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Novel Ambient Oxidation Trends in Fingerprint Aging Discovered by Kendrick Mass Defect Analysis
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Cite this: ACS Cent. Sci. 2022, 8, 9, 1328–1335
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https://doi.org/10.1021/acscentsci.2c00408
Published September 21, 2022

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Abstract

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A Kendrick mass defect (KMD) plot is an efficient way to disperse complex high-resolution mass spectral data in a visually informative two-dimensional format which allows for the rapid assignment of compound classes that differ by heteroatom content and/or unsaturation. Fingerprint lipid oxidation has the potential to be used to estimate the time since deposition of a fingerprint, but the mass spectra become extremely complex as the lipids degrade. We apply KMD plot analysis for the first time to sebaceous fingerprints aged for 0–7 days to characterize lipid degradation processes analyzed by MALDI-MS. In addition to the ambient ozonolysis of fingerprint lipids previously reported, we observed unique spectral features associated with epoxides and medium chain fatty acid degradation products that are correlated with fingerprint age. We propose an ambient epoxidation mechanism via a peroxyl radical intermediate and the prevalence of omega-10 fatty acyl chains in fingerprint lipids to explain the features observed by the KMD plot analysis. Our hypotheses are supported by an aging experiment performed in a sparse ozone condition and on-surface Paternò–Büchi reaction. A comprehensive understanding of fingerprint degradation processes, afforded by the KMD plots, provides crucial insights for considering which ions to monitor and which to avoid, when creating a robust model for time since deposition of fingerprints.

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Synopsis

A deeper understanding of fingerprint aging is gained through the Kendrick mass defect plot-guided discovery of new mass spectral trends, providing a foundation for fingerprint age estimations.

Introduction

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Fingerprints have been a mainstay in forensic investigations since the early 1900s, due to the evidentiary value of their morphology. (1) Recently, mass spectrometry has been explored to extend the evidentiary value within a fingerprint. These efforts include but are not limited to analyzing exogenous and/or endogenous compounds within the fingerprint for suspect specific chemical information (2−7) and assessing the diffusion of compounds within fingerprints (8,9) or monitoring degradation of fingerprint compounds (10−12) for time since deposition estimations. Time since deposition, or fingerprint aging, is of special interest because such temporal evidence describes the relevance of a fingerprint to the timeline of a crime. Despite many attempts to address this gap in fingerprint forensic evidence, reliable time since deposition estimations have remained a challenge due to many reasons such as environmental considerations, fingerprint composition and formation, and surface characteristics. (13)
Recently, we proposed that the ambient ozonolysis that occurs in unsaturated triacylglycerols (TGs) of sebaceous fingerprints has the potential to be used to estimate the time since fingerprint deposition within a week. (10) The overall aging process, however, is much more complex because the ozonolysis oxidation products are intermediates and can further degrade when they contain multiple degrees of unsaturation. Additionally, other endogenous unsaturated lipids such as squalene (SQ), wax esters (WEs), fatty acids (FAs), and diacylglycerols (DGs), likely compete for the ambient ozone during degradation. (10) Consequently, though the initial composition of sebaceous fingerprints is relatively simple, comprised mostly of TGs, SQ, WEs, FAs, and DGs, the aging process produces a complex mixture of many degradation products. High-resolution mass spectrometry (HRMS) can untangle some of this complexity; however, the data analysis is still a daunting task without an efficient strategy.
Kendrick mass defect (KMD) analysis allows for the rapid grouping of congener ions into compound classes that have elemental compositions with the same heteroatom (O, N, P, S) content and unsaturation, a homologous series. The Kendrick mass (KM) was proposed in 1963 as a way to simplify spectral interpretation by normalizing the m/z values to 14 being the mass of the 12C1H2, alkyl chain unit. (14)
Compounds of similar composition, differing only in the number of CH2 units, have the same KMD, the difference between the rounded KM and KM, but differing KM. Further, compounds with the same heteroatom class can be easily identified in a two-dimensional KMD plot of the mass-to-charge ratio (m/z) vs the KMD. In the KMD plots, homologous series align horizontally, and parallel homologous series with a ΔKMD of ±0.0134 differ by a degree of unsaturation. The KMD plot has been extensively utilized in HRMS analysis of petroleum (15) but has also been extended to biofuel, (16) polymer, (17) environmental research, (18) as well as lipidomics. (19,20) In forensics, it has only been applied for synthetic designer drugs in order to streamline drug analog identification. (21)
Here we propose the use of KMD plots as a visual tool to streamline the identification of compound classes associated with fingerprint aging. Building upon our previous findings relating to ambient ozonolysis, (10) KMD analysis comprehensively reveals the molecular details of fingerprint aging processes. Our analysis led to the discovery of a new series of epoxidation products, attributed to epoxidation of carbon–carbon double bonds in TGs, WEs, FAs, and DGs by singlet oxygen. Our KMD analysis also led us to find a new aging trend associated with medium chain fatty acids (MCFA), especially FA 10:0, and other considerations for developing time since deposition models.

Results and Discussion

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Subtracted Spectra and KMD Plots for General Spectral Differences

A high-resolution Orbitrap MS connected to a MALDI source is used in this study for the analysis of aged fingerprints in ambient lab conditions. Figure 1 is the subtracted spectrum and the overlain KMD plots in the lipid KMD range (0.05–0.35) for the fresh (0-day) and 7-day aged fingerprints. To generate the subtracted spectrum, all spectral features were normalized to the summed signal of saturated TGs to account for differences in deposition. The original spectra (Figure S1), full overlain KMD plot (Figure S2), and environmental conditions during the aging (Figure S3, Table S1) can be found in the Supporting Information. KMD bubble plots are also helpful as they retain the relative abundance information of the plot features (Figure S4).

Figure 1

Figure 1. (a) Fresh fingerprint MALDI-MS spectrum subtracted from a 7-day fingerprint spectrum. (b) Zoomed-in subtracted spectrum in the y-axis. (c) Overlain KMD plot of the fresh and 7-day-old fingerprints.

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Many noticeable differences can be found in the subtracted mass spectra. Most notable is the loss of SQ (m/z 433.3805) in the aged fingerprint (Figure 1a). This is consistent with previous findings of rapid decay of SQ in aged fingerprints analyzed by GC-MS and LC-MS. (22,23) Other differences, such as the negative peaks in m/z 700–900 and positive peaks in m/z 600–800 (Figure 1b), are related to the fingerprint aging and are clearly distinguished in the KMD plot (Figure 1c). Thus, the spectral and plot differences can be used in concert in order to identify time-dependent m/z features and related series to understand the molecular details of the aging process over time. Previously, we proposed to use the degradation of TGs to monitor the time since deposition of fingerprints due to high ion abundance and multiple levels of unsaturation. (10) The ozonolysis products for TGs are readily observed as the new cluster of KMD plot features in the m/z range of ∼675–775 (blue box). However, oxidative aging of WEs, DGs, FAs, and SQ (green box) can also be studied using MALDI-HRMS with KMD analysis as described in more detail later.

Generating in Silico Theoretical Heteroatom Class List

Given the ease of visualizing the differences in plot features between the aged and fresh prints by using the subtracted spectrum and KMD plot, the subsequent task is assigning elemental compositions. Considering that TGs, WEs, DGs, FAs, and SQ can be readily detected in our MALDI condition and may undergo ambient ozonolysis, (10,24) we made an in silico theoretical target list for each elemental composition that would arise from the ozonolysis process as shown in Scheme 1. SQ was omitted from heteroatom class consideration as it is not expected to have a homologous series and is anticipated to rapidly oxidize into volatile compounds. Ambient ozone molecules react with any carbon–carbon double bonds in lipid substrates to form primary ozonides, which then rearrange to secondary ozonides. The secondary ozonide is relatively stable but breaks down slowly into the aldehyde (A) even in the ambient environment or into the aldehyde (A) and Criegee ion isomers (B or C) by in-source fragmentation during MALDI analysis.

Scheme 1

Scheme 1. Ambient Ozonolysis of Unsaturated Lipids in Fingerprints
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Most substrates in Scheme 1 can have multiple carbon-carbon double bonds which may lead to sequential ozonolysis. Therefore, a second ozonolysis process was also included for DGs, WEs, and TGs in the KM target list. The target list of heteroatom classes was created to cover the entire spectral range in order to assess any unexpected or conflicting plot features that reside in the same heteroatom class. Given that sodium acetate was used as an additive to promote cationization in positive ion mode, sodium ion adducts were the primary adducts used to produce the target list. Carboxylic acids (FA or product C in Scheme 1) are detected as disodiated, sodium adducts of sodium carboxylate, and these theoretical mass values were also included. Lastly, all classes were allowed one sodium to be replaced with potassium, in order to understand the contribution of potassium adducts to the spectral complexity; however, their contribution has a minimal impact on the interpretation based on sodium adducts. The theoretical heteroatom classes have the general form of CcH2c-ZOwNaxKy. Z-values in the formulas are related to double bond equivalents. Table S2 summarized the searched heteroatom classes, double bond equivalent (DBE) values, minimum Z-values, and their molecular constituents.

