0.2 μm; CE0.22: mixed cellulose esters 0.22 μm) was tested in estg. chlorophyll a and primary prodn. with the 14C technique. Expts. were carried out with water samples from the NW Mediterranean, the NE Atlantic, and the Antarctic Ocean. The first expt. compared measurements of particulate org. C (POC) prodn. whereas the other 3 also considered total (TOC) and dissolved (DOC) C fixation. No significant differences among filters were found regarding chlorophyll a retention but large discrepancies existed in the amt. of labeled org. C retained in all the expts. Both types of glass fiber filters, esp. GF/F, yielded higher values of apparent PO14C recovery than the membrane filters. The GF/F-derived POC prodn. rates were up to twice the PC0.2-derived rates and 63% higher than CE0.22-derived ones. The estd. rates of phytoplanktonic DOC prodn. were higher with the membrane filters in comparison to the GF/F ones. This discrepancy was attributed to a high DO14C adsorption to the glass fibers of GF filters. Due to uncertainties in the magnitude of this process in other samples, it is concluded that GF filters are not suitable when particulate primary prodn. must be measured without interference of released dissolved products, and that membrane filters should be used instead.
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    Halewood, E.; Opalk, K.; Custals, L.; Carey, M.; Hansell, D. A.; Carlson, C. A. Determination of dissolved organic carbon and total dissolved nitrogen in seawater using High Temperature Combustion Analysis. Frontiers in Marine Science 2022, 9, 1061646,  DOI: 10.3389/fmars.2022.1061646
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    Fonvielle, J. A.; Felgate, S. L.; Tanentzap, A. J.; Hawkes, J. A. Assessment of sample freezing as a preservation technique for analysing the molecular composition of dissolved organic matter in aquatic systems. RSC Adv. 2023, 13 (35), 24594– 24603,  DOI: 10.1039/D3RA01349A
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    Assessment of sample freezing as a preservation technique for analysing the molecular composition of dissolved organic matter in aquatic systems
    Fonvielle, Jeremy A.; Felgate, Stacey L.; Tanentzap, Andrew J.; Hawkes, Jeffrey A.
    RSC Advances (2023), 13 (35), 24594-24603CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    Dissolved org. matter (DOM) is widely studied in environmental and biogeochem. sciences, but is susceptible to chem. and biol. degrdn. during sample transport and storage. Samples taken in remote regions, aboard ships, or in large nos. need to be preserved for later anal. without changing DOM compn. Here we compare high-resoln. mass spectra of solid phase extractable DOM before and after freezing at -20°C. We found that freezing increases compositional dissimilarity in DOM by between 0 to 18.2% (median = 2.7% across 7 sites) when comparing replicates that were frozen vs. unfrozen, i.e., processed immediately after sampling, as compared with differences between unfrozen replicates. The effects of freezing primarily consisted of a poorer detection limit, but were smaller than other sample prepn. and anal. steps, such as solid phase extn. and variable ionisation efficiency. Freezing samples for either 21 or 95 days led to similar and only slight changes in DOM compn., albeit with more variation for the latter. Therefore, we conclude that sample freezing on these time scales should not impede scientific study of aquatic DOM and can be used where it makes logistical sense, such as for large spatial surveys or study of archived samples.
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    Reemtsma, T.; Alder, L.; Banasiak, U. A multimethod for the determination of 150 pesticide metabolites in surface water and groundwater using direct injection liquid chromatography-mass spectrometry. J. Chromatogr A 2013, 1271 (1), 95– 104,  DOI: 10.1016/j.chroma.2012.11.023
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    A multimethod for the determination of 150 pesticide metabolites in surface water and groundwater using direct injection liquid chromatography-mass spectrometry
    Reemtsma, Thorsten; Alder, Lutz; Banasiak, Ursula
    Journal of Chromatography A (2013), 1271 (1), 95-104CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
    Based on available information for 293 pesticides (herbicides, insecticides, fungicides, biocides, growth regulators), 210 pesticide metabolites were selected for inclusion in a multi-method for groundwater and surface water anal. With the final method, 150 pesticide metabolites can be analyzed in groundwater and surface water by direct injection liq. chromatog./electro-spray ionization/tandem mass spectrometry with multiple-reaction monitoring. For most metabolites this is the first published anal. method. For all metabolites, linear calibration in drinking water was possible, with a lower limits of calibration, 0.1 μg/L, achieved for 142 analytes and 0.01 μg/L for 113 analytes. Matrix effects in groundwater and surface water compared to those in drinking water were moderate (±20%) for 87% of analytes. For crit. sample/analyte combinations, std. addn. must be used for correct quantification. This method allows an extensive study of the occurrence of previously unknown or undetectable pesticide metabolites in groundwater and surface water.
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    Simon, C.; Roth, V.-N.; Dittmar, T.; Gleixner, G. Molecular Signals of Heterogeneous Terrestrial Environments Identified in Dissolved Organic Matter: A Comparative Analysis of Orbitrap and Ion Cyclotron Resonance Mass Spectrometers. Frontiers in Earth Science 2018, 6, 138,  DOI: 10.3389/feart.2018.00138
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    Longnecker, K.; Oswald, L.; Soule, M. C. K.; Cutter, G. A.; Kujawinski, E. B. Organic sulfur: A spatially variable and understudied component of marine organic matter. Limnology and Oceanography Letters 2020, 5 (4), 305– 312,  DOI: 10.1002/lol2.10149
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    Organic sulfur: A spatially variable and understudied component of marine organic matter
    Longnecker, Krista; Oswald, Lisa; Kido Soule, Melissa C.; Cutter, Gregory A.; Kujawinski, Elizabeth B.
    Limnology & Oceanography Letters (2020), 5 (4), 305-312CODEN: LOLIBT; ISSN:2378-2242. (John Wiley & Sons Ltd.)
    Sulfur (S) is a major heteroatom in org. matter. This project evaluated spatial variability in the concn. and mol.-level compn. of org. sulfur along gradients of depth and latitude. We measured the concn. of total org. sulfur (TOS) directly from whole seawater. Our data reveal high variability in org. sulfur, relative to established variability in total org. carbon or nitrogen. The deep ocean contained significant amts. of org. sulfur, and the concn. of TOS in North Atlantic Deep Water (NADW) decreased with increasing age while total org. carbon remained stable. Anal. of dissolved org. matter exts. by ultrahigh resoln. mass spectrometry revealed that 6% of elemental formulas contained sulfur. The sulfur-contg. compds. were structurally diverse, and showed higher nos. of sulfur-contg. elemental formulas as NADW moved southward. These measurements of org. sulfur in seawater provide the foundation needed to define the factors controlling org. sulfur in the global ocean.
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    Wagner, S.; Riedel, T.; Niggemann, J.; Vahatalo, A. V.; Dittmar, T.; Jaffe, R. Linking the Molecular Signature of Heteroatomic Dissolved Organic Matter to Watershed Characteristics in World Rivers. Environ. Sci. Technol. 2015, 49 (23), 13798– 13806,  DOI: 10.1021/acs.est.5b00525
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    Linking the Molecular Signature of Heteroatomic Dissolved Organic Matter to Watershed Characteristics in World Rivers
    Wagner, Sasha; Riedel, Thomas; Niggemann, Jutta; Vahatalo, Anssi V.; Dittmar, Thorsten; Jaffe, Rudolf
    Environmental Science & Technology (2015), 49 (23), 13798-13806CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Large world rivers are significant sources of dissolved org. matter (DOM) to the oceans. Watershed geomorphol. and land use can drive the quality and reactivity of DOM. Detg. the mol. compn. of riverine DOM is essential for understanding its source, mobility and fate across landscapes. Here, DOM from the main stem of 10 global rivers covering a wide climatic range and land use features was molecularly characterized via ultrahigh-resoln. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). FT-ICR mass spectral data revealed an overall similarity in mol. components among the rivers. However, when focusing specifically on the contribution of nonoxygen heteroat. mol. formulas (CHON, CHOS, CHOP, etc.) to the bulk mol. signature, patterns relating DOM compn. and watershed land use became apparent. Greater abundances of N- and S-contg. mol. formulas were identified as unique to rivers influenced by anthropogenic inputs, whereas rivers with primarily forested watersheds had DOM signatures relatively depleted in heteroat. content. A strong correlation between cropland cover and dissolved black N was established when focusing specifically on the pyrogenic class of compds. This study demonstrated how changes in land use directly affect downstream DOM quality and could impact C and nutrient cycling on a global scale.
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    LaRowe, D. E.; Van Cappellen, P. Degradation of natural organic matter: A thermodynamic analysis. Geochim. Cosmochim. Acta 2011, 75 (8), 2030– 2042,  DOI: 10.1016/j.gca.2011.01.020
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    Degradation of natural organic matter: A thermodynamic analysis
    LaRowe, Douglas E.; Van Cappellen, Philippe
    Geochimica et Cosmochimica Acta (2011), 75 (8), 2030-2042CODEN: GCACAK; ISSN:0016-7037. (Elsevier B.V.)
    The oxidative degrdn. of org. matter is a key process in the biogeochem. functioning of the earth system. Quant. models of org. matter degrdn. are therefore essential for understanding the chem. state and evolution of the Earth's near-surface environment, and to forecast the biogeochem. consequences of ongoing regional and global change. The complex nature of biol. produced org. matter represents a major obstacle to the development of such models, however. The authors compare the energetics of the oxidative degrdn. of a large no. of naturally occurring org. compds. By relating the Gibbs energies of half reactions describing the complete mineralization of the compds. to their av. nominal carbon oxidn. state, it becomes possible to est. the energetic potential of the compds. based on major element (C, H, N, O, P, S) ratios. The new energetic description of org. matter can be combined with bioenergetic theory to rationalize obsd. patterns in the decompn. of natural org. matter. For example, the persistence of cell membrane derived compds. and complex orgs. in anoxic settings is consistent with their limited catabolic potential under these environmental conditions. The proposed approach opens the way to include the thermodn. properties of org. compds. in kinetic models of org. matter degrdn.
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    Hawkes, J. A.; D’Andrilli, J.; Agar, J. N.; Barrow, M. P.; Berg, S. M.; Catalán, N.; Chen, H.; Chu, R. K.; Cole, R. B.; Dittmar, T.; Gavard, R.; Gleixner, G.; Hatcher, P. G.; He, C.; Hess, N. J.; Hutchins, R. H. S.; Ijaz, A.; Jones, H. E.; Kew, W.; Khaksari, M.; Palacio Lozano, D. C.; Lv, J.; Mazzoleni, L. R.; Noriega Ortega, B. E.; Osterholz, H.; Radoman, N.; Remucal, C. K.; Schmitt, N. D.; Schum, S. K.; Shi, Q.; Simon, C.; Singer, G.; Sleighter, R. L.; Stubbins, A.; Thomas, M. J.; Tolic, N.; Zhang, S.; Zito, P.; Podgorski, D. C. An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry: Are we getting the same answer?. Limnol. Oceanogr.: Methods 2020, 18 (6), 235– 258,  DOI: 10.1002/lom3.10364
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    An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry: Are we getting the same answer?
    Hawkes, Jeffrey A.; D'Andrilli, Juliana; Agar, Jeffrey N.; Barrow, Mark P.; Berg, Stephanie M.; Catalan, Nuria; Chen, Hongmei; Chu, Rosalie K.; Cole, Richard B.; Dittmar, Thorsten; Gavard, Remy; Gleixner, Gerd; Hatcher, Patrick G.; He, Chen; Hess, Nancy J.; Hutchins, Ryan H. S.; Ijaz, Amna; Jones, Hugh E.; Kew, William; Khaksari, Maryam; Palacio Lozano, Diana Catalina; Lv, Jitao; Mazzoleni, Lynn R.; Noriega-Ortega, Beatriz E.; Osterholz, Helena; Radoman, Nikola; Remucal, Christina K.; Schmitt, Nicholas D.; Schum, Simeon K.; Shi, Quan; Simon, Carsten; Singer, Gabriel; Sleighter, Rachel L.; Stubbins, Aron; Thomas, Mary J.; Tolic, Nikola; Zhang, Shuzhen; Zito, Phoebe; Podgorski, David C.
    Limnology and Oceanography: Methods (2020), 18 (6), 235-258CODEN: LOMIBY; ISSN:1541-5856. (John Wiley & Sons, Inc.)
    High-resoln. mass spectrometry (HRMS) has become a vital tool for dissolved org. matter (DOM) characterization. The upward trend in HRMS anal. of DOM presents challenges in data comparison and interpretation among labs. operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with ref. samples so that data can be robustly compared among research groups. To this end, four identically prepd. DOM samples were each measured by 16 labs., using 17 com. purchased instruments, using pos.-ion and neg.-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified ∼1000 common ions in both neg.- and pos.-ion modes over a wide range of m/z values and chem. space, as detd. by van Krevelen diagrams. Calcd. metrics of abundance-weighted av. indexes (H/C, O/C, aromaticity, and m/z) of the commonly detected ions showed that hydrogen satn. and aromaticity were consistent for each ref. sample across the instruments, while av. mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
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    Hertkorn, N.; Frommberger, M.; Witt, M.; Koch, B. P.; Schmitt-Kopplin, P.; Perdue, E. M. Natural organic matter and the event horizon of mass spectrometry. Anal. Chem. 2008, 80 (23), 8908– 19,  DOI: 10.1021/ac800464g
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    Natural Organic Matter and the Event Horizon of Mass Spectrometry
    Hertkorn, N.; Frommberger, M.; Witt, M.; Koch, B.; Schmitt-Kopplin, Ph.; Perdue, E. M.
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    UltraMassExplorer: a browser-based application for the evaluation of high-resolution mass spectrometric data
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    Rationale : High-resoln. mass spectrometry (HRMS) with high sample throughput has become an important anal. tool for the anal. of highly complex samples and data processing has become a major challenge for the user community. Evaluating direct-infusion HRMS data without automated tools for batch processing can be a time-consuming step in the anal. pipeline. Therefore, we developed a new browser-based software tool for processing HRMS data. Methods : The software, named UltraMassExplorer (UME), was written in the R programming language using the shiny library to build the graphical user interface. The performance of the integrated formula library search algorithm was tested using HRMS data derived from analyses of up to 50 exts. of marine dissolved org. matter. Results : The software supports the processing of lists of calibrated masses of neutral, protonated or deprotonated mols., with masses of up to 700 Da and a mass accuracy <3 ppm. In the performance test, the no. of assigned peaks per s increased with the no. of submitted peaks and reached a max. rate of 4745 assigned peaks per s. Conclusions : UME offers a complete data evaluation pipeline comprising a fast mol. formula assignment algorithm allowing for the swift reanal. of complete datasets, advanced filter functions and the export of data, meta-data and publication-quality graphics. Unique to UME is a fast and interactive connection between data and their visual representation. UME provides a new platform enabling an increased transparency, customization, documentation and comparability of datasets.
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  1. Stacey L. Felgate, Elizabeth Jakobsson, Andrea Balderrama Subieta, Lars J. Tranvik, Jeffrey A. Hawkes. Combined Quantification and Characterization of Dissolved Organic Matter by Liquid Chromatography–Mass Spectrometry Using Charged Aerosol Detection. Journal of the American Society for Mass Spectrometry 2024, 35 (12) , 2910-2917. https://doi.org/10.1021/jasms.4c00255
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  • Abstract