KMD Plot Annotations of Heteroatom Classes in Fingerprints

On the basis of the in silico heteroatom class list, most of the plot features in the lipid region of fresh and aged fingerprints are annotated (±2 ppm) into one of the heteroatom classes in the KMD plots (Figure S5). The mass resolving power used is sufficient to resolve Type-II isotopic overlap (Δm/z of 0.0089 between the second 13C peak and a lipid with one more saturation). (25) As we are approaching the limits of the resolving power, some 13C peaks are unresolved when the relative ion signal is very low (Figure S6). Regardless, it has minimal impact on the heteroatom class assignment based on the ±2 ppm mass tolerance.
A smaller region of the annotated KMD plot is captured in Figure 2 for the m/z of 550–1000, focusing on TGs. Substrate abbreviations followed by a letter in parentheses indicate the ozonolysis product from Scheme 1. For example, TG(A) and TG(C) indicate the A and C product of TG, respectively. TG(B/C) indicates the chemical series that are associated with the isomeric single sodiated Criegee ions, product B or C in Scheme 1. Two ozonolysis processes are also possible as observed by TG(AA), aldehyde products in two fatty acyl chains of TG, but generally have low signals. Further, in Figures 2 and S5, squares (□) represent heteroatom classes mostly dominated by unreacted lipids, while diamonds (◊) and triangles (Δ) indicate series where the predominant signals are expected to be from one or two ozonolysis processes, respectively. Potassium adducts for all heteroatom classes are also included and are denoted as black asterisks (*). The color of the symbols is chosen to make a heteroatom class stick out among its neighboring heteroatom classes. A heteroatom class is comprised of homologous series aligned horizontally at the same KMD. Parallel homologous series with a KMD difference of 0.0134 indicates a difference in unsaturation; DBEs are shown for TGs as an example in Figure 2, and saturated TGs have a DBE of 3 from three ester groups.

Figure 2

Figure 2. KMD plots for the (a) fresh and (b) 7-day-old fingerprints of the TG region with S/N > 30. Heteroatom class annotations are based solely on theoretical values in ambient ozonolysis (Scheme 1). Note the DBE of saturated TGs is three due to the three ester groups.

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Because the in silico list, based on ozonolysis products of all lipid substrates, defines most of the plot features in the aged and fresh fingerprints in Figure 2 for TG and in Figure S5 for all lipids, we are confident ambient ozonolysis plays a central role in fingerprint aging. In general, the lower mass region of the plot gets more populated (m/z < 500), consistent with oxidative degradation products. Though two sequential ozonolysis processes on the same substrate are possible for a polyunsaturated lipid, the overall contribution is minimal after 7 days. Most of the searched but absent heteroatom classes are associated with double ozonolysis products, labeled as “x” in Table S2. Investigating unannotated features is aided with using different KMD plot normalization techniques which are demonstrated and described in the Supporting Information (Supporting discussion, Figures S7–S9).

Epoxidation: A Spectral Trend Observed by 2D KMD Plots

Most of the aged products could be explained with ambient ozonolysis in Scheme 1 and are labeled as “TG(A)”, “TG(C)”, and “TG(B/C)” in Figure 2. Some aldehyde products, consistent with ozonolysis, are present even in fresh fingerprints, but they are in very low abundance and attributed to oxidation on the skin surface before the fingerprint is deposited. However, there are some trends that cannot be explained by ambient ozonolysis. Specifically, the cluster of plot features labeled as TG(E) with a solid red box cannot be explained as any of the substrates or products in Scheme 1. They have the same heteroatom class with TG(A) boxed with a dashed line, but their masses are in the range of the most abundant TGs, 770–900. This point is clearly demonstrated in the intensity profile along the same KMD. As shown in Figure 3, CcH2c-ZO7Na (DBE = 4) heteroatom class (red) has a bimodal distribution. The distribution centered at m/z ≈ 690 is TG(A) after losing an alkyl chain below the reacted double bond site from the TG ozonide. However, the distribution centered at m/z ≈ 825 has a profile similar to its potential precursor, monounsaturated TG (CcH2c-ZO7Na with DBE = 4, blue), and cannot be explained as TG(A). These features are also localized to the fingerprint, as seen in the MS images (Figure S10).

Figure 3

Figure 3. Intensity profile of CcH2c-ZO6Na (DBE = 4) and CcH2c-ZO7Na (DBE = 4) homologous series in a 7-day aged fingerprint.

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To address this trend, unexplainable by ozonolysis, we hypothesize that this series is associated with an epoxidation process induced by ambient singlet oxygen (Scheme 2). Zhou et al. proposed an ambient singlet oxygen mechanism to explain the aldehyde products in ambient surface oxidation of unsaturated lipids, (26) but it does not involve epoxidation. Weiny et al. studied the autoxidation of polyunsaturated FAs (PUFA) on monolayer thin films at 37 °C, detecting epoxide formation and confirming its structure with NMR. The mechanism proposed by Weiny et al. involves a peroxyl radical intermediate, the same as Zhou et al.’s, but the epoxides are suggested as the final products. (26,27) Therefore, singlet oxygen is a promising source for peroxyl radical intermediates in ambient conditions to explain the subsequent epoxide formation, though other autoxidation mechanisms may also lead to the peroxyl radical. There is contradictory literature evidence for the initial hydrogen abstraction. Specifically, Wu et al. suggested that minimal epoxidation occurs for lipid monolayers or bulk systems containing exclusively monounsaturated aliphatic chains under heat. (28) Thus, further investigation is necessary for the origin of peroxyl radical intermediate formation in fingerprint lipids.

Scheme 2

Scheme 2. Proposed Ambient Epoxidation Mechanism, Where the Initial Hydrogen Abstraction Is at an Allylic Carbon at R2
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SQ epoxides have also been observed in aged fingerprints, (23,29) but the epoxides of TGs, WEs, FAs, and DGs have not previously been reported in fingerprints. However, epoxides of many of these lipid species have been monitored in other systems. (27,30−32) We extend Weiny’s mechanism to include all unsaturated lipids and propose that the peroxyl radical is also generated by singlet oxygen in ambient condition as simplified in Scheme 2. This reaction scheme is consistent with the m/z values of TG(E) for having one more oxygen without alkyl chain loss from TG. The same trend is also found for other lipids as shown in Figure S5 as DG(E), WE(E), and FA(E). The epoxides are present even in the fresh sample, probably occurring on the skin surface before deposited, and carry over into the aged samples similar to TG(A). ESI-MS/MS of TG(E) from the fingerprint extracts was not successful due to poor signals, but MS/MS of FA(E) 16:0 from the same extract suggests the presence of epoxides (Figure S11). Additionally, ESI-MS/MS on the extract of aged TG standards, a mixture of TG 48:0 and TG 50:1, have fragmentation patterns consistent with epoxides (Figure S12). However, we cannot avoid the possibility that some isomeric species may also contribute to the features assigned as epoxides, such as the termination of structure D (Scheme 2) with another abstracted hydrogen to form a hydroxyl group.
To support the ambient epoxidation hypothesis, we performed an experiment in a sealed climate chamber with minimal ozone and similar or elevated levels of singlet oxygen. The relative humidity and temperature were maintained at levels similar to the ambient condition, but ozone concentration was about five times less. UVA is provided to produce singlet oxygen species from ambient oxygen; (33,34) however, the amount of singlet oxygen was not monitored. After 3 days of aging in the sparse ozone (2.7 ± 0.7 ppb) environment, the TG(E) signal is significantly greater than that of the TG(C) ozonolysis product (p < 0.001; Figure S13a), in contrast to the ambient environment where it is comparable or lower (Figure S13b). The preferential TG epoxidation, as opposed to TG ozonolysis, is consistent with our singlet oxygen hypothesis. Singlet oxygen has been suggested as an oxidant in the ambient environment (26) and has multiple routes of formation, some including origins from ozone. (35,36)
We also ruled out the possibility of other epoxide reactions. One potential explanation is peroxide containing facial cleansers, but the individual does not use such products. Additionally, TG(E) is observed in aged unsaturated TG standards as well as the fingerprints of other people. Another possibility is that epoxide formation occurs as a sample preparation artifact during the Au sputtering process (e.g., discharge excitation of oxygen impurity), but the epoxide spectral features were still present when using an organic MALDI matrix (Figure S14). Lastly, artificial epoxide formation may also happen in the laser plume plasma environment, if oxygen impurity in the MALDI source is excited by the laser. To address this possibility, nitrogen gas (99.995+%) was used to displace any oxygen that might be present in the 7.5 Torr MALDI source during analysis, but the spectral features remained the same (Figure S14).
It is important to distinguish the epoxide features from other features. For example, DG(E) has the same heteroatom class as TG and DG(A) for having O6, and TG(E) has the same heteroatom class as TG(A) for having O7, but they are differentiated by a significant mass difference. With aging, the heteroatom class broadens out significantly as low abundance lipids get oxidized, eventually overlapping, as can be seen for TG(E) and TG(A) in Figure 2b. Despite the overlap in the KMD plot, they are well separated from each other in the intensity profile as demonstrated in Figure 3 for TG(E) vs TG(A). Another example is shown in Figure S15 for DG(E), DG(A), and TG.
To evaluate the use of the epoxides for time-since-deposition estimations, the intensities of TG(E) species were monitored in fingerprints aged for different times, as summarized and grouped into the same degree of unsaturation in Figure 4. An interesting trend is observed depending on the unsaturation of the epoxides. The epoxides of monounsaturated TGs no longer have reactive double bonds (i.e., TG X:1 becomes TG(E) X:0) and appear to remain stagnant through the aging process. The stability of the homologous series suggests that the carbon–carbon double bond is likely no longer present, consistent with fully saturated epoxides instead of a hydroxyl group. In contrast, the unsaturated epoxide species decrease in intensity over time, especially those that are multiply unsaturated. As reported by Wu et al. on the autoxidation of unsaturated FAs to epoxides, we hypothesize ambient epoxidation occurs rather rapidly but almost exclusively on the top monolayer. (28) The epoxides would then stay at the same concentration if there is no additional unsaturation or degrade over time through the ozonolysis of other double bonds. Weiny et al. used the monolayers of PUFA adsorbed on silica gel particles to get a high yield of the epoxides (27), following Wu et al. (28) As ambient epoxidation occurs mostly on the top monolayers, its impact is minimal as a competing process for ozonolysis substrates and confined only to very early fingerprint aging. It is possible that multiply unsaturated epoxides might be used to model time since deposition given that they further oxidize by ozonolysis.