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    Figure 1

    Figure 1. Total assigned ion chromatograms (TAC, solid lines, right y-axis) and extracted ion chromatograms (EIC, dashed lines, left y-axis) for two Arctic Ocean samples (AOhigh (red) and AOlow (black)) and a pure water blank injection (BLK, gray). Two m/z values on the same nominal mass were selected, representing molecular formulas with higher O/C (m/z 353.0878: C16H18O9) and lower O/C ratios (m/z 353.1606: C18H26O7). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). 100% methanol was reached at 27 min (red marker). The color bars indicate the LC retention time segments, highlighted in subsequent figures. TAC represents 35% of the TIC in this example.

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    Figure 2

    Figure 2. LC-FT-ICR MS analysis of original seawater samples. (a) Summed intensity of assigned molecular formulas (MFs) based on formula classes (colors in legend) for the AOlow sample over all 11 LC segments (14–24 min). Colors on the retention time axis relate to labels displayed in (b). (b) Intensity-weighted average molecular H/C and O/C ratios for all segments of two seawater samples measured at native concentration (AOlow: 55 μmol DOC L–1, black and AOhigh: 88 μmol DOC L–1, red) with LC-FT-ICR MS. Note that the segment at 24 min (lighter colors) only contained very few MFs (AOlow: 100, AOhigh: 174). For details for sample AOlow, AOhigh and AOhighSPE, cf. Figures SI 8–11.

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    Figure 3

    Figure 3. Effect of salt on the peak intensities of original peat pore water (PPW) measured by LC-FT-ICR MS. (a) Distribution of relative differences between peak intensities (δRAW) of molecular formulas (MFs) detected without (PPWS0) and with salt (PPWS35; 35 g L–1 NaCl) injected at 80 μmol DOC L–1 for individual LC-segments (14–22 min, # MFs: 105 < n < 1937; with 25th, median, and 75th percentile as white lines). The dashed lines indicate the peak intensity repeatability limits (cf. Figure SI 25). (b) Intensity-weighted average molecular H/C and O/C ratios for all segments between 14 and 22 min for PPW at 80 μmol DOC L–1 without (hexagons) and with salt (squares). Transparent symbols indicate segments < 14 min and > 22 min.

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    Figure 4

    Figure 4. Linearity of detector response. (a) Summed intensity of assigned molecular formulas (MFs; total assigned intensity) in individual LC-segments (7–24 min, 18 segments) of different concentrations (20–160 μmol DOC L–1) of salt-free peat pore water (PPWS0). Without salt addition, DOM in early segments (<13 min) can be observed, which was otherwise masked by the coelution of the salt matrix (cf. Figure SI 23) and the respective time of valve switching (green marker). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). The gray box on the retention time axis indicates data displayed in (b). (b) Linear regression of peak intensities for MFs detected in segments of the PPWS0. MF with R2 values > 0.98 (corresponding to a significant linear regression at α = 0.01) are shown, representing 63% (21 min)–86% (16 min) of MFs that were detected at all concentrations (75 < n < 814; with 25th, median, and 75th percentile as white lines). Segments < 13 min and > 21 min were omitted due to the low number of detected MFs for the 20 μmol DOC L–1.

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    Figure 5

    Figure 5. Comparison between an original (AOhigh, red) and PPL-extracted sample (AOhighSPE, blue) measured at 88 μmol DOC L–1 with LC-FT-ICR MS. (a) Summed intensity of assigned molecular formulas (total assigned intensity) in each segment (7–24 min, 18 segments). No MFs were assigned to segments < 14 min in the original sample AOhigh due to the coelution of salt and the respective time of valve switching (green marker). The yellow marker and dashed line indicate the retention time at which the first methanol reaches the MS (13 min). (b) Relative peak intensity difference (δRAW) of all shared MFs in original AOhigh and PPL-extracted AOhighSPE seawater. Positive values indicate higher peak intensity in the original sample. The striped part of each bar for AOhighSPE in (a) and solid line in (b) indicate the mean loss in intensity according to the bulk carbon-based extraction efficiency (40%).

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    Figure 6

    Figure 6. DOM chemodiversity in Arctic Ocean seawater. (a, b) Original sample AOhigh (circles, n = 5,692) measured at 88 μmol DOC L–1 with LC-FT-ICR MS and (c, d) the corresponding PPL-extracted sample AOhighSPE (triangles, n = 3,907) measured at 0.8 mmol DOC L–1 with DI-FT-ICR MS. Molecular H/C vs O/C (a, c) and H/C vs mass (b, d) for all detected MFs color coded by the signal-to-noise (S/N) ratio. The respective weighted-average values are indicated by markers on the axes. Circle size in (a, b) indicates the number of occurrences (1 ≤ n ≤ 9) of each molecular formula across all LC segments (14–24 min). Molecular H/C vs O/C (e) and H/C vs mass (f) for all detected MFs shared (gray, n = 2,806) or uniquely detected in original (AOhigh, red, n = 2,886), or the PPL extract measured with DI (AOhighSPE, yellow, n = 1101).

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  • References

    This article references 55 other publications.