Figure 4

Figure 4. Monitoring TG(E) species during fingerprint aging. Epoxides are normalized to the corresponding saturated TG (e.g., TG(E)44:1/TG44:0). Error bars represent one standard deviation from four replicates.

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Medium Chain Fatty Acid Ozonolysis Product: A Spectral Trend Observed by KMD Bubble Plots

When assessing the intensity profile of the fatty acid heteroatom class (CcH2c-ZO2Na2, red □ in Figure S5), one can see a stark increase in the intensity for m/z 217.117 in the KMD bubble plots after aging for 7 days (Figure 5a). This is a peak corresponding to FA10:0, which cannot be explained as a common contamination (e.g., vacuum pump oil), and saturated lipid species should not intuitively increase in signal due to aging. Additionally, the corresponding MS image demonstrates that the ion is localized to the ridge of the fingerprint (Figure S10a). We hypothesize that this is due to the ozonolysis of fatty acyl chains with a double bond at the ω-10 position (product C in Scheme 1). If an ω-10 fatty acyl chain is common in fingerprint lipids, ozonides at the ω-10 position will accumulate over time, resulting in an abundance of FA10:0 during MALDI analysis (product C in Scheme 1).

Figure 5

Figure 5. (a) KMD bubble plot for saturated fatty acids (CcH2c-ZO2Na2, DBE = 1) in fresh and 7-day aged fingerprints. Intensity profiles for (b) saturated and (c) monounsaturated FAs during fingerprint aging. Error bars represent one standard deviation from four replicates.

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To demonstrate this possibility, an on-surface Paternò–Büchi (PB) reaction, using similar methodology from the literature, (37) was performed to determine the double bond localization for a few sampled TGs in fresh fingerprints (see Figure S16 for the workflow). In the PB reaction, the lipid double bonds react with an aldehyde or a ketone reagent under UVC to form an oxetane ring. The derivatized lipid can be selected for MS/MS to produce diagnostic fragments for the double bond position. New peaks corresponding to the PB reaction of unsaturated TGs are observed in Figure S17b, compared to no reaction (Figure S17a), which are then subjected to MS/MS. As shown in Figure S17c for the MS/MS of derivatized TG 48:2 as an example, the most abundant double bond position is ω-10 on a 16:1 acyl chain. All MS/MS results are summarized in Table S3, and ω-10 is the most abundant in all TG species investigated (56–80%). The prevalence of ω-10 is also supported by the 10-carbon difference between the peak positions of TG(A) and TG along the m/z axis, TG 47:1 vs TG(A) 37:0 (Figure 3), as well as DG(A) and DG, DG 32:1 vs DG(A) 22:0 (Figure S15). Furthermore, sapienic acid (FA16:1, ω-10), though rare generally, is known to be a unique component of sebum. (38) ESI-MS/MS of the FA(E)16:0 is consistent with the prevalence of sapienic acid in the fingerprints (Figure S11). Also, Pleik et al. reported decanal, originated from ω-10 FA, as the major fingerprint aging product in their GC-MS analysis (11) and ω-10 as a common double bond position in fingerprint TGs in their LC-MS/MS of TG ozonides. (12)
Figure 5b,c shows the intensity profiles for saturated and monounsaturated FAs during aging, respectively. One can readily see the increase of FA 10:0 over time. It appears that ω-8 through ω-11 double bond positions also have some contribution, resulting in FA 8:0 through FA 11:0, which is consistent with the PB results (Table S3). These medium chain FAs (MCFAs), especially FA 10:0, may be good candidates to monitor for aging as they increase over time. In contrast, long chain FAs, FA 13:0 through FA18:0, are consistent regardless of aging because they are not oxidation fragments but mostly endogenous fatty acids. They might be useful for normalization when FA 10:0 is used for an aging marker, to account for differences in sebum loading during deposition. However, caution is required as these FAs might also come from contaminants. For example, 10% of FA 16:0 was from contamination in our experimental condition; hence, FA 15:0 or FA 17:0, with no or minimum contamination, might be better for normalization. It contrasts with MCFAs that are rare in nature, other than coconut, palm, and milk oils; (39) thus, these features are very unlikely coming from contamination. A similar trend is found for monounsaturated FAs, especially FA 10:1 (Figure 5c), although ion intensity is much less. They are probably from polyunsaturated fingerprint lipids with an ω-10 as the second double bond position in a fatty acyl chain. The typical aging trend is found for FA 14:1 through FA 20:1, where intensity of the unsaturated signal decreases over time. It should be noted that FA 10:0 is mostly produced by in-source fragmentation of the secondary ozonide during MALDI (Scheme 1). Pleik et al. also observed FA 10:0 in their GC-MS analysis of aged fingerprints but in much lower abundance and attributed to the oxidation of decanal. (11)
A robust model for time since deposition should have multiple spectral features to describe different periods of the aging. In such a model, squalene oxidation may best describe early aging (<3 days), TG degradation captures midrange aging (2–7 days), and the accumulation of FA 10:0 has the potential to verify and extend the 7-day aging window (Figure S18). Future work will focus on kinetics-based and machine learning-based approaches to generate these models with larger data sets.

Conclusions

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Aged sebaceous fingerprints are composed of a complex lipid mixture and their oxidation products. In spite of many studies, there has been no comprehensive investigation of their degradation processes. By employing KMD plots for sebaceous fingerprint analysis, two novel discoveries were made. An oxygen atom addition to unsaturated lipids is found regardless of fingerprint lipid species. It is attributed to ambient epoxidation by singlet oxygen based on previous studies for ambient oxidation of standard lipids. It is further hypothesized that epoxidation occurs mostly on the top monolayer, which explains rapid epoxide formation but no further increase over time. Additionally, an unusual increase of FA 10:0 is found as fingerprints age, which is attributed to the Criegee ion resulting from the ozonolysis of an ω-10 fatty acyl chain. The double bond position is further verified with an on-surface Paternò–Büchi reaction, demonstrating that an ω-10 carbon–carbon double bond position is common in fingerprint TGs. The current study, using KMD plot analysis, leads to a better understanding of ambient oxidation processes in fingerprint aging and allows us to work toward developing a comprehensive model for time since deposition.

Methods

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Fingerprint Collection and Ambient Aging

Fourteen groomed fingerprints were acquired from a single individual. The individual washed their hands thoroughly with water and soap followed by air drying. The thumb was then rubbed on the donor’s forehead and a fingerprint was placed on a precleaned glass slide. Fingerprints were aged in the ambient laboratory environment for 0, 1, 3, 5, and 7 days, where 0-, 3-, and 7-day samples were analyzed in quadruplicate, and only one sample was analyzed for the 1- and 5-day samples. Relative humidity and temperature were monitored using a hygrometer (Excursion-Trac; Fisher Scientific) at 30 min intervals, and ozone was monitored using a 106-L ozone monitor (Ozone Solutions; Hull, IA, USA) at 1 min intervals. Measured values over the 7-day period are reported in Figure S3 and Table S1.

Fingerprint Sample Preparation

Fingerprints and standards were sprayed with 10 mM sodium acetate in methanol using a TM sprayer (HTX Technologies; Chapel Hill, NC, USA). A flow rate of 0.03 mL/min was used for a total of eight passes with 3 mm spacing in a crisscross pattern at a velocity of 1200 mm/min with a nitrogen gas pressure of 10 psi and nozzle temperature of 30 °C. Gold was then sputtered on top of the fingerprint for 20 s at 40 mA using a Cressington 108 auto Sputter Coater (Ted Pella; Redding, CA, USA).