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      The chem. structure of refractory marine dissolved org. matter (DOM) is still largely unknown. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS) was used to resolve the complex mixts. of DOM and provide valuable information on elemental compns. on a mol. scale. The authors characterized and compared DOM from two sharply contrasting aquatic environments, algal-derived DOM from the Weddell Sea (Antarctica) and terrigenous DOM from pore water of a tropical mangrove area in northern Brazil. Several thousand mol. formulas in the mass range of 300-600 Da were identified and reproduced in element ratio plots. On the basis of mol. elemental compn. and double-bond equiv. (DBE) an av. compn. was calcd. for marine DOM. O/C ratios in the marine samples were lower (0.36 ± 0.01) than in the mangrove pore-water sample (0.42). A small proportion of chem. formulas with higher mol. mass in the marine samples were characterized by very low O/C and H/C ratios probably reflecting amphiphilic properties. The av. no. of unsaturations in the marine samples was surprisingly high (DBE = 9.9; mangrove pore water: DBE = 9.4) most likely due to a significant contribution of carbonyl carbon. There was no significant difference in elemental compn. between surface and deep-water DOM in the Weddell Sea. Although there were some mols. with unique marine elemental compn., there was a conspicuous degree of similarity between the terrigenous and algal-derived end members. Approx. one third of the mol. formulas were present in all marine as well as in the mangrove samples. Different forms of microbial degrdn. ultimately lead to similar structural features that are intrinsically refractory, independent of the source of the org. matter and the environmental conditions where degrdn. took place.
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      Lechtenfeld, O. J.; Kattner, G.; Flerus, R.; McCallister, S. L.; Schmitt-Kopplin, P.; Koch, B. P. Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean. Geochim. Cosmochim. Acta 2014, 126, 321– 337,  DOI: 10.1016/j.gca.2013.11.009
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      Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean
      Lechtenfeld, Oliver J.; Kattner, Gerhard; Flerus, Ruth; McCallister, S. Leigh; Schmitt-Kopplin, Philippe; Koch, Boris P.
      Geochimica et Cosmochimica Acta (2014), 126 (), 321-337CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)
      More than 90% of the global ocean dissolved org. carbon (DOC) is refractory, has an av. age of 4000-6000 years and a lifespan from months to millennia. The fraction of dissolved org. matter (DOM) that is resistant to degrdn. is a long-term buffer in the global carbon cycle but its chem. compn., structure, and biochem. formation and degrdn. mechanisms are still unresolved. We have compiled the most comprehensive mol. dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extd. marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Mol. trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from -229‰ to -495‰) were combined to model an integrated degrdn. rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degrdn. rates for 1557 mass peaks indicate that numerous DOM mols. cycle on timescales much longer than the turnover of the bulk DOC pool (estd. residence times of up to ∼100 ka) and the range of validity of radiocarbon dating. Changes in elemental compn. were detd. by assigning mol. formulas to the detected mass peaks. The combination of residence times with mol. information enabled modeling of the av. elemental compn. of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 mol. formulas represented the most stable compn. in the oceanic environment ("island of stability"). These most persistent compds. encompass only a narrow range of the mol. elemental ratios H/C (av. of 1.17 ± 0.13), and O/C (av. of 0.52 ± 0.10) and mol. masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concns. in the surface waters were low (46.3 ± 3.3 μM) while the org. radiocarbon was significantly more depleted than that of the East Atlantic, representing av. surface water DOM ages of 4920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the mol. degrdn. index IDEG obtained from FT-ICR MS data. Further, we identified 339 mol. formulas which probably contribute to an increased DOC concn. in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate.
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      Koch, B. P.; Kattner, G.; Witt, M.; Passow, U. Molecular insights into the microbial formation of marine dissolved organic matter: recalcitrant or labile?. Biogeosciences 2014, 11 (15), 4173– 4190,  DOI: 10.5194/bg-11-4173-2014
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      Molecular insights into the microbial formation of marine dissolved organic matter: recalcitrant or labile?
      Koch, B. P.; Kattner, G.; Witt, M.; Passow, U.
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      The degrdn. of marine dissolved org. matter (DOM) is an important control variable in the global carbon cycle. For our understanding of the kinetics of org. matter cycling in the ocean, it is crucial to achieve a mechanistic and mol. understanding of its transformation processes. A long-term microbial expt. was performed to follow the prodn. of non-labile DOM by marine bacteria. Two different glucose concns. and dissolved algal exudates were used as substrates. We monitored the bacterial abundance, concns. of dissolved and particulate org. carbon (DOC, POC), nutrients, amino acids and transparent exopolymer particles (TEP) for 2 years. The mol. characterization of extd. DOM was performed by ultrahigh resoln. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) after 70 days and after ∼2 years of incubation. Although glucose quickly degraded, a non-labile DOC background (5-9% of the initial DOC) was generated in the glucose incubations. Only 20% of the org. carbon from the algal exudate degraded within the 2 years of incubation. The degrdn. rates for the nonlabile DOC background in the different treatments varied between 1 and 11 μmol DOCL.1 yr-1. Transparent exopolymer particles, which are released by microorganisms, were produced during glucose degrdn. but decreased back to half of the max. concn. within less than 3 wk (degrdn. rate: 25 μg xanthan gum equiv. L-1 d-1) and were below detection in all treatments after 2 years. Addnl. glucose was added after 2 years to test whether labile substrate can promote the degrdn. of background DOC (co-metab.; priming effect). A priming effect was not obsd. but the glucose addn. led to a slight increase of background DOC. The mol. anal. demonstrated that DOM generated during glucose degrdn. differed appreciably from DOM transformed during the degrdn. of the algal exudates. Our results led to several conclusions: (i) based on our exptl. setup, higher substrate concn. resulted in a higher concn. of nonlabile DOC; (ii) TEP, generated by bacteria, degrade rapidly, thus limiting their potential contribution to carbon sequestration; (iii) the mol. signatures of DOM derived from algal exudates and glucose after 70 days of incubation differed strongly from refractory DOM. After 2 years, however, the mol. patterns of DOM in glucose incubations were more similar to deep ocean DOM whereas the degraded exudate was still different.
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      Dittmar, T.; Koch, B.; Hertkorn, N.; Kattner, G. A simple and efficient method for the solid-phase extraction of dissolved organic matter (SPE-DOM) from seawater. Limnology and Oceanography-Methods 2008, 6, 230– 235,  DOI: 10.4319/lom.2008.6.230
      6
      A simple and efficient method for the solid-phase extraction of dissolved organic matter (SPE-DOM) from seawater
      Dittmar, Thorsten; Koch, Boris; Hertkorn, Norbert; Kattner, Gerhard
      Limnology and Oceanography: Methods (2008), 6 (June), 230-235CODEN: LOMIBY; ISSN:1541-5856. (American Society of Limnology and Oceanography)
      A simple protocol is presented for the solid-phase extn. of dissolved org. matter (SPE-DOM) from seawater using com. prepacked cartridges. The method does not require major instrumentation and can be performed in the field. Modified styrene divinyl benzene polymer type sorbents (Varian PPL and ENV) and sorbents of a silica structure bonded with different hydrocarbon chains (Varian C8, C18, C18OH, and C18EWP) were considered. Except for C18OH, which heavily contaminated the samples, none of the sorbents leached significant amts. of dissolved org. carbon (DOC) or nitrogen (DON). Samples from the North Brazil shelf with strong mixing gradients of terrigenous and marine DOM were used to compare the various sorbents. PPL was the most efficient-on av., 62% of DOC was recovered as salt-free exts. C18 was found to be most efficient among the silica-based sorbents, but it showed only two-thirds of the extn. efficiency of PPL. As indicated by [1H]NMR, C/N, and δ13C analyses, PPL extd. a more representative proportion of DOM than C18. Therefore, PPL was used for comparative studies in the Gulf of Mexico and Antarctica. From brackish marsh and river waters, 65% and 62% of total DOC, resp., could be extd. For purely marine DOM in Antarctica and the deep sea, the extn. efficiency was lower (43% on av.). The efficiency of the new method to isolate marine DOM is better than or similar to highly laborious methods. A further advantage is the complete desalination of the sample. The isolation of a major DOM fraction, which is salt-free, offers many possibilities to further characterize DOM by advanced anal. techniques.
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    7. 7
      Jerusalén-Lleó, E.; Nieto-Cid, M.; Fuentes-Santos, I.; Dittmar, T.; Álvarez-Salgado, X. A. Solid phase extraction of ocean dissolved organic matter with PPL cartridges: efficiency and selectivity. Frontiers in Marine Science 2023, 10, 1159762,  DOI: 10.3389/fmars.2023.1159762
      There is no corresponding record for this reference.
    8. 8
      Kong, X.; Jendrossek, T.; Ludwichowski, K. U.; Marx, U.; Koch, B. P. Solid-Phase Extraction of Aquatic Organic Matter: Loading-Dependent Chemical Fractionation and Self-Assembly. Environ. Sci. Technol. 2021, 55 (22), 15495– 15504,  DOI: 10.1021/acs.est.1c04535
      8
      Solid-Phase Extraction of Aquatic Organic Matter: Loading-Dependent Chemical Fractionation and Self-Assembly
      Kong, Xianyu; Jendrossek, Thomas; Ludwichowski, Kai-Uwe; Marx, Ute; Koch, Boris P.
      Environmental Science & Technology (2021), 55 (22), 15495-15504CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      Dissolved org. matter (DOM) is an important component in marine and freshwater environments and plays a fundamental role in global biogeochem. cycles. In the past, optical and mol.-level anal. techniques evolved and improved our mechanistic understanding about DOM fluxes. For most mol. chem. techniques, sample desalting and enrichment is a prerequisite. Solid-phase extn. has been widely applied for concg. and desalting DOM. The major aim of this study was to constrain the influence of sorbent loading on the compn. of DOM exts. Here, we show that increased loading resulted in reduced extn. efficiencies of dissolved org. carbon (DOC), fluorescence and absorbance, and polar org. substances. Loading-dependent optical and chem. fractionation induced by the altered adsorption characteristics of the sorbent surface (styrene divinylbenzene polymer) and increased multilayer adsorption (DOM self-assembly) can fundamentally affect biogeochem. interpretations, such as the source of org. matter. Online fluorescence monitoring of the permeate flow allowed to empirically model the extn. process and to assess the degree of variability introduced by changing the sorbent loading in the extn. procedure. Our study emphasizes that it is crucial for sample comparison to keep the relative DOC loading (DOCload [wt %]) on the sorbent always similar to avoid chem. fractionation.
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    9. 9
      Raeke, J.; Lechtenfeld, O. J.; Wagner, M.; Herzsprung, P.; Reemtsma, T. Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra. Environ. Sci. Process Impacts 2016, 18 (7), 918– 27,  DOI: 10.1039/C6EM00200E
      9
      Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra
      Raeke, Julia; Lechtenfeld, Oliver J.; Wagner, Martin; Herzsprung, Peter; Reemtsma, Thorsten
      Environmental Science: Processes & Impacts (2016), 18 (7), 918-927CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)
      Solid phase extn. (SPE) is often used for enrichment and clean-up prior to anal. of dissolved org. matter (DOM) by electrospray ionization (ESI) coupled to ultrahigh resoln. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It is generally accepted that extn. by SPE is not quant. with respect to carbon concn. However, little information is available on the selectivity of different SPE sorbents and the resulting effect for the acquired DOM mass spectra. Freshwater samples were extd. by the widely used PPL, HLB and C18 sorbents and the mol. compn. and size distribution of the DOM in the exts. and in the permeates was compared to the original sample. Dissolved org. carbon (DOC) recoveries ranged between 20% and 65% for the three tested SPE sorbents. Size-exclusion chromatog. coupled to org. carbon detection (SEC-OCD) revealed that limited recovery by PPL and HLB was primarily due to incomplete elution of a fraction of apparent high mol. wt. from the solid phase. In contrast, incomplete retention on the solid phase, mainly obsd. for the C18 cartridge, was attributed to a fraction of low mol. wt. The FT-ICR mass spectra of the original sample and the SPE exts. did not differ significantly in their mol. wt. distribution, but they showed sorbent specific differences in the degree of oxygenation and satn. We concluded that the selective enrichment of freshwater DOM by SPE is less crit. for subsequent FT-ICR MS anal., because those fractions that are not sufficiently recovered have comparatively small effects on the mass spectra. This was confirmed by the extn. of model compds., showing that very polar and small mols. are poorly extd., but also have a low response in ESI-MS. Of the three tested SPE cartridges the PPL material offered the best properties for DOM enrichment for subsequent FT-ICR MS anal. as it minimizes too strong and too weak DOM-sorbent interactions.
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    10. 10
      Li, Y.; Harir, M.; Lucio, M.; Kanawati, B.; Smirnov, K.; Flerus, R.; Koch, B. P.; Schmitt-Kopplin, P.; Hertkorn, N. Proposed Guidelines for Solid Phase Extraction of Suwannee River Dissolved Organic Matter. Anal. Chem. 2016, 88 (13), 6680– 8,  DOI: 10.1021/acs.analchem.5b04501
      10
      Proposed Guidelines for Solid Phase Extraction of Suwannee River Dissolved Organic Matter
      Li, Yan; Harir, Mourad; Lucio, Marianna; Kanawati, Basem; Smirnov, Kirill; Flerus, Ruth; Koch, Boris P.; Schmitt-Kopplin, Philippe; Hertkorn, Norbert
      Analytical Chemistry (Washington, DC, United States) (2016), 88 (13), 6680-6688CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      This paper proposes improved guidelines for dissolved org. matter (DOM) isolation by solid phase extn. (SPE) with a styrene-divinylbenzene copolymer (PPL) sorbent, which has become an established method for the isolation of DOM from natural waters, because of its ease of application and appreciable carbon recovery. Suwannee River water was selected to systematically study the effects of crit. SPE variables such as loading mass, concn., flow rate, and up-scaling on the extn. selectivity of the PPL sorbent. High-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and proton NMR (1H NMR) spectroscopy were performed to interpret the DOM chem. space of eluates, as well as permeates and wash liqs. with mol. resoln. Up to 89% dissolved org. carbon (DOC) recovery was obtained with a DOC/PPL mass ratio of 1:800 at a DOC concn. of 20 mg/L. With the application of larger loading vols., low proportions of highly oxygenated compds. were retained on the PPL sorbent. The effects of the flow rate on the extn. selectivity of the sorbent were marginal. Up-scaling had a limited effect on the extn. selectivity with the exception of increased self-esterification with a methanol solvent, resulting in Me ester groups. Furthermore, the SPE/PPL ext. exhibited highly authentic characteristics in comparison with original water and reverse osmosis samples. These findings will be useful for reproducibly isolating DOM with representative mol. compns. from various sources and concns. and minimizing potential inconsistencies among interlab. comparative studies.
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    11. 11
      Lewis, C. B.; Walker, B. D.; Druffel, E. R. M. Isotopic and optical heterogeneity of solid phase extracted marine dissolved organic carbon. Marine Chemistry 2020, 219, 103752,  DOI: 10.1016/j.marchem.2020.103752
      11
      Isotopic and optical heterogeneity of solid phase extracted marine dissolved organic carbon
      Lewis, Christian B.; Walker, Brett D.; Druffel, Ellen R. M.
      Marine Chemistry (2020), 219 (), 103752CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
      Marine dissolved org. carbon (DOC) is the ocean's largest exchangeable reservoir of org. carbon. The biogeochem. cycling of DOC plays an important role in ocean carbon storage on various timescales. Solid-phase extn. (SPE) is a process used to isolate DOC from seawater for biogeochem. anal. This study examines how DOC isotopic (Δ14C, δ13C) and optical (absorbance) properties of SPE-DOM change as a function of eluent vol. (and hydrophobicity). These properties were measured in 28 SPE-DOC fractions incrementally eluted from Bond Elut PPL (styrene-divinylbenzene polymer) cartridges, totaling 32 mL of methanol. We show that the early eluted SPE-DOC has distinctly different Δ14C and δ13C values than those eluted later. This study reveals isotopic heterogeneity as a function of SPE-DOC elution vol. These results show a partitioning of two distinct sources of SPE-DOC during elution, indicating a gradual transition from "marine-like" DOC to "terrestrial-like" DOC along a hydrophobicity continuum.
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    12. 12
      Johnson, W. M.; Kido Soule, M. C.; Kujawinski, E. B. Extraction efficiency and quantification of dissolved metabolites in targeted marine metabolomics. Limnol. Oceanogr.: Methods 2017, 15 (4), 417– 428,  DOI: 10.1002/lom3.10181
      There is no corresponding record for this reference.
    13. 13
      Zhou, Y.; He, D.; He, C.; Li, P.; Fan, D.; Wang, A.; Zhang, K.; Chen, B.; Zhao, C.; Wang, Y.; Shi, Q.; Sun, Y. Spatial changes in molecular composition of dissolved organic matter in the Yangtze River Estuary: Implications for the seaward transport of estuarine DOM. Sci. Total Environ. 2021, 759, 143531,  DOI: 10.1016/j.scitotenv.2020.143531
      13
      Spatial changes in molecular composition of dissolved organic matter in the Yangtze River Estuary: Implications for the seaward transport of estuarine DOM
      Zhou, Yuping; He, Ding; He, Chen; Li, Penghui; Fan, Daidu; Wang, Anyue; Zhang, Kai; Chen, Baoshan; Zhao, Chen; Wang, Yuntao; Shi, Quan; Sun, Yongge
      Science of the Total Environment (2021), 759 (), 143531CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      The complexity of dissolved org. matter (DOM) limits our understanding of the estuarine carbon cycle. This study adopted a combination of bulk carbon isotope, optical techniques and ultra-high resoln. mass spectrometry to study the spatial heterogeneity and compositional variations of DOM across a latitudinal transect of the Yangtze River Estuary (YRE). Results show that the whole section of YRE received high abundance of protein-like C4 fluorescent component (0.66 ± 0.08 R.U.) and high relative abundance of aliph. compds. and peptides (8.28 ± 1.46%) from phytoplankton, which would contribute to the bioavailable DOM pool of the Eastern China Sea (ECS). However, multivariate anal. indicated that polycyclic aroms. and polyphenols from the Yangtze River experienced a significant decrease of 5% within the turbidity zone, creating a significant decrease of 0.08 in aromaticity index and modulating DOM content and compns. within the YRE. 1837 mol. formulas were identified to track dynamic behaviors of terrestrial DOM in the YRE. Mol. imprints showed the removal of terrestrial mols. in the turbidity zone indicated by the decrease of 753 in mol. quantity, when water masses mixing dild. the abundance of arom. compds. Adsorption and flocculation could serve important mechanisms to remove terrestrial DOM, promoting the burial of terrestrial DOM within estuarine sediments. Besides, some terrestrial mol. formulas were also detected in the ECS, suggesting the potential contribution of terrestrial DOM to the carbon stock of open seas after experiencing phys. and photochem. transformations. This research provides a comprehensive insight into spatial variations of estuarine DOM compn., underlining the important role of estuaries in sorting and transporting DOM.
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    14. 14
      Trufelli, H.; Palma, P.; Famiglini, G.; Cappiello, A. An Overview of Matrix Effects in Liquid Chromatography-Mass Spectrometry. Mass Spectrom. Rev. 2011, 30 (3), 491– 509,  DOI: 10.1002/mas.20298
      14
      An overview of matrix effects in liquid chromatography-mass spectrometry
      Trufelli, Helga; Palma, Pierangela; Famiglini, Giorgio; Cappiello, Achille
      Mass Spectrometry Reviews (2011), 30 (3), 491-509CODEN: MSRVD3; ISSN:0277-7037. (John Wiley & Sons, Inc.)
      A review. Matrix-dependent signal suppression or enhancement represents a major drawback in quant. anal. with liq. chromatog. coupled to atm. pressure ionization mass spectrometry (LC-API-MS). Because matrix effects (ME) might exert a detrimental impact on important method parameters (limit of detection, limit of quantification, linearity, accuracy, and precision), they have to be tested and evaluated during validation procedure. This review gives a detailed description on when these phenomena might be expected, and how they can be evaluated. The major sources of ME are discussed and illustrated with examples from bioanal., pharmaceutical, environmental, and food anal. Because there is no universal soln. for ME, the main strategies to overcome these phenomena are described. Special emphasis is devoted to the sample-prepn. procedures as well as to the recent improvements on chromatog. and mass spectrometric conditions. An overview of the main calibration techniques to compensate for ME is also presented. All these solns. can be used alone or in combination to retrieve the performance of the LC-MS for a particular matrix-analyte combination. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:491-509, 2011.
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    15. 15
      Dulaquais, G.; Fourrier, P.; Maguer, J. F.; Denis, C.; Waeles, M.; Riso, R. Size exclusion chromatography and stable carbon isotopes reveal the limitations of solid phase extraction with PPL to capture autochthonous DOM production. Marine Chemistry 2023, 249, 104213,  DOI: 10.1016/j.marchem.2023.104213
      15
      Size exclusion chromatography and stable carbon isotopes reveal the limitations of solid phase extraction with PPL to capture autochthonous DOM production
      Dulaquais, Gabriel; Fourrier, Pierre; Maguer, Jean Francois; Denis, Corentin; Waeles, Matthieu; Riso, Ricardo
      Marine Chemistry (2023), 249 (), 104213CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
      The study of the elemental and carbon isotopic compn. of dissolved org. matter (DOM) is of great interest in deciphering the origin and transformations of org. matter in estuarine and coastal environments. Styrene-divinylbenzene copolymer (PPL) sorbent is currently the most commonly used material for the isolation of DOM from environmental samples. It is notably used for the development of mol. formula-based indexes used to study DOM reactivity. However, any extn. procedure (including with PPL) will fractionate the DOM. If this fractionation is not well constrained it can lead to biased interpretations of the biogeochem. processes affecting DOM. In this work we investigate the fractionation effects of the PPL sorbent on the size class distribution of DOM and the carbon isotopic compn. of the PPL retentate. The use of size exclusion chromatog., that does not require a pre-concn. step, allows a precise study of the fractionation of DOM (including aromaticity) by the PPL resin. Extns. performed on two types of humic substances dissolved in artificial seawater, using the PPL resin, showed high extn. yield (> 85%) and the stable isotopic carbon compn. (δ13C) of these compds. was successfully recovered. These results indicate that salinity is not a parameter affecting extn. yield on PPL sorbent. For a hydrophilic compd. (atropine) the extn. efficiency was low (33%) and δ13C signature was underestimated. Size exclusion chromatog. measurements, in samples collected along a salinity gradient, demonstrate that the PPL sorbent strongly fractionates DOM. Although the DOM size class distributions in freshwaters and marine waters were initially different, their retentates were marked by similar size class distributions. This work demonstrates that PPL resin captures DOM compds. with less nitrogenous content and it seems to have a lower affinity for arom. compds. of marine origin than of terrigenous origin. The study of DOM distribution in a macro-tidal estuary demonstrated the limitations of PPL resin extn. in capturing an internal N-rich DOM prodn. event at the time of sampling. Futhermore, the isotopic compn. of the PPL resin retentate appears to depend on the extn. efficiency of the more hydrophobic compds. which changed along the salinity gradient. This study recommends careful interpretations of data that only rely on PPL extns., particularly for works tracking the origin of DOM in estuaries and comparing DOM compn. across ocean biogeochem. domains.
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    16. 16
      Spranger, T.; van Pinxteren, D.; Reemtsma, T.; Lechtenfeld, O. J.; Herrmann, H. 2D Liquid Chromatographic Fractionation with Ultra-high Resolution MS Analysis Resolves a Vast Molecular Diversity of Tropospheric Particle Organics. Environ. Sci. Technol. 2019, 53 (19), 11353– 11363,  DOI: 10.1021/acs.est.9b03839
      16
      2D Liquid Chromatographic Fractionation with Ultra-high Resolution MS Analysis Resolves a Vast Molecular Diversity of Tropospheric Particle Organics
      Spranger, Tobias; Pinxteren, Dominik van; Reemtsma, Thorsten; Lechtenfeld, Oliver J.; Herrmann, Hartmut
      Environmental Science & Technology (2019), 53 (19), 11353-11363CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A two-dimensional liq. chromatog. fractionation method was combined with direct infusion electro-spray ionization Fourier transform-ion cyclotron resonance mass spectrometry to better resolve the high complexity of org. material in atm. particles. The no. of assigned mol. formulas increased by a factor of 2.3 for a fractionated sample (18,144) compared to a bulk sample anal. without fractionation (7819), while simultaneously allowing identification of 71,240 isomeric compds. Accounting for these isomers has an impact on the means and distributions of different descriptive sample parameters. More than 15,000 compds. were exclusively identified in the fractionated sample providing insights regarding organosulfate, reduced N-contg., and polyarom. compds. formation. A method to assign organonitrates and poly-organonitrates based on Kendrick mass defect anal. is presented. This work implicated anal. sepn. led to much more detailed insights into particulate orgs. compn.; more commonly applied direct infusion mass spectrometry studies can strongly underestimate compn. complexity and lead to biased assignments of bulk org. properties. Overall, the particulate orgs. compn. is far more complex than previously shown, while sepn. by better chromatog. techniques helped to understand atm. particle constituent formation processes.
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    17. 17
      Pemberton, J. A.; Lloyd, C. E. M.; Arthur, C. J.; Johnes, P. J.; Dickinson, M.; Charlton, A. J.; Evershed, R. P. Untargeted characterisation of dissolved organic matter contributions to rivers from anthropogenic point sources using direct-infusion and high-performance liquid chromatography/Orbitrap mass spectrometry. Rapid Commun. Mass Spectrom. 2020, 34, e8618,  DOI: 10.1002/rcm.8618
      17
      Untargeted characterization of dissolved organic matter contributions to rivers from anthropogenic point sources using direct-infusion and high-performance liquid chromatography/Orbitrap mass spectrometry
      Pemberton, Jonathan A.; Lloyd, Charlotte E. M.; Arthur, Christopher J.; Johnes, Penny J.; Dickinson, Michael; Charlton, Adrian J.; Evershed, Richard P.
      Rapid Communications in Mass Spectrometry (2020), 34 (S4), e8618CODEN: RCMSEF; ISSN:0951-4198. (John Wiley & Sons Ltd.)
      Rationale : Anthropogenic org. inputs to freshwaters can exert detrimental effects on aquatic ecosystems, raising growing concern for both environmental conservation and water security. Current regulation by the EU water framework directive (European Union, 2000/60/EC) relates to org. pollution by monitoring selected micropollutants; however, aquatic ecosystem responses require a comprehensive understanding of dissolved org. matter (DOM) compn. The introduction of high-resoln. mass spectrometry (HRMS) is set to greatly increase our understanding of the compn. of DOM of both natural and anthropogenic origin derived from diffuse and point sources. Methods : DOM was extd. from riverine and treated sewage effluent using solid-phase extn. (SPE) and analyzed using dissolved org. carbon anal., direct-infusion high-resoln. mass spectrometry (DI-HRMS) and high-performance liq. chromatog. (HPLC)/HRMS. The data obtained were analyzed using univariate and multivariate statistics to demonstrate differences in background DOM, anthropogenic inputs and in-river mixing. Compd. identifications were achieved based on MS2 spectra searched against online databases. Results : DI-HRMS spectra showed the highly complex nature of all DOM SPE exts. Classification and visualization of exts. contg. many thousands of individual compds. were achieved using principal component anal. (PCA) and hierarchical cluster anal. Kruskal-Wallis analyses highlighted significant discriminating ions originating from the sewage treatment works for more in-depth investigation by HPLC/HRMS. The generation of MS2 spectra in HPLC/HRMS provided the basis for identification of anthropogenic compds. including; pharmaceuticals, illicit drugs, metabolites and oligomers, although many thousands of compds. remain unidentified. Conclusions : This new approach enables comprehensive anal. of DOM in exts. without any preconceived ideas of the compds. which may be present. This approach has the potential to be used as a high throughput, qual., screening method to det. if the compn. of point sources differs from that of the receiving water bodies, providing a new approach to the identification of hitherto unrecognised org. contribution to water bodies.
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    18. 18
      Liu, Z.; Sleighter, R. L.; Zhong, J.; Hatcher, P. G. The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry. Estuar. Coast. Shelf S. 2011, 92 (2), 205– 216,  DOI: 10.1016/j.ecss.2010.12.030
      18
      The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry
      Liu, Zhanfei; Sleighter, Rachel L.; Zhong, Junyan; Hatcher, Patrick G.
      Estuarine, Coastal and Shelf Science (2011), 92 (2), 205-216CODEN: ECSSD3; ISSN:0272-7714. (Elsevier Ltd.)