Mass Spectrometry Analysis and Data Processing

A QExactive HF (Thermo Finnigan; San Jose, CA, USA) with a MALDI/ESI injector (Spectroglyph; Kennewick, WA, USA) (40) was used for positive mode MALDI-MS analysis with a mass resolution of 240,000 at m/z 200, maximum injection time of 492 ms, m/z range of 100–1200, and raster step of 50 μm. Xcalibur, an in-house Python script for the extraction of ions of interest, and MATLAB were used for data analysis.

Supporting Experiments

Methods for the experiments to produce supporting figures can be found in the Supporting Information.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscentsci.2c00408.

  • Additional experimental details and discussion, unsubtracted mass spectra, various KMD plots, summary of PB results, type-II isotopic overlap, MS images, MS/MS of epoxides and PB product, TG epoxide profiles in various conditions, separation of O6 homologous series, and promising aging features over time (PDF)

  • Data files used in the KMD plots and the PB table (ZIP)

  • Transparent Peer Review report available (PDF)

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 Author
  • Author
    • Andrew E. Paulson - Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States
  • Author Contributions

    Y.L conceived fingerprint aging with MALDI-MS and on-surface PB. A.P. conceived the application of KMD plot analysis to fingerprint aging, designed and performed experiments, and analyzed the data. The manuscript was written through contributions of all authors.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work is supported by the National Institute of Justice (2019-DU-BX-0134).

References

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This article references 40 other publications.

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    Latent fingerprints (LFPs) potentially contain more forensic information than the simple identification of the subject; they may contain evidence of contacts with explosives or substances of abuse. Chem. information could also be useful in resolving overlapping LFPs from different individuals. We used desorption electrospray ionization mass spectrometry to produce mass spectra of substances found in LFPs.
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  3. 3
    Lauzon, N.; Chaurand, P. Detection of Exogenous Substances in Latent Fingermarks by Silver-Assisted LDI Imaging MS: Perspectives in Forensic Sciences. Analyst 2018, 143 (15), 3586– 3594,  DOI: 10.1039/C8AN00688A
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    3
    Detection of exogenous substances in latent fingermarks by silver-assisted LDI imaging MS: perspectives in forensic sciences
    Lauzon, Nidia; Chaurand, Pierre
    Analyst (Cambridge, United Kingdom) (2018), 143 (15), 3586-3594CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
    For over one hundred years, the fingerprint has reigned as one of the most trusted pieces of forensic evidence for suspect identification. In the last few decades, the modernization of chem. anal. technologies led scientists to explore new possibilities to further analyze fingermarks sampled from a crime scene. Indeed, the detection of chems. a suspect has been in contact with before or during the crime can provide valuable insights into criminal investigations. In this regard, imaging mass spectrometry (IMS) has shown to be a powerful tool for the anal. of fingermarks by combining suspect identification and the detection of numerous endogenous and exogenous compds. A novel approach developed in our lab., silver-assisted laser desorption ionization (AgLDI), was adopted to allow for the chem. anal. of latent fingermarks left on nonconductive surfaces (such as paper, cardboard, plastic and forensic lifting tape) with a time-of-flight mass spectrometer. In this study, we continue to evaluate the potential of AgLDI IMS to provide circumstantial evidence by detecting exogenous substances. We first demonstrate that owner-specific chem. signatures can be recovered from fingermarks based on the presence of several cosmetics and personal care products. We then show the possibility of detecting and imaging fingermarks contg. three common illicit drugs, namely tetrahydrocannabinol, cocaine and heroin. Finally, we demonstrate that the methodol. also allows us to successfully image bloody fingermarks after appropriate forensic enhancement treatments. Overall, we believe that AgLDI IMS has significant potential that could pos. contribute to forensic investigations.
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  4. 4
    Zhou, Z.; Zare, R. N. Personal Information from Latent Fingerprints Using Desorption Electrospray Ionization Mass Spectrometry and Machine Learning. Anal. Chem. 2017, 89 (2), 1369– 1372,  DOI: 10.1021/acs.analchem.6b04498
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    4
    Personal Information from Latent Fingerprints Using Desorption Electrospray Ionization Mass Spectrometry and Machine Learning
    Zhou, Zhenpeng; Zare, Richard N.
    Analytical Chemistry (Washington, DC, United States) (2017), 89 (2), 1369-1372CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was applied to latent fingerprints to obtain not only spatial patterns but also chem. maps. Samples with similar lipid compns. as those of the fingerprints were collected by swiping a glass slide across the forehead of consenting adults. A machine learning model called gradient boosting tree ensemble (GDBT)was applied to the samples that allowed the authors to distinguish between different genders, ethnicities, and ages (within ten years). The results from 194 samples showed accuracies of 89.2%, 82.4%, and 84.3% resp. Specific chem. species that were detd. by the feature selection of GDBT were identified by tandem mass spectrometry. As a proof-of-concept, the machine learning model trained on the sample data was applied to overlaid latent fingerprints from different individuals, giving accurate gender and ethnicity information from those fingerprints. The results suggest that DESI-MSI imaging of fingerprints with GDBT anal. might offer a significant advance in forensic science.
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  5. 5
    Hinners, P.; O’Neill, K. C.; Lee, Y. J. Revealing Individual Lifestyles through Mass Spectrometry Imaging of Chemical Compounds in Fingerprints. Sci. Rep 2018, 8 (1), 5149,  DOI: 10.1038/s41598-018-23544-7
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    5
    Revealing Individual Lifestyles through Mass Spectrometry Imaging of Chemical Compounds in Fingerprints
    Hinners Paige; O'Neill Kelly C; Lee Young Jin
    Scientific reports (2018), 8 (1), 5149 ISSN:.
    Fingerprints, specifically the ridge details within the print, have long been used in forensic investigations for individual identification. Beyond the ridge detail, fingerprints contain useful chemical information. The study of fingerprint chemical information has become of interest, especially with mass spectrometry imaging technologies. Mass spectrometry imaging visualizes the spatial relationship of each compound detected, allowing ridge detail and chemical information in a single analysis. In this work, a range of exogenous fingerprint compounds that may reveal a personal lifestyle were studied using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Studied chemical compounds include various brands of bug sprays and sunscreens, as well as food oils, alcohols, and citrus fruits. Brand differentiation and source determination were possible based on the active ingredients or exclusive compounds left in fingerprints. Tandem mass spectrometry was performed for the key compounds, so that these compounds could be confidently identified in a single multiplex mass spectrometry imaging data acquisition.
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  6. 6
    O’Neill, K. C.; Hinners, P.; Lee, Y. J. Potential of Triacylglycerol Profiles in Latent Fingerprints to Reveal Individual Diet, Exercise, or Health Information for Forensic Evidence. Anal. Methods 2020, 12 (6), 792– 798,  DOI: 10.1039/C9AY02652E
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    6
    Potential of triacylglycerol profiles in latent fingerprints to reveal individual diet, exercise, or health information for forensic evidence
    O'Neill, Kelly C.; Hinners, Paige; Lee, Young Jin
    Analytical Methods (2020), 12 (6), 792-798CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
    Triacylglycerols (TGs) are a primary component of human skin oils and are therefore a major constituent present in latent fingerprint residue. We hypothesize that differences in the TG profile of the latent fingerprint, such as the relative level of satn. of the fatty acyl chains, may link back to the overall health of the subject, specifically correlated to diabetes. A small scale proof-of-concept study was performed to test this hypothesis. The biggest differences obsd. were in the relative amts. of completely satd. TGs compared to TGs with one or more double bonds; however, hierarchical clustering could not differentiate diabetic and non-diabetic participants. The role of other factors such as diet and exercise was explored from subsets of the non-diabetic participants. Vegetarian participants had higher relative levels of satd. TGs compared to those without diet restrictions; however, people on a low carbohydrate or ketogenic diet were not distinguishable from the control population. In terms of exercise, male participants who were very active had lower levels of satd. TGs compared to males who did not exercise at all. In contrast, exercise did not have much of an effect on the TG profile of female participants. While the outcome of this study is only tentative due to the lack of statistical power, it suggests the potential of TG profiles to be linked to health information, diet and exercise.
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  7. 7
    Bradshaw, R.; Denison, N.; Francese, S. Implementation of MALDI MS Profiling and Imaging Methods for the Analysis of Real Crime Scene Fingermarks. Analyst 2017, 142 (9), 1581– 1590,  DOI: 10.1039/C7AN00218A
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    7
    Implementation of MALDI MS profiling and imaging methods for the analysis of real crime scene fingermarks
    Bradshaw, R.; Denison, N.; Francese, S.
    Analyst (Cambridge, United Kingdom) (2017), 142 (9), 1581-1590CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
    In the study presented here, four examples of crime scene fingermarks analyzed by Matrix Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI MSI), in collaboration with the local Police Force, are reported. These marks are assocd. to high profile crimes such as drug dealing, murder and harassment. Following the application of forensic enhancement techniques by the CSI or the crime lab, one of the marks could be directly analyzed on the surface of deposition and the others were analyzed as primary lifts. In one case, no phys. or mol. information was obtained, whereas in two cases both ridge detail (albeit not useful for identification purposes) and mol. information could be retrieved. In one case, the intelligence gathered around the suspect's state of mind is, to date the most accomplished demonstration of the benefits and the operational feasibility MALDI MS based methods. These four casework examples are to be considered a first insight into the limitations, benefits and feasibility of MALDI MS based methods in the field; due to the extreme variability in the state of the mark, comprehensive evaluation of these aspects can only be undertaken upon the anal. of a large no. of crime scene marks. However, this work does represent a significant advancement, compared to previous published work, as it demonstrates operational feasibility, with different levels of success, despite uncontrollable, unknown and unaccountable environmental and donor variability.
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  8. 8
    Muramoto, S.; Sisco, E. Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analyzed Using Time-of-Flight Secondary Ion Mass Spectrometry. Anal. Chem. 2015, 87 (16), 8035– 8038,  DOI: 10.1021/acs.analchem.5b02018
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    8
    Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analyzed Using Time-of-Flight Secondary Ion Mass Spectrometry
    Muramoto, Shin; Sisco, Edward P.
    Analytical Chemistry (Washington, DC, United States) (2015), 87 (16), 8035-8038CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Age dating of fingerprints could have a significant impact in forensic science, as it has the potential to facilitate the judicial process by assessing the relevance of a fingerprint found at a crime scene. However, no method currently exists that can reliably predict the age of a latent fingerprint. In this manuscript, time-of-flight secondary ion imaging mass spectrometry (TOF-SIMS) was used to measure the diffusivity of satd. fatty acid mols. from a fingerprint on a silicon wafer. It was found that their diffusion from relatively fresh fingerprints (t ≤96 h) could be modeled using an error function, with diffusivities (Mm2/h) that followed a power function when plotted against mol. wt. The equation x = 0.02t0.5 was obtained for palmitic acid that could be used to find its position in millimeters (where the concn. is 50% of its initial value or c0/2) as a function of time in hours. The results show that on a clean silicon substrate, the age of a fingerprint (t ≤96 h) could reliably be obtained through the extent of diffusion of palmitic acid.
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  9. 9
    O’Neill, K. C.; Lee, Y. J. Effect of Aging and Surface Interactions on the Diffusion of Endogenous Compounds in Latent Fingerprints Studied by Mass Spectrometry Imaging. J. Forensic Sci. 2018, 63 (3), 708– 713,  DOI: 10.1111/1556-4029.13591
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    9
    Effect of Aging and Surface Interactions on the Diffusion of Endogenous Compounds in Latent Fingerprints Studied by Mass Spectrometry Imaging,
    O'Neill, Kelly C.; Lee, Young Jin
    Journal of Forensic Sciences (2018), 63 (3), 708-713CODEN: JFSCAS; ISSN:0022-1198. (John Wiley & Sons, Inc.)