      How dissolved org. matter (DOM) undergoes chem. changes during its transit from river to ocean remains a challenge due to its complex structure. DOM along a river transect from black waters to marine waters is characterized using an offline combination of reversed-phase HPLC (RP-HPLC) coupled to electrospray ionization Fourier transform ICR mass spectrometry (ESI-FTICR-MS), as well as tandem ESI-FTICR-MS. A H2O ext. from degraded wood that mainly consists of lignins is used for comparison to the DOM from this transect. The HPLC chromatograms of all DOM samples and the wood ext. show 2 major well-sepd. components; one is hydrophilic and the other is hydrophobic, based on their elution order from the C18 column. From the FTICR-MS anal. of the HPLC fractions, the hydrophilic components mainly contain low mol. wt. compds. (< 400 Da), while the hydrophobic fractions contain the vast majority of compds. of the bulk C18 extd. DOM. The wood ext. and the DOM samples from the transect of black waters to coastal marine waters show strikingly similar HPLC chromatograms, and the FTICR-MS anal. further indicates that a large fraction of mol. formulas from these samples are the same, existing as lignin-like compds. Tandem mass spectrometry expts. show that several representative mols. from the lignin-like compds. have similar functional group losses and fragmentation patterns, consistent with modified lignin structural entities in the wood ext. and these DOM samples. Taken together, these data suggest that lignin-derived compds. may survive the transit from the river to the coastal ocean and can accumulate there because of their refractory nature.
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    19. 19
      Hawkes, J. A.; Sjoberg, P. J. R.; Bergquist, J.; Tranvik, L. J. Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry. Faraday Discuss. 2019, 218, 52– 71,  DOI: 10.1039/C8FD00222C
      19
      Complexity of dissolved organic matter in the molecular size dimension: insights from coupled size exclusion chromatography electrospray ionisation mass spectrometry
      Hawkes, J. A.; Sjoeberg, P. J. R.; Bergquist, J.; Tranvik, L. J.
      Faraday Discussions (2019), 218 (Challenges in Analysis of Complex Natural Mixtures), 52-71CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
      This paper investigates the relationship between apparent size distribution and mol. complexity of dissolved org. matter from the natural environment. We used a high pressure size exclusion chromatog. (HPSEC) method coupled to UV-Vis diode array detection (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) in order to compare the apparent size of natural org. matter, detd. by HPSEC-UV and the mol. mass detd. online by ESI-MS. We found that there was a clear discrepancy between the two methods, and found evidence for an important pool of org. matter that has a strong UV absorbance and no ESI-MS signal. Contrary to some previous research, we found no evidence that apparently high mol. wt. org. matter is constituted by aggregates of low mol. wt. (<1000 Da) material. Furthermore, our results suggest that the majority of apparent size variability within the ESI ionisable pool of org. matter is due to secondary interaction and exclusion effects on the HPSEC column, and not true differences in hydrodynamic size or intermol. aggregation.
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    20. 20
      Duarte, R. M. B. O.; Barros, A. C.; Duarte, A. C. Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography. Journal of Chromatography A 2012, 1249, 138– 146,  DOI: 10.1016/j.chroma.2012.06.022
      20
      Resolving the chemical heterogeneity of natural organic matter: New insights from comprehensive two-dimensional liquid chromatography
      Duarte, Regina M. B. O.; Barros, Ana C.; Duarte, Armando C.
      Journal of Chromatography A (2012), 1249 (), 138-146CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
      For the purpose of resolving the chem. heterogeneity of natural org. matter (NOM), comprehensive two-dimensional liq. chromatog. (LC × LC) was employed for the first time to map the hydrophobicity vs. mol. wt. (MW) distribution of two well-known complex org. mixts.: Suwannee River Fulvic Acids (SR-FA) and Pony Lake Fulvic Acids (PL-FA). Two methods have been developed using either a conventional reversed-phase (RP) silica column or a mixed-mode hydrophilic interaction column operating under aq. RP mode in the first dimension, and a size-exclusion column in the second dimension. The LC × LC fractions were screened online by UV at 254 nm, mol. fluorescence at excitation/emission wavelengths (λ Exc/λ Em) of 240/450 nm, and by evaporative light scattering. The MW distributions of these two NOM samples were further characterized by no. (Mn) and wt. (Mw) av. MW, and by polydispersity (Mw/Mn). Findings suggest that the combination of two independent sepn. mechanisms is promising in extend the range of NOM sepn. For the cases where NOM sepn. was accomplished, smaller Mw group fractions seem to be related to a more hydrophobic nature. Regardless of the detection method, the complete range of MW distribution provided by both comprehensive LC × LC methods was found to be lower than those reported in the literature.
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    21. 21
      Petras, D.; Koester, I.; Da Silva, R.; Stephens, B. M.; Haas, A. F.; Nelson, C. E.; Kelly, L. W.; Aluwihare, L. I.; Dorrestein, P. C. High-Resolution Liquid Chromatography Tandem Mass Spectrometry Enables Large Scale Molecular Characterization of Dissolved Organic Matter. Frontiers in Marine Science 2017, 4, 405,  DOI: 10.3389/fmars.2017.00405
      There is no corresponding record for this reference.
    22. 22
      Rowland, S. M.; Smith, D. F.; Blakney, G. T.; Corilo, Y. E.; Hendrickson, C. L.; Rodgers, R. P. Online Coupling of Liquid Chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry at 21 T Provides Fast and Unique Insight into Crude Oil Composition. Anal. Chem. 2021, 93 (41), 13749– 13754,  DOI: 10.1021/acs.analchem.1c01169
      22
      Online Coupling of Liquid Chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry at 21 T Provides Fast and Unique Insight into Crude Oil Composition
      Rowland, Steven M.; Smith, Donald F.; Blakney, Gregory T.; Corilo, Yuri E.; Hendrickson, Christopher L.; Rodgers, Ryan P.
      Analytical Chemistry (Washington, DC, United States) (2021), 93 (41), 13749-13754CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      High magnetic field Fourier transform ICR (FT-ICR) mass spectrometry provides the highest mass resolving power and mass measurement accuracy for detailed characterization of complex chem. mixts. Here, the authors report the coupling of online liq. chromatog. of complex mixts. with a 21 T FT-ICR mass spectrometer. The high magnetic field enables large ion populations to be analyzed for each spectrum for a high dynamic range, with 3.2 million mass resolving power at m/z 400 (6.2 s transient duration) or 1.6 million (3.1 s transient duration) while maintaining high mass accuracy for mol. formula assignment (root-mean-square assignment error < 0.150 ppm). Thousands of unique elemental compns. are assigned per mass spectrum, which can be grouped by the heteroatom class, double bond equiv. (the no. of rings and double bonds to C), and C no. Figures of merit are discussed, as well as characterization of an Arabian heavy vacuum gas oil in terms of the ring no., compd. class, double bond equiv., and ion type. Consideration of elemental compn. and retention order provides addnl. structural information.
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    23. 23
      Patriarca, C.; Bergquist, J.; Sjoberg, P. J. R.; Tranvik, L.; Hawkes, J. A. Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples. Environ. Sci. Technol. 2018, 52 (4), 2091– 2099,  DOI: 10.1021/acs.est.7b04508
      23
      Online HPLC-ESI-HRMS Method for the Analysis and Comparison of Different Dissolved Organic Matter Samples
      Patriarca, Claudia; Bergquist, Jonas; Sjoeberg, Per J. R.; Tranvik, Lars; Hawkes, Jeffrey A.
      Environmental Science & Technology (2018), 52 (4), 2091-2099CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Natural dissolved org. matter (DOM) is an ultracomplex mixt. that is essential to global carbon cycling but is poorly understood because of its complexity. The most powerful tool for the DOM characterization is high-resoln. mass spectrometry (HRMS) generally combined to direct infusion (DI) as sample introduction. Liq. chromatog. (LC) represents a compelling alternative to DI; however, state-of-the-art techniques involve only offline LC-HRMS approaches, which have important logistical drawbacks that make DOM anal. more challenging. This study introduces a new method based on online coupling of liq. chromatog. to high resoln. mass spectrometry, able to overcome the disadvantages of usual approaches. It is characterized by high reproducibility (% Bray-Curtis dissimilarity among replicates ≈ 2.5%), and it reduces transient complexity and contaminant interferences, thus increasing the signal-to-noise ratio (S/N), leading to the identification of an overall larger no. of formulas in the mixt. Moreover, the application of an in silico fractionation prior to the statistical anal. allows an easy, flexible, fast, and detailed comparison of DOM samples from a variety of sources with a single chromatog. run.
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    24. 24
      Sandron, S.; Rojas, A.; Wilson, R.; Davies, N. W.; Haddad, P. R.; Shellie, R. A.; Nesterenko, P. N.; Kelleher, B. P.; Paull, B. Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter. Environmental Science-Processes & Impacts 2015, 17 (9), 1531– 1567,  DOI: 10.1039/C5EM00223K
      24
      Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter
      Sandron, Sara; Rojas, Alfonso; Wilson, Richard; Davies, Noel W.; Haddad, Paul R.; Shellie, Robert A.; Nesterenko, Pavel N.; Kelleher, Brian P.; Paull, Brett
      Environmental Science: Processes & Impacts (2015), 17 (9), 1531-1567CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)
      This review presents an overview of the sepn. techniques applied to the complex challenge of dissolved org. matter characterization. The review discusses methods for isolation of dissolved org. matter from natural waters, and the range of sepn. techniques used to further fractionate this complex material. The review covers both liq. and gas chromatog. techniques, in their various modes, and electrophoretic based approaches. For each, the challenges that the sepn. and fractionation of such an immensely complex sample poses is critically reviewed.
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    25. 25
      Jennings, E.; Kremser, A.; Han, L.; Reemtsma, T.; Lechtenfeld, O. J. Discovery of Polar Ozonation Byproducts via Direct Injection of Effluent Organic Matter with Online LC-FT-ICR-MS. Environ. Sci. Technol. 2022, 56 (3), 1894– 1904,  DOI: 10.1021/acs.est.1c04310
      25
      Discovery of polar ozonation byproducts via direct injection of effluent organic matter with online LC-FT-ICR-MS
      Jennings, Elaine; Kremser, Arina; Han, Limei; Reemtsma, Thorsten; Lechtenfeld, Oliver J.
      Environmental Science & Technology (2022), 56 (3), 1894-1904CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      Effluent org. matter (EfOM), a major ozone consumer during wastewater ozonation, is a complex mixt. of natural and anthropogenic org. mols. Ozonation of EfOM adds to mol. complexity by introducing polar and potentially mobile ozonation byproducts (OBPs). Currently, nontargeted direct infusion (DI) ultrahigh resoln. mass spectrometry (e.g. FT-ICR-MS) is used to study OBPs but requires sample extn., limiting the accessible polarity range of OBPs. To better understand the impact of ozonation on EfOM and the formation of polar OBPs, nonextd. effluent was analyzed by direct injection onto a reversed-phase liq. chromatog. system (RP-LC) online hyphenated with an FT-ICR-MS. Over four times more OBPs were detected in nonextd. EfOM compared to effluent extd. with solid phase extn. and measured with DI-FT-ICR-MS (13817 vs 3075). Over 1500 highly oxygenated OBPs were detected exclusively in early eluting fractions of nonextd. EfOM, indicating polar OBPs. Oxygenation of these newly discovered OBPs is higher than previously found, with an av. mol. DBE-O value of -3.3 and O/C ratio of 0.84 in the earliest eluting OBP fractions. These polar OBPs are consistently lost during extn. but may play an important role in understanding the environmental impact of ozonated EfOM. Moreover, 316 mol. formulas classified as nonreactive to ozone in DI-FT-ICR-MS can be identified with LC-FT-ICR-MS as isomers with varying degrees of reactivity, providing for the first time exptl. evidence of differential reactivity of complex org. matter isomers with ozone.
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    26. 26
      Flerus, R.; Koch, B. P.; Schmitt-Kopplin, P.; Witt, M.; Kattner, G. Molecular level investigation of reactions between dissolved organic matter and extraction solvents using FT-ICR MS. Marine Chemistry 2011, 124, 100– 107,  DOI: 10.1016/j.marchem.2010.12.006
      26
      Molecular level investigation of reactions between dissolved organic matter and extraction solvents using FT-ICR MS
      Flerus, Ruth; Koch, Boris P.; Schmitt-Kopplin, Philippe; Witt, Matthias; Kattner, Gerhard
      Marine Chemistry (2011), 124 (1-4), 100-107CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
      The investigation of marine dissolved org. matter (DOM) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) requires the concn. and extn. of the DOM. Reactions between extn. solvent and DOM might influence data evaluation parameters, which are used to compare DOM of different origin. Potential reactions between methanol and solid-phase extd. marine DOM (SPE-DOM) and their influence on FT-ICR MS data were studied on a mol. level. For elemental formula assignments 9 isotopes were included in the evaluation, and different strategies based on isotope ratios and mass peak intervals were applied to achieve data sets of single assignments. DOM was eluted from the sorbent with methanol, methanol-13C-D4 and acetonitrile and stored at 20 °C and - 20 °C. Under both storage conditions H/D exchanges were detected. In addn., esterifications were detected in the ext. stored at 20 °C, but did not result in significant differences in the mass peak magnitudes. Hence, no changes of the weighted av. H/C and O/C ratios or other values such as Kendrick mass defect (KMD) and double bond equiv. (DBE) were obsd. Acetonitrile was tested as an alternative solvent. Both, methanol or acetonitrile can be used to ext. marine DOM from sorbents if samples are immediately stored at - 20 °C after the SPE process. However, FT-ICR MS data of DOM samples extd. with different solvents showed substantial differences as expected and should not be directly compared.
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    27. 27
      Longnecker, K. Dissolved organic matter in newly formed sea ice and surface seawater. Geochim. Cosmochim. Acta 2015, 171, 39– 49,  DOI: 10.1016/j.gca.2015.08.014
      27
      Dissolved organic matter in newly formed sea ice and surface seawater
      Longnecker, Krista
      Geochimica et Cosmochimica Acta (2015), 171 (), 39-49CODEN: GCACAK; ISSN:0016-7037. (Elsevier Ltd.)
      Changes in sea ice in the Arctic will have ramifications on regional and global carbon cycling. Research to date has primarily focused on the regional impacts to biol. activity and global impacts on atm. processes. The current project considers the mol.-level compn. of org. carbon within sea ice compared to the org. matter in seawater. The project revealed that the compn. of org. matter within sea ice was more variable than the compn. of org. matter within the surface ocean. Furthermore, sea ice samples presented two distinct patterns in the compn. of org. matter with a portion of the sea ice samples contg. protein-like org. matter. Yet, the samples were collected in the early winter period when little biol. activity is expected. Thus, one hypothesis is that phys. processes acting during the formation of sea ice selectively transferred org. matter from seawater into sea ice. The present project expands our understanding of dissolved org. matter in sea ice and surface seawater and thereby increases our knowledge of carbon cycling in polar regions.
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    28. 28
      Han, L.; Kaesler, J.; Peng, C.; Reemtsma, T.; Lechtenfeld, O. J. Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions. Anal. Chem. 2021, 93 (3), 1740– 1748,  DOI: 10.1021/acs.analchem.0c04426
      28
      Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions
      Han, Limei; Kaesler, Jan; Peng, Chang; Reemtsma, Thorsten; Lechtenfeld, Oliver J.