    The ability to det. the age of fingerprints would be immeasurably beneficial in criminal investigations. We explore the possibility of detg. the age of fingerprints by analyzing various compds. as they diffuse from the ridges to the valleys of fingerprints using matrix-assisted laser desorption/ionization mass spectrometry imaging. The diffusion of two classes of endogenous fingerprint compds., fatty acids and triacylglycerols (TGs), was studied in fresh and aged fingerprints on four surfaces. We expected higher mol. wt. TGs would diffuse slower than fatty acids and allow us to det. the age of older fingerprints. However, we found interactions between endogenous compds. and the surface have a much stronger impact on diffusion than mol. wt. For example, diffusion of TGs is faster on hydrophilic plain glass or partially hydrophilic stainless steel surfaces, than on a hydrophobic Rain-x treated surface. This result further complicates utilizing a diffusion model to age fingerprints.
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  10. 10
    Hinners, P.; Thomas, M.; Lee, Y. J. Determining Fingerprint Age with Mass Spectrometry Imaging via Ozonolysis of Triacylglycerols. Anal. Chem. 2020, 92 (4), 3125– 3132,  DOI: 10.1021/acs.analchem.9b04765
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    10
    Determining Fingerprint Age with Mass Spectrometry Imaging via Ozonolysis of Triacylglycerols
    Hinners, Paige; Thomas, Madison; Lee, Young Jin
    Analytical Chemistry (Washington, DC, United States) (2020), 92 (4), 3125-3132CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Despite the common use of fingerprints as a trusted means of identification, no method currently exists to reliably establish the time since deposition of latent fingerprints. A reproducible method of establishing latent fingerprint age would allow forensic personnel to det. if a latent fingerprint was relevant to a crime. This work investigates the ambient aging of triacylglycerols (TGs) and other lipids in latent fingerprint residue utilizing matrix-assisted laser desorption/ionization mass spectrometry imaging. Unsatd. TGs were found to undergo ambient ozonolysis resulting in a decrease over time. At the same time, two series of compds. related to the degrdn. of unsatd. TGs due to ambient ozonolysis emerged with time and were detectable within a single day of aging. Tracking the degrdn. of unsatd. TGs over time proved to be relatively reproducible in multiple individuals and is suggested as a means of establishing latent fingerprint age.
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  11. 11
    Pleik, S.; Spengler, B.; Schäfer, T.; Urbach, D.; Luhn, S.; Kirsch, D. Fatty Acid Structure and Degradation Analysis in Fingerprint Residues. J. Am. Soc. Mass Spectrom. 2016, 27 (9), 1565– 1574,  DOI: 10.1007/s13361-016-1429-6
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    11
    Fatty Acid Structure and Degradation Analysis in Fingerprint Residues
    Pleik, Stefanie; Spengler, Bernhard; Schaefer, Thomas; Urbach, Dieter; Luhn, Steven; Kirsch, Dieter
    Journal of the American Society for Mass Spectrometry (2016), 27 (9), 1565-1574CODEN: JAMSEF; ISSN:1044-0305. (Springer)
    GC-MS investigations were carried out to elucidate the aging behavior of unsatd. fatty acids in fingerprint residues and to identify their degrdn. products in aged samples. For this purpose, a new sample prepn. technique for fingerprint residues was developed that allows producing N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA) derivs. of the analyzed unsatd. fatty acids and their degrdn. products. MSTFA derivatization catalyzed by iodotrimethylsilane enables the reliable identification of aldehydes and oxoacids as characteristic MSTFA derivs. in GCMS. The obtained results elucidate the degrdn. pathway of unsatd. fatty acids. Our study of aged fingerprint residues reveals that decanal is the main degrdn. product of the obsd. unsatd. fatty acids. Furthermore, oxoacids with different chain lengths are detected as specific degrdn. products of the unsatd. fatty acids. The detection of the degrdn. products and their chain length is a simple and effective method to det. the double bond position in unsatd. compds. We can show that the hexadecenoic and octadecenoic acids found in fingerprint residues are not the pervasive fatty acids Δ9-hexadecenoic (palmitoleic acid) and Δ9-octadecenoic (oleic acid) acid but Δ6-hexadecenoic acid (sapienic acid) and Δ8-octadecenoic acid. The present study focuses on the structure identification of human sebum-specific unsatd. fatty acids in fingerprint residues based on the identification of their degrdn. products. These results are discussed for further investigations and method developments for age detn. of fingerprints, which is still a tremendous challenge because of several factors affecting the aging behavior of individual compds. in fingerprints.
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  12. 12
    Pleik, S.; Spengler, B.; Ram Bhandari, D.; Luhn, S.; Schäfer, T.; Urbach, D.; Kirsch, D. Ambient-Air Ozonolysis of Triglycerides in Aged Fingerprint Residues. Analyst 2018, 143 (5), 1197– 1209,  DOI: 10.1039/C7AN01506B
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    12
    Ambient-air ozonolysis of triglycerides in aged fingerprint residues
    Pleik, Stefanie; Spengler, Bernhard; Ram Bhandari, Dhaka; Luhn, Steven; Schaefer, Thomas; Urbach, Dieter; Kirsch, Dieter
    Analyst (Cambridge, United Kingdom) (2018), 143 (5), 1197-1209CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
    In forensic science, reconstructing the timing of events occurring during a criminal offense is of great importance. In some cases, the time when particular evidence was left on a crime scene is a crit. matter. The ability to est. the fingerprint age would raise the evidentiary value of fingerprints tremendously. For this purpose the most promising approach is the anal. of changes in the chem. compns. of fingerprint residues in the course of aging. The focus of our study is the identification of human specific compds. in fingerprint residues, characterized by a significant aging behavior that could anal. be used for the age detn. of fingerprints in future. The first challenge is the sensitive detection of trace amts. of relevant human specific fingerprint compds. Highly sensitive LC-MS methods were developed for the reliable structure identification of unsatd. triglycerides and their natural degrdn. products in order to proof the aging mechanism that takes place in fingerprint residues. Thus our results build the fundamental basis for further forensic method development and potential application in forensic investigation. Ozonolysis was found to be one of the major lipid degrdn. pathways in fingerprint residues in ambient air. High-resoln. tandem mass spectrometry (HRMS2) was carried out to identify the ozonolysis products (TG48:0-monoozonide) formed under exposure to the highly reactive ozone in atm. air. The obtained products were confirmed by matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). Despite several challenges and limitations in the age estn. of fingerprints, the identification of individual degrdn. products of specific unsatd. lipids in aged fingerprint samples represents a significant anal. progress, resulting in a strong increase in the validity of chem. anal. of fingerprints.
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  13. 13
    Frick, A. A.; Girod-Frais, A.; Moraleda, A.; Weyermann, C. Latent Fingermark Aging: Chemical Degradation Over Time. In Technologies for Fingermark Age Estimations: A Step Forward; De Alcaraz-Fossoul, J., Ed.; Springer International Publishing: Cham, 2021; pp 205– 235,  DOI: 10.1007/978-3-030-69337-4_7 .
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    Kendrick, E. A Mass Scale Based on CH2 = 14.0000 for High Resolution Mass Spectrometry of Organic Compounds. Anal. Chem. 1963, 35 (13), 2146– 2154,  DOI: 10.1021/ac60206a048
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    Mass scale based on CH2 = 14.0000 for high-resolution mass spectrometry of organic compounds
    Kendrick, Edward
    (1963), 35 (13), 2146-54CODEN: ANCHAM; ISSN:0003-2700.
    The advantages of this scale are: (1) ions differing by one or more CH2 groups have the same mass defect; (2) the no. of precise masses to be calcd., stored, and compared with data from a sample is reduced; (3) the same defects apply in the higher mass ranges; (4) the identification of ions is simplified. Tables are presented of the mass defects for combinations of H, 12C, 13C, N, O, 32S, and 34S.
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    Marshall, A. G.; Rodgers, R. P. Petroleomics: The Next Grand Challenge for Chemical Analysis. Acc. Chem. Res. 2004, 37 (1), 53– 59,  DOI: 10.1021/ar020177t
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    Petroleomics: The Next Grand Challenge for Chemical Analysis
    Marshall, Alan G.; Rodgers, Ryan P.
    Accounts of Chemical Research (2004), 37 (1), 53-59CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Ultrahigh-resoln. Fourier transform ion cyclotron resonance mass spectrometry has recently revealed that petroleum crude oil contains heteroatom-contg. (N,O,S) org. components having more than 20,000 distinct elemental compns. (CcHhNnOoSs). It is therefore now possible to contemplate the ultimate characterization of all of the chem. constituents of petroleum, along with their interactions and reactivity, a concept we denote as "petroleomics". Such knowledge has already proved capable of distinguishing petroleum and its distillates according to their geochem. origin and maturity, distn. cut, extn. method, catalytic processing, etc. The key features that have opened up this new field have been (a) ultrahigh-resoln. FT-ICR mass anal., specifically, the capability to resolve species differing in elemental compn. by C3 vs SH4 (i.e., 0.0034 Da); (b) higher magnetic field to cover the whole mass range at once; (c) dynamic range extension by external mass filtering; and (d) plots of Kendrick mass defect vs nominal Kendrick mass as a means for sorting different compd. "classes" (i.e., nos. of N, O, and S atoms), "types" (rings plus double bonds), and alkylation ((-CH2)n) distributions, thereby extending to >900 Da the upper limit for unique assignment of elemental compn. based on accurate mass measurement. The same methods are also being applied successfully to anal. of humic and fulvic acids, coals, and other complex natural mixts., often without prior or online chromatog. sepn.
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    Smith, E. A.; Lee, Y. J. Petroleomic Analysis of Bio-Oils from the Fast Pyrolysis of Biomass: Laser Desorption Ionization–Linear Ion Trap–Orbitrap Mass Spectrometry Approach. Energy Fuels 2010, 24 (9), 5190– 5198,  DOI: 10.1021/ef100629a
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    16
    Petroleomic Analysis of Bio-oils from the Fast Pyrolysis of Biomass: Laser Desorption Ionization-Linear Ion Trap-Orbitrap Mass Spectrometry Approach
    Smith, Erica A.; Lee, Young Jin
    Energy & Fuels (2010), 24 (9), 5190-5198CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
    Fast pyrolysis of biomass produces bio-oils that can be upgraded into biofuels. Despite similar phys. properties to petroleum, the chem. properties of bio-oils are quite different and their chem. compns., particularly those of non-volatile compds., are not well-known. Here, we report the first time attempt at analyzing bio-oils using high-resoln. mass spectrometry (MS), which employed laser desorption ionization-linear ion trap-Orbitrap MS. Besides a few limitations, we could det. chem. compns. for over 100 mol. compds. in a bio-oil sample produced from the pyrolysis of a loblolly pine tree. These compds. consist of 3-6 oxygens and 9-17 double-bond equiv. (DBEs). Among those, O4 compds. with a DBE of 9-13 were most abundant. Unlike petroleum oils, the lack of nearby mols. within a ±2 Da mass window for major components enabled clear isolation of precursor ions for subsequent MS/MS structural investigations. Petroleomic anal. and a comparison to low-mass components in hydrolytic lignin suggest that they are dimers and trimers of depolymd. lignin.
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    Fouquet, T. N. J. The Kendrick Analysis for Polymer Mass Spectrometry. J. Mass Spectrom 2019, 54 (12), 933– 947,  DOI: 10.1002/jms.4480