      Analytical Chemistry (Washington, DC, United States) (2021), 93 (3), 1740-1748CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Natural org. matter (NOM) is a highly complex mixt. of natural org. mols. The recent developments in NOM mol. characterization methods have shown that ESI-FT-ICR hyphenated with liq. chromatog. (LC) is a promising approach to also obtain chem. information (such as polarity and mol. size) about NOM mols. However, due to changing solvent compn. during gradient elution in LC-FT-ICR-MS, ionization conditions also change throughout the chromatog. sepn. process. In this study, we applied a post-LC column counter gradient (CG) to ensure stable solvent conditions for transient ESI-MS signals. Suwanee River Fulvic Acid (SRFA) std. and a peat pore water were used as representative dissolved NOM samples for method development and validation. Our results show that in polar NOM fractions (which elute with <50% methanol) the TIC intensity and no. of assigned mol. formulas were increased by 48% and 20%, as compared to the std. gradient (SG) method. Further application of a Q-isolation and selective ion accumulation for low abundance fractions revealed over 3 times more mol. formulas (esp. for CHNO, CHOS, CHNOS formula classes) than in full scan mode. The no. of detected highly polar NOM compds. (with elemental ratios H/C < 1, O/C > 0.6) were more than 20 times larger for CG-LC mode as compared to direct infusion (DI) (5715 vs 266 MF). We conclude that the application of a postcolumn counter gradient in LC-FT-ICR-MS analyses of NOM offers novel insight into the most polar fractions of NOM which are inaccessible in conventional DI measurements.
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    29. 29
      Lechtenfeld, O. J.; Koch, B. P.; Gašparović, B.; Frka, S.; Witt, M.; Kattner, G. The influence of salinity on the molecular and optical properties of surface microlayers in a karstic estuary. Marine Chemistry 2013, 150, 25– 38,  DOI: 10.1016/j.marchem.2013.01.006
      29
      The influence of salinity on the molecular and optical properties of surface microlayers in a karstic estuary
      Lechtenfeld, Oliver J.; Koch, Boris P.; Gasparovic, Blazenka; Frka, Sanja; Witt, Matthias; Kattner, Gerhard
      Marine Chemistry (2013), 150 (), 25-38CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
      Sea-surface microlayers and the corresponding underlying waters of the karstic Krka Estuary (Croatia) were studied with respect to optical and mol. properties of dissolved org. matter (DOM). Solid-phase extd. DOM was sepd. by reversed-phase chromatog. and analyzed with ultra-high resoln. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The no. and summed magnitudes of FT-ICR MS peaks, enriched in the microlayer, increased with increasing salinity along the estuary. The mol. H to C ratio (as a measure of polarity) of enriched compds. was higher for the low salinity samples than for a high salinity marine station, which we propose is a consequence of a salt-mediated sepn. mechanism. Absorption and fluorescence of all samples decreased along the estuary with the microlayer samples showing higher absorption than the underlying water. Chromatog. and FT-ICR MS data revealed a distinct shift towards a smaller mol. size in the microlayer compared to the underlying water. The redistribution of dissolved org. carbon within chromatog. fractions and the decrease in mol. size was interpreted to result from photodegrdn. and/or microbial reprocessing. Collision induced dissocn. of selected FT-ICR MS mass peaks revealed the presence of S-contg. anthropogenic surfactants enriched in the microlayer. Mol. level study of estuarine surface microlayers will help to better understand the highly dynamic character of these systems, the accumulation of natural org. matter and anthropogenic pollutants and the role of surface microlayers for the sea-air energy exchange.
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    30. 30
      Kim, S.; Kramer, R. W.; Hatcher, P. G. Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the van Krevelen diagram. Anal. Chem. 2003, 75 (20), 5336– 44,  DOI: 10.1021/ac034415p
      30
      Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the Van Krevelen diagram
      Kim, Sunghwan; Kramer, Robert W.; Hatcher, Patrick G.
      Analytical Chemistry (2003), 75 (20), 5336-5344CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool in the study of natural org. matter (NOM) at the mol. level.1 Ultrahigh-resoln. ESI-MS analyses of NOM often produce very complicated spectra; therefore, visual presentation and structural interpretations of the spectra are difficult. To meet this anal. challenge, we herein propose and demonstrate an approach using the van Krevelen diagram. With this approach, complicated mass spectra can be visualized in a way that allows for (1) possible reaction pathways to be identified and presented, and (2) qual. analyses on major classes of compds. that comprise ultrahigh-resoln. spectra. The qual. analyses are in a good agreement with results obtained from analyses by other anal. techniques. Addnl., the van Krevelen diagram can be expanded to a 3D plot by using peak intensities or relative intensities as the z-axis. The 3D van Krevelen diagram allows for an evaluation of the relative significance of structurally related compds. The 3D plot can also be a useful tool for compositional differentiation among samples.
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    31. 31
      Flerus, R.; Lechtenfeld, O. J.; Koch, B. P.; McCallister, S. L.; Schmitt-Kopplin, P.; Benner, R.; Kaiser, K.; Kattner, G. A molecular perspective on the ageing of marine dissolved organic matter. Biogeosciences 2012, 9 (6), 1935– 1955,  DOI: 10.5194/bg-9-1935-2012
      31
      A molecular perspective on the ageing of marine dissolved organic matter
      Flerus, R.; Lechtenfeld, O. J.; Koch, B. P.; McCallister, S. L.; Schmitt-Kopplin, P.; Benner, R.; Kaiser, K.; Kattner, G.
      Biogeosciences (2012), 9 (6), 1935-1955CODEN: BIOGGR; ISSN:1726-4170. (Copernicus Publications)
      Dissolved org. matter (DOM) was extd. by solid-phase extn. (SPE) from 137 water samples from different climate zones and different depths along an eastern Atlantic Ocean transect. The exts. were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). Δ14C analyses were performed on subsamples of the SPE-DOM. In addn., the amt. of dissolved org. carbon was detd. for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were obsd. between the magnitudes of 43% of the FT-ICR mass peaks and the ext. Δ14C values. Decreasing SPE-DOM Δ14C values went along with a shift in the mol. compn. to higher av. masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM Δ14C distribution for all 137 samples. Based on single mass peaks, a degrdn. index (IDEG) was developed to compare the degrdn. state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between Δ14C, IDEG, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. DOM weighted normalized mass peak magnitudes were used to compare aged and recent SPE-DOM on a semi-quant. mol. basis. The magnitude comparison showed a continuum of different degrdn. rates for the detected compds. A high proportion of the compds. should persist, possibly modified by partial degrdn., in the course of thermohaline circulation. Prokaryotic (bacterial) prodn., transformation and accumulation of this very stable DOM occur primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that prodn. and degrdn. are dynamic processes.
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    32. 32
      Medeiros, P. M.; Seidel, M.; Niggemann, J.; Spencer, R. G. M.; Hernes, P. J.; Yager, P. L.; Miller, W. L.; Dittmar, T.; Hansell, D. A. A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean. Global Biogeochem. Cycles 2016, 30 (5), 689– 699,  DOI: 10.1002/2015GB005320
      32
      A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean
      Medeiros, Patricia M.; Seidel, Michael; Niggemann, Jutta; Spencer, Robert G. M.; Hernes, Peter J.; Yager, Patricia L.; Miller, William L.; Dittmar, Thorsten; Hansell, Dennis A.
      Global Biogeochemical Cycles (2016), 30 (5), 689-699CODEN: GBCYEP; ISSN:1944-9224. (Wiley-Blackwell)
      Marine dissolved org. matter (DOM) contains one of the largest exchangeable org. carbon pools on Earth. Riverine input represents an important source of DOM to the oceans, yet much remains to be learned about the fate of the DOM linking terrestrial to oceanic carbon cycles through rivers at the global scale. Here we use ultrahigh-resoln. mass spectrometry to identify 184 mol. formulas that are indicators of riverine inputs (referred to as t-Peaks) and to track their distribution in the deep North Atlantic and North Pacific Oceans. The t-Peaks were found to be enriched in the Amazon River, to be highly correlated with known tracers of terrigenous input, and to be obsd. in all samples from four different rivers characterized by vastly different landscapes and vegetation coverage spanning equatorial (Amazon and Congo), subtropical (Altamaha), and Arctic (Kolyma) regions. Their distribution reveals that terrigenous org. matter is injected into the deep ocean by the global meridional overturning circulation, indicating that a fraction of the terrigenous DOM introduced by rivers contributes to the DOM pool obsd. in the deep ocean and to the storage of terrigenous org. carbon. This novel mol. approach can be used to further constrain the transfer of DOM from land to sea, esp. considering that Fourier transform ion cyclotron resonance mass spectrometer anal. is becoming increasingly frequent in studies characterizing the mol. compn. of DOM in lakes, rivers, and the ocean.
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    33. 33
      Koch, B. P.; Ludwichowski, K.-U.; Kattner, G.; Dittmar, T.; Witt, M. Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS. Mar. Chem. 2008, 111 (3–4), 233– 241,  DOI: 10.1016/j.marchem.2008.05.008
      33
      Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS
      Koch, Boris P.; Ludwichowski, Kai-Uwe; Kattner, Gerhard; Dittmar, Thorsten; Witt, Matthias
      Marine Chemistry (2008), 111 (3-4), 233-241CODEN: MRCHBD; ISSN:0304-4203. (Elsevier B.V.)
      Marine dissolved org. matter (DOM) was sepd. by reversed-phase (RP) liq. chromatog. method and analyzed with fluorescence/absorption detection and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). The three key characteristics of the RP method are: (a) the C18-RP column chosen provides enhanced sepn. when the aq. phase is 100% buffer-free water, and it does not degrade over time; (b) the water eluent adjusted to pH 7 significantly improves the resoln. of water sol. compds.; (c) the initial flow maintained at low levels improves the sepn. of polar compds. In samples, contg. fresh DOM, specific peaks were detected, which were absent in old DOM samples. The combination with size exclusion chromatog. (SEC) also demonstrated the relation between polarity and mol. size of DOM. FT-ICR-MS was applied to evaluate the quality of sepn. on a mol. scale demonstrating that physico-chem. characteristics of DOM can be related to mol. formulas. Sample exts. were sepd. into 4 preparative fractions, and a large suite of the identified mol. formulas only occurred in specific fractions. This is an important basis for the application of further anal. techniques in order to perform a more target-oriented anal. aiming at the detn. of source and process biomarkers for DOM.
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    34. 34
      Kim, D.; Kim, S.; Son, S.; Jung, M. J.; Kim, S. Application of Online Liquid Chromatography 7 T FT-ICR Mass Spectrometer Equipped with Quadrupolar Detection for Analysis of Natural Organic Matter. Anal. Chem. 2019, 91 (12), 7690– 7697,  DOI: 10.1021/acs.analchem.9b00689
      34
      Application of Online Liquid Chromatography 7 T FT-ICR Mass Spectrometer Equipped with Quadrupolar Detection for Analysis of Natural Organic Matter
      Kim, Donghwi; Kim, Sungjune; Son, Seungwoo; Jung, Maeng-Joon; Kim, Sunghwan
      Analytical Chemistry (Washington, DC, United States) (2019), 91 (12), 7690-7697CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with quadrupolar detection (QPD), was applied for online liq. chromatog. (LC) MS anal. of natural org. matter (NOM). Although FT-ICR MS has emerged as an important anal. technique to study NOM, there are few previous reports on online LC FT-ICR MS anal. of NOM due to the long acquisition time (2-8 s) required to obtain high-resoln. mass spectra. The QPD technique provides a crit. advantage over the conventional dipolar detection (DPD) technique for LC-MS anal. because a spectrum with the same resolving power can be obtained in approx. half the acquisition time. QPD FT-ICR MS provides resolving powers ((m/(Δm50%))) of ∼300000 and 170000 at m/z 400 with acquisition times per scan of 1.2 and 0.8 s, resp. The reduced acquisition time per scan allows increased no. of acquisitions in a given LC anal. time, resulting in improved signal to noise (S/N) ratio and dynamic range in comparison to conventional methods. For example, 40% and 100% increases in the no. of detected peaks were obtained with LC QPD FT-ICR MS, in comparison to conventional LC DPD FT-ICR MS and direct-injection FT-ICR MS. It is also possible to perform more quant. comparison and mol. level investigation of NOMs with 2 μg of a NOM sample. The data presented herein demonstrate a proof of principle that QPD combined with LC FT-ICR MS is a sensitive anal. technique that can provide comprehensive information about NOM.
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    35. 35
      Hawkes, J. A.; Patriarca, C.; Sjöberg, P. J. R.; Tranvik, L. J.; Bergquist, J. Extreme isomeric complexity of dissolved organic matter found across aquatic environments. Limnology and Oceanography Letters 2018, 3 (2), 21– 30,  DOI: 10.1002/lol2.10064
      35
      Extreme isomeric complexity of dissolved organic matter found across aquatic environments
      Hawkes, Jeffrey A.; Patriarca, Claudia; Sjoeberg, Per J. R.; Tranvik, Lars J.; Bergquist, Jonas
      Limnology & Oceanography Letters (2018), 3 (2), 21-30CODEN: LOLIBT; ISSN:2378-2242. (John Wiley & Sons Ltd.)
      The natural aquatic environment contains an enormous pool of dissolved reduced carbon, present as ultra-complex mixts. that are constituted by an unknown no. of compds. at vanishingly small concns. We attempted to sep. individual structural isomers from several samples using online reversed-phase chromatog. with selected ion monitoring/tandem mass spectrometry, but found that isomeric complexity still presented a boundary to investigation even after chromatog. simplification of the samples. However, it was possible to det. that the structural complexity differed among samples. Our results also suggest that extreme structural complexity was a ubiquitous feature of dissolved org. matter (DOM) in all aquatic systems, meaning that this diversity may play similar roles for recalcitrance and degrdn. of DOM in all tested environments.
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    36. 36
      Felgate, S. L.; Craig, A. J.; Moodie, L. W. K.; Hawkes, J. Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522). Anal. Chem. 2023, 95 (16), 6559– 6567,  DOI: 10.1021/acs.analchem.2c05304
      36
      Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522)
      Felgate, Stacey L.; Craig, Alexander J.; Moodie, Lindon W. K.; Hawkes, Jeffrey