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    The Kendrick analysis for polymer mass spectrometry
    Fouquet, Thierry N. J.
    Journal of Mass Spectrometry (2019), 54 (12), 933-947CODEN: JMSPFJ; ISSN:1076-5174. (John Wiley & Sons Ltd.)
    A review. The mass spectrum of a polymer often displays repetitive patterns with peak series spaced by the repeating unit(s) of the polymeric backbones, sometimes complexified with different adducts, chain terminations, or charge states. Exploring the complex mass spectral data or filtering the unwanted signal is tedious whether performed manually or automatically. In contrast, the now 60-yr-old Kendrick (mass defect) anal., when adapted to polymer ions, produces visual two-dimensional maps with intuitive alignments of the repetitive patterns and favorable deconvolution of features overlaid in the one-dimensional mass spectrum. This special feature article reports on an up-to-date and theor. sound use of Kendrick plots as a data processing tool. The approach requires no prior knowledge of the sample but offers promising dynamic capabilities for visualizing, filtering, and sometimes assigning congested mass spectra. Examples of applications of the approach to polymers are discussed throughout the text, but the same tools can be readily extended to other applications, including the anal. of polymers present as pollutants/contaminants, and to other analytes incorporating a repetitive moiety, for example, oils or lipids. In each of these instances, data processing can benefit from the application of an updated and interactive Kendrick anal.
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    Smith, J. S.; Laskin, A.; Laskin, J. Molecular Characterization of Biomass Burning Aerosols Using High-Resolution Mass Spectrometry. Anal. Chem. 2009, 81 (4), 1512– 1521,  DOI: 10.1021/ac8020664
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    Molecular Characterization of Biomass Burning Aerosols Using High-Resolution Mass Spectrometry
    Smith, Jeffrey S.; Laskin, Alexander; Laskin, Julia
    Analytical Chemistry (Washington, DC, United States) (2009), 81 (4), 1512-1521CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Chem. characterization of atm. aerosols presents a serious anal. challenge due to the complexity of particulate matter analytes composed of a large no. of compds. with a range of mol. structures, physicochem. properties, and reactivity. The chem. compn. of org. constituents of biomass burning aerosol (BBA) was characterized by high-resoln. electro-spray ionization mass spectrometry (ESI/MS). Accurate mass measurement combined with Kendrick anal. assigned an elemental compn. for hundreds of compds. in the 50-1000 m/z value range. ESI/MS spectra of different BBA samples contain a variety of distinct, sample-specific, characteristic peaks which can be used as unique markers for different types of biofuels. Results indicated a significant no. of high mol. wt. org. compds. in BBA samples were highly oxidized polar species which can be efficiently detected by ESI/MS but which are difficult to observe using conventional gas-chromatog./mass spectrometry aerosol sample anal. More than 70% of identified species have not been reported in the literature. Detected org. compds. exhibited a clear increase in the degree of satn., since the mol. wt. of analyte mols. increased. This increase was particularly pronounced for samples contg. a large no. of the CH2-based homologous series.
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    Lerno, L. A.; German, J. B.; Lebrilla, C. B. Method for the Identification of Lipid Classes Based on Referenced Kendrick Mass Analysis. Anal. Chem. 2010, 82 (10), 4236– 4245,  DOI: 10.1021/ac100556g
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    19
    Method for the Identification of Lipid Classes Based on Referenced Kendrick Mass Analysis
    Lerno, Larry A., Jr.; German, J. Bruce; Lebrilla, Carlito B.
    Analytical Chemistry (Washington, DC, United States) (2010), 82 (10), 4236-4245CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    A rapid method for the detn. of lipid classes with high sensitivity is described. The referenced Kendrick mass defect (RKMD) and RKMD plots are novel adaptations of the Kendrick mass defect anal. that allows for the rapid identification of members of a homologous series in addn. to identifying the lipid class. Assignment of lipid classes by the RKMD method is accomplished by conversion of the lipid masses to the Kendrick mass scale and then referencing the converted masses to each lipid class. Referencing of the masses to a given lipid class is achieved by first subtracting the heteroatom and lipid backbone contributions to the mass defect, leaving behind the contribution to the mass by the fatty acid constituents. The final step in the referencing makes use of spacing differences in mass defects between members of the same Kendrick class to identify members of the lipid class being referenced. The end result of this is that a lipid belonging to the class being referenced will have an integer RKMD with the value of the integer being the degrees of unsatn. in the lipid. The RKMD method was able to successfully identify the lipids in an idealized data set consisting of 160 lipids drawn from the glyceride and phosphoglyceride classes. As a real world example the lipid ext. from bovine milk was analyzed using both accurate mass measurements and the RKMD method.
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  20. 20
    Kune, C.; McCann, A.; Raphaël, L. R.; Arias, A. A.; Tiquet, M.; Van Kruining, D.; Martinez, P. M.; Ongena, M.; Eppe, G.; Quinton, L.; Far, J.; De Pauw, E. Rapid Visualization of Chemically Related Compounds Using Kendrick Mass Defect As a Filter in Mass Spectrometry Imaging. Anal. Chem. 2019, 91 (20), 13112– 13118,  DOI: 10.1021/acs.analchem.9b03333
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    20
    Rapid Visualization of Chemically Related Compounds Using Kendrick Mass Defect As a Filter in Mass Spectrometry Imaging
    Kune, Christopher; McCann, Andrea; Raphael, La Rocca; Arias, Anthony Arguelles; Tiquet, Mathieu; Van Kruining, Daan; Martinez, Pilar Martinez; Ongena, Marc; Eppe, Gauthier; Quinton, Loic; Far, Johann; De Pauw, Edwin
    Analytical Chemistry (Washington, DC, United States) (2019), 91 (20), 13112-13118CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Kendrick mass defect (KMD) anal. is widely used for helping the detection and identification of chem. related compds. based on exact mass measurements. We report here the use of KMD as a criterion for filtering complex mass spectrometry data set. The method allow automated, easy and efficient data processing, enabling the reconstruction of 2D distributions of families of homologous compds. from MSI images. We show that KMD filtering, based on inhouse software, is suitable and robust for high resoln. (full width at half-max., fwhm, at m/z 410 of 20 000) and very high-resoln. (fwhm, at m/z 410 of 160 000) MSI data. This method has been successfully applied to two different types of samples, bacteria cocultures, and brain tissue sections.
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  21. 21
    Anstett, A.; Chu, F.; Alonso, D. E.; Smith, R. W. Characterization of 2C-Phenethylamines Using High-Resolution Mass Spectrometry and Kendrick Mass Defect Filters. Forensic Chemistry 2018, 7, 47– 55,  DOI: 10.1016/j.forc.2017.12.006
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    21
    Characterization of 2C-phenethylamines using high-resolution mass spectrometry and Kendrick mass defect filters
    Anstett, Alexandria; Chu, Fanny; Alonso, David E.; Smith, Ruth Waddell
    Forensic Chemistry (2018), 7 (), 47-55CODEN: FCOHAQ; ISSN:2468-1709. (Elsevier B.V.)
    The identification of synthetic designer drugs is challenging due to the high degree of structural similarity among compds. within a given class. In efforts to circumvent current legislation, new designer drug analogs that appear on the market have the same core structure as a regulated compd. but differ only in the position or the identity of a single substituent. Ref. stds. of the new analogs are not immediately available for comparison, making identification using conventional gas chromatog.-mass spectrometry (GC-MS) methods more challenging. In this work, the potential of mass defect to characterize compds. according to structural subclass was investigated. This initial work focused on synthetic phenethylamines, with the development of mass defect filters to characterize compds. as 2,5-dimethoxy-phenethylamines (2C-phenethylamines). Three sets of phenethylamines, including 2C-, aminopropylbenzofuran (APB-), and 2,5-dimethoxy-N-(2-methoxybenzyl) (NBOMe-) phenethylamines, were analyzed by GC-time-of-flight mass spectrometry (GC-TOFMS), using different instruments and under different conditions. The resulting accurate mass data were used to develop Kendrick mass defect filters based on the mol. ion and common neutral losses obsd. in a training set of 2C-phenethylamines. Successful characterization of test set compds. as 2C-phenethylamines with distinction from other structurally similar phenethylamines was demonstrated using the mol. ion and neutral loss mass defect filters.
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  22. 22
    Archer, N. E.; Charles, Y.; Elliott, J. A.; Jickells, S. Changes in the Lipid Composition of Latent Fingerprint Residue with Time after Deposition on a Surface. Forensic Science International 2005, 154 (2–3), 224– 239,  DOI: 10.1016/j.forsciint.2004.09.120
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    22
    Changes in the lipid composition of latent fingerprint residue with time after deposition on a surface
    Archer, Nia E.; Charles, Yannis; Elliott, Julia A.; Jickells, Sue
    Forensic Science International (2005), 154 (2-3), 224-239CODEN: FSINDR; ISSN:0379-0738. (Elsevier Ltd.)
    The work described in this report was focused on generating increased knowledge of fingerprint chem., particularly the compn. of a latent fingerprint at the time it is deposited, and the chem. changes in lipid components that occur over time. Fingerprints from 5 male donors (aged 25-34 years) were collected and aged under controlled conditions. The prints were then sampled at set intervals, solvent extd. with dichloromethane, co-derivatized with MSTFA and analyzed by gas chromatog.-mass spectrometry (GC-MS). It was shown that there was loss of squalene from prints stored in the light or in the dark. Loss was more rapid in the light, with squalene in prints from some donors not detected after 9 days storage. For these same donors, squalene was still detected after 33 days storage in the dark, but at much lower levels than in fresh prints. For satd. fatty acids (tetradecanoic, palmitic and stearic acid) there was a trend towards an increase in levels of these substances during storage (up to about 20 days) followed by a decrease back to original levels or below. This was the case for samples stored in the light or in the dark. For palmitoleic acid, a similar trend was seen. For oleic acid, this trend was seen for samples stored in the dark. For samples stored in the light the general trend was a decrease in level over the storage period (up to 33 days).
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  23. 23
    Dorakumbura, B. N.; Busetti, F.; Lewis, S. W. Analysis of Squalene and Its Transformation By-Products in Latent Fingermarks by Ultrahigh-Performance Liquid Chromatography-High Resolution Accurate Mass OrbitrapTM Mass Spectrometry. Forensic Chemistry 2020, 17, 100193,  DOI: 10.1016/j.forc.2019.100193
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    23
    Analysis of squalene and its transformation by-products in latent fingermarks by ultrahigh-performance liquid chromatography-high resolution accurate mass Orbitrap mass spectrometry
    Dorakumbura, Buddhika N.; Busetti, Francesco; Lewis, Simon W.
    Forensic Chemistry (2020), 17 (), 100193CODEN: FCOHAQ; ISSN:2468-1709. (Elsevier B.V.)