      Analytical Chemistry (Washington, DC, United States) (2023), 95 (16), 6559-6567CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Recent methodol. advances have greatly increased our ability to characterize aquatic dissolved org. matter (DOM) using high-resoln. instrumentation, including NMR (NMR) and mass spectrometry (HRMS). Reliable DOM ref. materials are required for further method development and data set alignment but do not currently exist for the marine environment. This presents a major limitation for marine biogeochem. and related fields, including natural product discovery. To fill this resource gap, we have prepd. a coastal marine DOM ref. material (TRM-0522) from 45 m deep seawater obtained ~ 1 km offshore of Sweden's west coast. Over 3000 mol. formulas were assigned by direct infusion HRMS, confirming sample diversity, and the distribution of formulas in van Krevelen space was typical for a marine sample, with the majority of formulas in the region H/C 1-1.5 and O/C 0.3-0.7. The extd. DOM pool was more nitrogen (N)- and sulfur (S)-rich than a typical terrestrial ref. material (SRFA). MZmine3 processing of ultrahigh-performance liq. chromatog. (UPLC)-HRMS/MS data revealed 494 resolvable features (233 in neg. mode; 261 in pos. mode) over a wide range of retention times and masses. NMR data indicated low contributions from arom. protons and, generally speaking, low lignin, humic, and fulvic substances assocd. with terrestrial samples. Instead, carboxylic-rich aliph. mols. were the most abundant components, followed by carbohydrates and aliph. functionalities. This is consistent with a very low specific UV absorbance SUVA254 value of 1.52 L mg C-1 m-1. When combined with comparisons with existing terrestrial ref. materials (Suwannee River fulvic acid and Pony Lake fulvic acid), these results suggest that TRM-0522 is a useful and otherwise unavailable ref. material for use in marine DOM biogeochem.
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    37. 37
      Lohse, M.; Blaser, S.; Vetterlein, D.; Schluter, S.; Oburger, E.; Reemtsma, T.; Lechtenfeld, O. J. Online Nano Solid Phase Extraction Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry Workflow to Analyze Small Scale Gradients of Soil Solution Organic Matter in the Rhizosphere. Anal. Chem. 2020, 92 (15), 10442– 10449,  DOI: 10.1021/acs.analchem.0c00946
      37
      Online Nano Solid Phase Extraction Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry Workflow to Analyze Small Scale Gradients of Soil Solution Organic Matter in the Rhizosphere
      Lohse, M.; Blaser, S. R. G. A.; Vetterlein, D.; Schlueter, S.; Oburger, E.; Reemtsma, T.; Lechtenfeld, O. J.
      Analytical Chemistry (Washington, DC, United States) (2020), 92 (15), 10442-10449CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      A new method combining online nano solid phase extn. coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was developed to ext. and analyze org. matter (OM) from microliter vols. of salt contg. soil soln. samples. This approach allows the reproducible anal. of only minute amts. of org. carbon (down to 10 ng C) without the need of further sample prepn. The new method was applied to unravel developing small-scale patterns of dissolved org. matter (DOM) in soil solns. of a soil column expt. in which Zea mays plants were grown for 3 wk. Soil soln. was sampled by micro suction cups from the undisturbed soil-root system once a week. Growth of the root system and, hence, position of individual roots relative to the suction cups was followed by X-ray computed tomog. (X-ray CT). Our method makes it possible to resolve the chem. complexity of soil soln. OM (up to 4300 mol. formulas from 2.5μL sample). This allows to observe chem. gradients in the rhizosphere on a mol. level over time. The increasing influence of roots on soil soln. OM is visible from higher mol. masses, an increasing degree of oxygenation and a higher fraction of formulas contg. heteroatoms. The online nano solid phase extn.-FT-ICR-MS method provides novel insight into the processes affecting DOM in the rhizosphere, such as root exudation, microbial processes, and soil org. matter stabilization.
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    38. 38
      De Nicolo, A.; Cantu, M.; D’Avolio, A. Matrix effect management in liquid chromatography mass spectrometry: the internal standard normalized matrix effect. Bioanalysis 2017, 9 (14), 1093– 1105,  DOI: 10.4155/bio-2017-0059
      38
      Matrix effect management in liquid chromatography mass spectrometry: the internal standard normalized matrix effect
      De Nicolo, Amedeo; Cantu, Marco; D'Avolio, Antonio
      Bioanalysis (2017), 9 (14), 1093-1105CODEN: BIOAB4; ISSN:1757-6180. (Future Science Ltd.)
      LC-MS is becoming a std. for many applications, thanks to high sensitivity and selectivity; nevertheless, some issues are still present, particularly due to matrix effect (ME). Considering this, the use of optimal internal stds. (ISs, usually stable-isotope labeled) is important, but not always possible because of cost or availability. Therefore, a deep investigation of the inter-lot variability of the ME and of the correcting power of the chosen IS (isotope-labeled or not) is mandatory. While the adoption of isotopically labeled ISs considered as a 'gold std.' to mitigate ME impact on anal. results, there is not consensus about the std. technique to evaluate it during method validation. In this paper, currently available techniques to evaluate, reduce or counterbalance ME are presented and discussed. Finally, these techniques were summarized in a flowchart for a robust management of ME, particularly considering the concept of 'internal std. normalized ME'.
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    39. 39
      da Silva, M. P.; Koch, B. P.; von Tümpling, W.; Herzsprung, P.; Kamjunke, N.; Reemtsma, T.; Schmitt-Kopplin, P.; Lechtenfeld, O. J. A guideline for the application of correlation analyses based on ultra-high resolution mass spectra of natural organic matter: The impact of intensity normalization methods. Submitted for publication.
      There is no corresponding record for this reference.
    40. 40
      Sleighter, R. L.; Chen, H.; Wozniak, A. S.; Willoughby, A. S.; Caricasole, P.; Hatcher, P. G. Establishing a measure of reproducibility of ultrahigh-resolution mass spectra for complex mixtures of natural organic matter. Anal. Chem. 2012, 84 (21), 9184– 91,  DOI: 10.1021/ac3018026
      40
      Establishing a Measure of Reproducibility of Ultrahigh-Resolution Mass Spectra for Complex Mixtures of Natural Organic Matter
      Sleighter, Rachel L.; Chen, Hongmei; Wozniak, Andrew S.; Willoughby, Amanda S.; Caricasole, Paolo; Hatcher, Patrick G.
      Analytical Chemistry (Washington, DC, United States) (2012), 84 (21), 9184-9191CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      This study describes a method for evaluating the reproducibility of replicate mass spectra acquired for complex natural org. matter (NOM) samples analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, with regard to both peak detection and peak magnitude. Because studies of NOM characterization utilize not only the emergence and disappearance of peaks but also changes in relative peak magnitude, it is important to establish that the differences between samples are significantly larger than those between sample replicates. Here, a method is developed for correcting strict signal-to-noise thresholds, along with a new scheme for assessing the reproducibility of peak magnitudes. Furthermore, a systematic approach for discerning when the comparison of samples by the presence or absence of peaks is appropriate and when it is necessary to compare based on the relative magnitude of the peaks is presented. A variety of 10 different types of NOM samples are analyzed in duplicate or triplicate instrumental injections or exptl. extns. A framework for these procedures is provided, and acceptable reproducibility levels are recommended.
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    41. 41
      Moran, X. A. G.; Gasol, J. M.; Arin, L.; Estrada, M. A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production. Marine Ecology-Progress Series 1999, 187, 31– 41,  DOI: 10.3354/meps187031
      41
      A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production
      Moran, Xose A. G.; Gasol, Josep M.; Arin, Laura; Estrada, Marta
      Marine Ecology: Progress Series (1999), 187 (), 31-41CODEN: MESEDT; ISSN:0171-8630. (Inter-Research)
      The performance of 2 types of glass fiber filters (GF/F: 0.7 μm; GF/C: 1.2 μm) and 2 membrane filters (PC0.2: polycarbonate 0.2 μm; CE0.22: mixed cellulose esters 0.22 μm) was tested in estg. chlorophyll a and primary prodn. with the 14C technique. Expts. were carried out with water samples from the NW Mediterranean, the NE Atlantic, and the Antarctic Ocean. The first expt. compared measurements of particulate org. C (POC) prodn. whereas the other 3 also considered total (TOC) and dissolved (DOC) C fixation. No significant differences among filters were found regarding chlorophyll a retention but large discrepancies existed in the amt. of labeled org. C retained in all the expts. Both types of glass fiber filters, esp. GF/F, yielded higher values of apparent PO14C recovery than the membrane filters. The GF/F-derived POC prodn. rates were up to twice the PC0.2-derived rates and 63% higher than CE0.22-derived ones. The estd. rates of phytoplanktonic DOC prodn. were higher with the membrane filters in comparison to the GF/F ones. This discrepancy was attributed to a high DO14C adsorption to the glass fibers of GF filters. Due to uncertainties in the magnitude of this process in other samples, it is concluded that GF filters are not suitable when particulate primary prodn. must be measured without interference of released dissolved products, and that membrane filters should be used instead.
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    42. 42
      Halewood, E.; Opalk, K.; Custals, L.; Carey, M.; Hansell, D. A.; Carlson, C. A. Determination of dissolved organic carbon and total dissolved nitrogen in seawater using High Temperature Combustion Analysis. Frontiers in Marine Science 2022, 9, 1061646,  DOI: 10.3389/fmars.2022.1061646
      There is no corresponding record for this reference.
    43. 43
      Fonvielle, J. A.; Felgate, S. L.; Tanentzap, A. J.; Hawkes, J. A. Assessment of sample freezing as a preservation technique for analysing the molecular composition of dissolved organic matter in aquatic systems. RSC Adv. 2023, 13 (35), 24594– 24603,  DOI: 10.1039/D3RA01349A
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      Assessment of sample freezing as a preservation technique for analysing the molecular composition of dissolved organic matter in aquatic systems
      Fonvielle, Jeremy A.; Felgate, Stacey L.; Tanentzap, Andrew J.; Hawkes, Jeffrey A.
      RSC Advances (2023), 13 (35), 24594-24603CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      Dissolved org. matter (DOM) is widely studied in environmental and biogeochem. sciences, but is susceptible to chem. and biol. degrdn. during sample transport and storage. Samples taken in remote regions, aboard ships, or in large nos. need to be preserved for later anal. without changing DOM compn. Here we compare high-resoln. mass spectra of solid phase extractable DOM before and after freezing at -20°C. We found that freezing increases compositional dissimilarity in DOM by between 0 to 18.2% (median = 2.7% across 7 sites) when comparing replicates that were frozen vs. unfrozen, i.e., processed immediately after sampling, as compared with differences between unfrozen replicates. The effects of freezing primarily consisted of a poorer detection limit, but were smaller than other sample prepn. and anal. steps, such as solid phase extn. and variable ionisation efficiency. Freezing samples for either 21 or 95 days led to similar and only slight changes in DOM compn., albeit with more variation for the latter. Therefore, we conclude that sample freezing on these time scales should not impede scientific study of aquatic DOM and can be used where it makes logistical sense, such as for large spatial surveys or study of archived samples.
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    44. 44
      Reemtsma, T.; Alder, L.; Banasiak, U. A multimethod for the determination of 150 pesticide metabolites in surface water and groundwater using direct injection liquid chromatography-mass spectrometry. J. Chromatogr A 2013, 1271 (1), 95– 104,  DOI: 10.1016/j.chroma.2012.11.023
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      A multimethod for the determination of 150 pesticide metabolites in surface water and groundwater using direct injection liquid chromatography-mass spectrometry
      Reemtsma, Thorsten; Alder, Lutz; Banasiak, Ursula
      Journal of Chromatography A (2013), 1271 (1), 95-104CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
      Based on available information for 293 pesticides (herbicides, insecticides, fungicides, biocides, growth regulators), 210 pesticide metabolites were selected for inclusion in a multi-method for groundwater and surface water anal. With the final method, 150 pesticide metabolites can be analyzed in groundwater and surface water by direct injection liq. chromatog./electro-spray ionization/tandem mass spectrometry with multiple-reaction monitoring. For most metabolites this is the first published anal. method. For all metabolites, linear calibration in drinking water was possible, with a lower limits of calibration, 0.1 μg/L, achieved for 142 analytes and 0.01 μg/L for 113 analytes. Matrix effects in groundwater and surface water compared to those in drinking water were moderate (±20%) for 87% of analytes. For crit. sample/analyte combinations, std. addn. must be used for correct quantification. This method allows an extensive study of the occurrence of previously unknown or undetectable pesticide metabolites in groundwater and surface water.
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    45. 45
      Simon, C.; Roth, V.-N.; Dittmar, T.; Gleixner, G. Molecular Signals of Heterogeneous Terrestrial Environments Identified in Dissolved Organic Matter: A Comparative Analysis of Orbitrap and Ion Cyclotron Resonance Mass Spectrometers. Frontiers in Earth Science 2018, 6, 138,  DOI: 10.3389/feart.2018.00138
      There is no corresponding record for this reference.
    46. 46
      Longnecker, K.; Oswald, L.; Soule, M. C. K.; Cutter, G. A.; Kujawinski, E. B. Organic sulfur: A spatially variable and understudied component of marine organic matter. Limnology and Oceanography Letters 2020, 5 (4), 305– 312,  DOI: 10.1002/lol2.10149
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      Organic sulfur: A spatially variable and understudied component of marine organic matter
      Longnecker, Krista; Oswald, Lisa; Kido Soule, Melissa C.; Cutter, Gregory A.; Kujawinski, Elizabeth B.
      Limnology & Oceanography Letters (2020), 5 (4), 305-312CODEN: LOLIBT; ISSN:2378-2242. (John Wiley & Sons Ltd.)
      Sulfur (S) is a major heteroatom in org. matter. This project evaluated spatial variability in the concn. and mol.-level compn. of org. sulfur along gradients of depth and latitude. We measured the concn. of total org. sulfur (TOS) directly from whole seawater. Our data reveal high variability in org. sulfur, relative to established variability in total org. carbon or nitrogen. The deep ocean contained significant amts. of org. sulfur, and the concn. of TOS in North Atlantic Deep Water (NADW) decreased with increasing age while total org. carbon remained stable. Anal. of dissolved org. matter exts. by ultrahigh resoln. mass spectrometry revealed that 6% of elemental formulas contained sulfur. The sulfur-contg. compds. were structurally diverse, and showed higher nos. of sulfur-contg. elemental formulas as NADW moved southward. These measurements of org. sulfur in seawater provide the foundation needed to define the factors controlling org. sulfur in the global ocean.
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    47. 47
      Wagner, S.; Riedel, T.; Niggemann, J.; Vahatalo, A. V.; Dittmar, T.; Jaffe, R. Linking the Molecular Signature of Heteroatomic Dissolved Organic Matter to Watershed Characteristics in World Rivers. Environ. Sci. Technol. 2015, 49 (23), 13798– 13806,  DOI: 10.1021/acs.est.5b00525
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      Linking the Molecular Signature of Heteroatomic Dissolved Organic Matter to Watershed Characteristics in World Rivers
      Wagner, Sasha; Riedel, Thomas; Niggemann, Jutta; Vahatalo, Anssi V.; Dittmar, Thorsten; Jaffe, Rudolf
      Environmental Science & Technology (2015), 49 (23), 13798-13806CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Large world rivers are significant sources of dissolved org. matter (DOM) to the oceans. Watershed geomorphol. and land use can drive the quality and reactivity of DOM. Detg. the mol. compn. of riverine DOM is essential for understanding its source, mobility and fate across landscapes. Here, DOM from the main stem of 10 global rivers covering a wide climatic range and land use features was molecularly characterized via ultrahigh-resoln. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). FT-ICR mass spectral data revealed an overall similarity in mol. components among the rivers. However, when focusing specifically on the contribution of nonoxygen heteroat. mol. formulas (CHON, CHOS, CHOP, etc.) to the bulk mol. signature, patterns relating DOM compn. and watershed land use became apparent. Greater abundances of N- and S-contg. mol. formulas were identified as unique to rivers influenced by anthropogenic inputs, whereas rivers with primarily forested watersheds had DOM signatures relatively depleted in heteroat. content. A strong correlation between cropland cover and dissolved black N was established when focusing specifically on the pyrogenic class of compds. This study demonstrated how changes in land use directly affect downstream DOM quality and could impact C and nutrient cycling on a global scale.
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    48. 48
      LaRowe, D. E.; Van Cappellen, P. Degradation of natural organic matter: A thermodynamic analysis. Geochim. Cosmochim. Acta 2011, 75 (8), 2030– 2042,  DOI: 10.1016/j.gca.2011.01.020
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      Degradation of natural organic matter: A thermodynamic analysis
      LaRowe, Douglas E.; Van Cappellen, Philippe
      Geochimica et Cosmochimica Acta (2011), 75 (8), 2030-2042CODEN: GCACAK; ISSN:0016-7037. (Elsevier B.V.)
      The oxidative degrdn. of org. matter is a key process in the biogeochem. functioning of the earth system. Quant. models of org. matter degrdn. are therefore essential for understanding the chem. state and evolution of the Earth's near-surface environment, and to forecast the biogeochem. consequences of ongoing regional and global change. The complex nature of biol. produced org. matter represents a major obstacle to the development of such models, however. The authors compare the energetics of the oxidative degrdn. of a large no. of naturally occurring org. compds. By relating the Gibbs energies of half reactions describing the complete mineralization of the compds. to their av. nominal carbon oxidn. state, it becomes possible to est. the energetic potential of the compds. based on major element (C, H, N, O, P, S) ratios. The new energetic description of org. matter can be combined with bioenergetic theory to rationalize obsd. patterns in the decompn. of natural org. matter. For example, the persistence of cell membrane derived compds. and complex orgs. in anoxic settings is consistent with their limited catabolic potential under these environmental conditions. The proposed approach opens the way to include the thermodn. properties of org. compds. in kinetic models of org. matter degrdn.
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    49. 49
      Hawkes, J. A.; D’Andrilli, J.; Agar, J. N.; Barrow, M. P.; Berg, S. M.; Catalán, N.; Chen, H.; Chu, R. K.; Cole, R. B.; Dittmar, T.; Gavard, R.; Gleixner, G.; Hatcher, P. G.; He, C.; Hess, N. J.; Hutchins, R. H. S.; Ijaz, A.; Jones, H. E.; Kew, W.; Khaksari, M.; Palacio Lozano, D. C.; Lv, J.; Mazzoleni, L. R.; Noriega Ortega, B. E.; Osterholz, H.; Radoman, N.; Remucal, C. K.; Schmitt, N. D.; Schum, S. K.; Shi, Q.; Simon, C.; Singer, G.; Sleighter, R. L.; Stubbins, A.; Thomas, M. J.; Tolic, N.; Zhang, S.; Zito, P.; Podgorski, D. C. An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry: Are we getting the same answer?. Limnol. Oceanogr.: Methods 2020, 18 (6), 235– 258,  DOI: 10.1002/lom3.10364
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      An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry: Are we getting the same answer?
      Hawkes, Jeffrey A.; D'Andrilli, Juliana; Agar, Jeffrey N.; Barrow, Mark P.; Berg, Stephanie M.; Catalan, Nuria; Chen, Hongmei; Chu, Rosalie K.; Cole, Richard B.; Dittmar, Thorsten; Gavard, Remy; Gleixner, Gerd; Hatcher, Patrick G.; He, Chen; Hess, Nancy J.; Hutchins, Ryan H. S.; Ijaz, Amna; Jones, Hugh E.; Kew, William; Khaksari, Maryam; Palacio Lozano, Diana Catalina; Lv, Jitao; Mazzoleni, Lynn R.; Noriega-Ortega, Beatriz E.; Osterholz, Helena; Radoman, Nikola; Remucal, Christina K.; Schmitt, Nicholas D.; Schum, Simeon K.; Shi, Quan; Simon, Carsten; Singer, Gabriel; Sleighter, Rachel L.; Stubbins, Aron; Thomas, Mary J.; Tolic, Nikola; Zhang, Shuzhen; Zito, Phoebe; Podgorski, David C.
      Limnology and Oceanography: Methods (2020), 18 (6), 235-258CODEN: LOMIBY; ISSN:1541-5856. (John Wiley & Sons, Inc.)
      High-resoln. mass spectrometry (HRMS) has become a vital tool for dissolved org. matter (DOM) characterization. The upward trend in HRMS anal. of DOM presents challenges in data comparison and interpretation among labs. operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with ref. samples so that data can be robustly compared among research groups. To this end, four identically prepd. DOM samples were each measured by 16 labs., using 17 com. purchased instruments, using pos.-ion and neg.-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified ∼1000 common ions in both neg.- and pos.-ion modes over a wide range of m/z values and chem. space, as detd. by van Krevelen diagrams. Calcd. metrics of abundance-weighted av. indexes (H/C, O/C, aromaticity, and m/z) of the commonly detected ions showed that hydrogen satn. and aromaticity were consistent for each ref. sample across the instruments, while av. mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
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    50. 50
      Hertkorn, N.; Frommberger, M.; Witt, M.; Koch, B. P.; Schmitt-Kopplin, P.; Perdue, E. M. Natural organic matter and the event horizon of mass spectrometry. Anal. Chem. 2008, 80 (23), 8908– 19,  DOI: 10.1021/ac800464g
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      Natural Organic Matter and the Event Horizon of Mass Spectrometry
      Hertkorn, N.; Frommberger, M.; Witt, M.; Koch, B.; Schmitt-Kopplin, Ph.; Perdue, E. M.
      Analytical Chemistry (Washington, DC, United States) (2008), 80 (23), 8908-8919CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Soils, sediments, freshwaters, and marine waters contain natural org. matter (NOM), an exceedingly complex mixt. of orgs. that collectively exhibit a nearly continuous range of properties (size-reactivity continuum). NOM is composed mainly of C, H, and O, with minor contributions from heteroatoms such as N, S, and P. Suwannee River fulvic acid (SuwFA) is a fraction of NOM that is relatively depleted in heteroatoms. Ultrahigh resoln. Fourier transform ion cyclotron (FTICR) mass spectra of SuwFA reveal several thousand mol. formulas, corresponding in turn to several hundred thousand distinct chem. environments of C even without accountancy of isomers. The mass difference Δm among adjoining C,H,O-mols. between and within clusters of nominal mass is inversely related to mol. dissimilarity: any decrease of Δm imposes an ever growing mandatory difference in mol. compn. Mol. formulas that are expected for likely biochem. precursor mols. are notably absent from these spectra, indicating that SuwFA is the product of diagenetic reactions that have altered the major components of biomass beyond the point of recognition. The degree of complexity of SuwFA can be brought into sharp focus through comparison with the theor. limits of chem. complexity, as constrained and quantized by the fundamentals of chem. binding. The theor. C,H,O-compositional space denotes the isomer-filtered complement of the entire, very vast space of mol. structures composed solely of C, H, and O. The mol. formulas within SuwFA occupy a sizable proportion of the theor. C,H,O-compositional space. A 100% coverage of the theor. feasible C,H,O-compositional space by SuwFA mols. is attained throughout a sizable range of mass and H/C and O/C elemental ratios. The substantial differences between (and complementarity of) the SuwFA mol. formulas that are obsd. using 6 different modes of ionization (APCI, APPI, and ESI in pos. and neg. modus) imply considerable selectivity of the ionization process and suggest that the obsd. mass spectra represent simplified projections of still more complex mixts.
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    51. 51
      Lechtenfeld, O. J.; Hertkorn, N.; Shen, Y.; Witt, M.; Benner, R. Marine sequestration of carbon in bacterial metabolites. Nat. Commun. 2015, 6, 6711,  DOI: 10.1038/ncomms7711
      51
      Marine sequestration of carbon in bacterial metabolites
      Lechtenfeld, Oliver J.; Hertkorn, Norbert; Shen, Yuan; Witt, Matthias; Benner, Ronald
      Nature Communications (2015), 6 (), 6711CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Linking microbial metabolomics and carbon sequestration in the ocean via refractory org. mols. has been hampered by the chem. complexity of dissolved org. matter (DOM). Here, using bioassay expts. and ultra-high resoln. metabolic profiling, we demonstrate that marine bacteria rapidly utilize simple org. mols. and produce exometabolites of remarkable mol. and structural diversity. Bacterial DOM is similar in chem. compn. and structural complexity to naturally occurring DOM in sea water. An appreciable fraction of bacterial DOM has mol. and structural properties that are consistent with those of refractory mols. in the ocean, indicating a dominant role for bacteria in shaping the refractory nature of marine DOM. The rapid prodn. of chem. complex and persistent mols. from simple biochems. demonstrates a pos. feedback between primary prodn. and refractory DOM formation. It appears that carbon sequestration in diverse and structurally complex dissolved mols. that persist in the environment is largely driven by bacteria.
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    52. 52
      Underwood, G. J. C.; Michel, C.; Meisterhans, G.; Niemi, A.; Belzile, C.; Witt, M.; Dumbrell, A. J.; Koch, B. P. Organic matter from Arctic sea-ice loss alters bacterial community structure and function. Nature Climate Change 2019, 9 (2), 170– 176,  DOI: 10.1038/s41558-018-0391-7
      There is no corresponding record for this reference.
    53. 53
      Arrieta, J. M.; Mayol, E.; Hansman, R. L.; Herndl, G. J.; Dittmar, T.; Duarte, C. M. Ocean chemistry. Dilution limits dissolved organic carbon utilization in the deep ocean. Science 2015, 348 (6232), 331– 3,  DOI: 10.1126/science.1258955
      53
      Dilution limits dissolved organic carbon utilization in the deep ocean
      Arrieta, Jesus M.; Mayol, Eva; Hansman, Roberta L.; Herndl, Gerhard J.; Dittmar, Thorsten; Duarte, Carlos M.
      Science (Washington, DC, United States) (2015), 348 (6232), 331-333CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Oceanic dissolved org. C (DOC) is the 2nd largest reservoir of org. C in the biosphere. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degrdn. An alternative hypothesis is that deep-water DOC consists of many different, intrinsically labile compds. at concns. too low to compensate for the metabolic costs assocd. to their utilization. We present exptl. evidence showing that low concns. rather than recalcitrance preclude consumption of a substantial fraction of DOC, leading to slow microbial growth in the deep ocean. These findings demonstrate an alternative mechanism for the long-term storage of labile DOC in the deep ocean, which has been hitherto largely ignored.
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    54. 54
      Shen, Y.; Benner, R. Mixing it up in the ocean carbon cycle and the removal of refractory dissolved organic carbon. Sci. Rep 2018, 8 (1), 2542,  DOI: 10.1038/s41598-018-20857-5
      54
      Mixing it up in the ocean carbon cycle and the removal of refractory dissolved organic carbon
      Shen Yuan; Benner Ronald; Shen Yuan; Benner Ronald
      Scientific reports (2018), 8 (1), 2542 ISSN:.
      A large quantity of reduced carbon is sequestered in the ocean as refractory dissolved molecules that persist through several circuits of global overturning circulation. Key aspects of the cycling of refractory dissolved organic carbon (DOC) remain unknown, making it challenging to predict how this large carbon reservoir will respond to climate change. Herein we investigate mechanisms that remove refractory DOC using bioassay experiments with DOC isolated from surface, mesopelagic and deep waters of the Atlantic Ocean. The isolated DOC was refractory to degradation by native microbial communities, even at elevated concentrations. However, when the refractory DOC was introduced to a series of novel environmental conditions, including addition of a labile substrate, a microbial community from coastal waters and exposure to solar radiation, a substantial fraction (7-13%) was removed within 1.5 years. Our results suggest that while refractory molecules can persist in the ocean for millennia, removal is rapid when they encounter their fate. The observed and projected climate-induced slowdown of global overturning circulation could reduce the exposure of refractory molecules to disparate removal processes. Assuming a constant rate of production, the reservoir size of refractory DOC could increase as overturning circulation slows, providing a negative feedback to rising atmospheric CO2.
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    55. 55
      Leefmann, T.; Frickenhaus, S.; Koch, B. P. UltraMassExplorer: a browser-based application for the evaluation of high-resolution mass spectrometric data. Rapid Commun. Mass Spectrom. 2019, 33 (2), 193– 202,  DOI: 10.1002/rcm.8315
      55
      UltraMassExplorer: a browser-based application for the evaluation of high-resolution mass spectrometric data
      Leefmann, Tim; Frickenhaus, Stephan; Koch, Boris P.
      Rapid Communications in Mass Spectrometry (2019), 33 (2), 193-202CODEN: RCMSEF; ISSN:0951-4198. (John Wiley & Sons Ltd.)
      Rationale : High-resoln. mass spectrometry (HRMS) with high sample throughput has become an important anal. tool for the anal. of highly complex samples and data processing has become a major challenge for the user community. Evaluating direct-infusion HRMS data without automated tools for batch processing can be a time-consuming step in the anal. pipeline. Therefore, we developed a new browser-based software tool for processing HRMS data. Methods : The software, named UltraMassExplorer (UME), was written in the R programming language using the shiny library to build the graphical user interface. The performance of the integrated formula library search algorithm was tested using HRMS data derived from analyses of up to 50 exts. of marine dissolved org. matter. Results : The software supports the processing of lists of calibrated masses of neutral, protonated or deprotonated mols., with masses of up to 700 Da and a mass accuracy <3 ppm. In the performance test, the no. of assigned peaks per s increased with the no. of submitted peaks and reached a max. rate of 4745 assigned peaks per s. Conclusions : UME offers a complete data evaluation pipeline comprising a fast mol. formula assignment algorithm allowing for the swift reanal. of complete datasets, advanced filter functions and the export of data, meta-data and publication-quality graphics. Unique to UME is a fast and interactive connection between data and their visual representation. UME provides a new platform enabling an increased transparency, customization, documentation and comparability of datasets.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.3c07219.

    • Additional information regarding DOC determination, instrument quality control, and method assessment, samples (Tables SI 1,2, Figure SI 1), model compounds (Tables SI 3,4, Figure SI 16), molecular descriptors and biogeochemical indices (Tables SI 5–7), LC setup (Figure SI 2), data processing (Figure SI 3), LC chromatograms (Figures SI 4–6, 12–15), chemodiversity (Figures SI 7–11), matrix effects (Figures SI 17–21), detector response (Figures SI 22–24), repeatability (Figures SI 25,26), pH effect (Figures SI 27,28), comparison with SPE extracts (Figures SI 29–34) (PDF)

    • Script for DataAnalysis (Bruker Daltonics, version 6.0) for LC-MS segmentation and spectra averaging (TXT)

    • List of surfactants (XLSX)


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    Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.