    Transformation of squalene and its byproducts in latent fingermarks over time under different storage conditions (light, dark, and underwater) was examd. through ultrahigh-performance liq. chromatog.-high resoln. accurate mass Orbitrap mass spectrometry. Complications of assessing fingermark compositional variation over time using multiple samples with varying initial compns. were elucidated and a more rational approach was successfully demonstrated. Squalene was detected in all fresh natural fingermarks deposited on non-porous surfaces and the amt. ranged between 0.20 and 11.32μg/5 fingertips. A notable difference in the transformation of squalene was obsd. with different storage conditions, where a dark aquatic environment accelerated degrdn. of squalene compared to dark but dry conditions. Squalene monohydroperoxide was extremely short-lived in natural deposits while the amt. of squalene epoxide was still increasing relative to the initial amt., after ageing under dark and aquatic conditions for up to 7 days. Some oxidn. byproducts of cholesterol were also tentatively identified, which exhibited a growth over time against their initial concn. under any of the storage condition tested. These byproducts, therefore, show potential as biomarkers for targeted visualisation of aged deposits.
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    Poad, B. L. J.; Pham, H. T.; Thomas, M. C.; Nealon, J. R.; Campbell, J. L.; Mitchell, T. W.; Blanksby, S. J. Ozone-Induced Dissociation on a Modified Tandem Linear Ion-Trap: Observations of Different Reactivity for Isomeric Lipids. J. Am. Soc. Mass Spectrom. 2010, 21 (12), 1989– 1999,  DOI: 10.1016/j.jasms.2010.08.011
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    Ozone-Induced Dissociation on a Modified Tandem Linear Ion-Trap: Observations of Different Reactivity for Isomeric Lipids
    Poad, Berwyck L. J.; Pham, Huong T.; Thomas, Michael C.; Nealon, Jessica R.; Campbell, J. Larry; Mitchell, Todd W.; Blanksby, Stephen J.
    Journal of the American Society for Mass Spectrometry (2010), 21 (12), 1989-1999CODEN: JAMSEF; ISSN:1044-0305. (Elsevier B.V.)
    Ozone-induced dissocn. (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to det. the position(s) of unsatn. In this contribution, the authors describe the modification of a tandem linear ion-trap mass spectrometer specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides spatial sepn. between mass-selection, the ozonolysis reaction, and mass-anal. steps in the OzID process and thus delivers significant enhancements in speed and sensitivity (∼30-fold). These improvements allow spectra revealing the double-bond position(s) within unsatd. lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput lipidomic protocols. The stable ozone concn. afforded by this modified instrument also allows direct comparison of relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution position on the glycerol backbone, and (3) stereochem. For cis- and trans-isomers, differences were also obsd. in the branching ratio of product ions arising from the gas-phase ozonolysis reaction, suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Addnl. activation energy applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra contg. both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsatd. phosphatidylcholine within a cow brain lipid ext. provided evidence for up to four structurally distinct phospholipids differing in both double-bond position and sn-substitution.
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    Höring, M.; Ejsing, C. S.; Krautbauer, S.; Ertl, V. M.; Burkhardt, R.; Liebisch, G. Accurate Quantification of Lipid Species Affected by Isobaric Overlap in Fourier-Transform Mass Spectrometry. J. Lipid Res. 2021, 62, 100050,  DOI: 10.1016/j.jlr.2021.100050
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    25
    Accurate quantification of lipid species affected by isobaric overlap in Fourier-transform mass spectrometry
    Horing Marcus; Krautbauer Sabrina; Ertl Verena M; Burkhardt Ralph; Ejsing Christer S; Liebisch Gerhard
    Journal of lipid research (2021), 62 (), 100050 ISSN:.
    Lipidomics data require consideration of ions with near-identical masses, which comprises among others the Type-II isotopic overlap. This overlap occurs in series of lipid species differing only by number of double bonds (DBs) mainly because of the natural abundance of (13)C-atoms. High-resolution mass spectrometry, such as Fourier-transform mass spectrometry (FTMS), is capable of resolving Type-II overlap depending on mass resolving power. In this work, we evaluated FTMS quantification accuracy of lipid species affected by Type-II overlap. Spike experiments with lipid species pairs of various lipid classes were analyzed by flow injection analysis-FTMS. Accuracy of quantification was evaluated without and with Type-II correction (using relative isotope abundance) as well as utilizing the first isotopic peak (M+1). Isobaric peaks, which were sufficiently resolved, were most accurate without Type-II correction. In cases of partially resolved peaks, we observed peak interference causing distortions in mass and intensity, which is a well-described phenomenon in FTMS. Concentrations of respective species were more accurate when calculated from M+1. Moreover, some minor species, affected by considerable Type-II overlap, could only be quantified by M+1. Unexpectedly, even completely unresolved peaks were substantially overcorrected by Type-II correction because of peak interference. The described method was validated including intraday and interday precisions for human serum and fibroblast samples. Taken together, our results show that accurate quantification of lipid species by FTMS requires resolution-depended data analysis.
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    Zhou, Y.; Park, H.; Kim, P.; Jiang, Y.; Costello, C. E. Surface Oxidation under Ambient Air─Not Only a Fast and Economical Method to Identify Double Bond Positions in Unsaturated Lipids But Also a Reminder of Proper Lipid Processing. Anal. Chem. 2014, 86 (12), 5697– 5705,  DOI: 10.1021/ac404214a
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    Surface Oxidation under Ambient Air - Not Only a Fast and Economical Method to Identify Double Bond Positions in Unsaturated Lipids But Also a Reminder of Proper Lipid Processing
    Zhou, Ying; Park, Hyejung; Kim, Philseok; Jiang, Yan; Costello, Catherine E.
    Analytical Chemistry (Washington, DC, United States) (2014), 86 (12), 5697-5705CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    A simple, fast approach elucidated carbon-carbon double bond positions in unsatd. lipids. Lipids were deposited onto various surfaces and the products from their oxidn. in ambient air were obsd. by electrospray ionization (ESI) mass spectrometry (MS). The most common oxidative products, aldehydes, were detected as transformations at the cleaved double bond positions. Ozonides and carboxylic acids were generated in certain lipids. Studies of the conditions controlling the appearance of these products indicated that the surface oxidn. depends on light and ambient air. Since the lipid oxidn. was slower in a high concn. of ozone, singlet oxygen appeared to be a parallel oxidant for unsatd. lipids. The 3-hydroxyl group in the sphingoid base of sulfatides offered some protection from oxidn. for the Δ4,5-double bond, slowing its oxidn. rate relative to that of the isolated double bond in the N-linked fatty acyl chain. Direct sampling by thin-layer chromatog. (TLC)-ESI-MS provides a powerful approach to elucidate detailed structural information on biol. samples. Co-localization of the starting lipids and their oxidn. products after TLC sepn. allowed assignment of the native unsatn. sites. Phosphatidylserine and N,N-di-Me phosphatidylethanolamine isomers in a bovine brain total lipid ext. were distinguished on the basis of their oxidn. products. Meanwhile, the findings reported herein reveal a potential pitfall in the assignment of structures to lipids extd. from TLC plates because of artifactual oxidn. after the plate development.
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    Weiny, J. A.; Boeglin, W. E.; Calcutt, M. W.; Stec, D. F.; Brash, A. R. Monolayer Autoxidation of Arachidonic Acid to Epoxyeicosatrienoic Acids as a Model of Their Potential Formation in Cell Membranes. J. Lipid Res. 2022, 63 (1), 100159,  DOI: 10.1016/j.jlr.2021.100159
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    27
    Monolayer autoxidation of arachidonic acid to epoxyeicosatrienoic acids as a model of their potential formation in cell membranes
    Weiny, James A.; Boeglin, William E.; Calcutt, M. Wade; Stec, Donald F.; Brash, Alan R.
    Journal of Lipid Research (2022), 63 (1), 100159CODEN: JLPRAW; ISSN:1539-7262. (Elsevier Inc.)
    In light of the importance of epoxyeicosatrienoic acids (EETs) in mammalian pathophysiol., a nonenzymic route that might form these monoepoxides in cells is of significant interest. In the late 1970s, a simple system of arranging linoleic acid mols. on a monolayer on silica was devised and shown to yield monoepoxides as the main autoxidn. products. Here, we investigated this system with arachidonic acid and characterized the primary products. By the early stages of autoxidn. (∼10% conversion of arachidonic acid), the major products detected by LC-MS and HPLC-UV were the 14,15-, 11,12-, and 8,9-EETs, with the 5,6-EET mainly represented as the 5-δ-lactone-6-hydroxyeicosatrienoate as established by 1H-NMR. The EETs were mainly the cis epoxides as expected, with minor trans configuration EETs among the products. 1H-NMR anal. in four deuterated solvents helped clarify the epoxide configurations. EET formation in monolayers involves intermol. reaction with a fatty acid peroxyl radical, producing the EET and leaving an incipient and more reactive alkoxyl radical, which in turn gives rise to epoxy-hydro(pero)xides and other polar products. The monolayer alignment of fatty acid mols. resembles the arrangements of fatty acids in cell membranes and, under conditions of lipid peroxidn., this intermol. mechanism might contribute to EET formation in biol. membranes.
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    Wu, G.-S.; Stein, R. A.; Mead, J. F. Autoxidation of Fatty Acid Monolayers Adsorbed on Silica Gel: II. Rates and Products. Lipids 1977, 12 (11), 971– 978,  DOI: 10.1007/BF02533320
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    Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products
    Wu, Guey-Shuang; Stein, Robert A.; Mead, James F.
    Lipids (1977), 12 (11), 971-8CODEN: LPDSAP; ISSN:0024-4201.
    Unsatd. fatty acid monolayers on silica gel were autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies were studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60°. The rates of autoxidn. of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates were considerably faster than that in bulk phase. The rates conformed to apparent 1st-order kinetics. Autoxidn. of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amt. of diene conjugation. The major products formed were 9,10-epoxy- and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidn. was stereospecific, with cis- and trans-olefins giving cis- and trans-epoxides, resp. Oleic acid was autoxidized to only a small extent during 27 h and produced no detectable amt. of epoxide.
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    Mountfort, K. A.; Bronstein, H.; Archer, N.; Jickells, S. M. Identification of Oxidation Products of Squalene in Solution and in Latent Fingerprints by ESI-MS and LC/APCI-MS. Anal. Chem. 2007, 79 (7), 2650– 2657,  DOI: 10.1021/ac0623944
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    29
    Identification of Oxidation Products of Squalene in Solution and in Latent Fingerprints by ESI-MS and LC/APCI-MS
    Mountfort, Katrina A.; Bronstein, Hugo; Archer, Nia; Jickells, Sue M.
    Analytical Chemistry (Washington, DC, United States) (2007), 79 (7), 2650-2657CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    An investigation was carried out to identify oxidn. products of squalene (SQ) in latent fingerprints. Oxidn. products of SQ incubated in soln. with Rose Bengal as a photooxidizer were isolated by semipreparative HPLC-UV and identified by direct infusion ESI-MS and flow injection APCI-MS. Squalene hydroperoxides ranging from squalene monohydroperoxide (SQ-[OOH]) to SQ-[OOH]5 were identified together with SQ epoxide. SQ-[OOH] was the main oxidn. product. An LC/APCI-MS method was developed and used to monitor the fate of SQ in soln. and in latent fingerprints and the formation of SQ-[OOH] and SQ epoxide. SQ-[OOH] and SQ epoxide were detected in freshly deposited prints but increased markedly after 1 day and continued to increase up to 5 days after print deposition. By day 7, these substances could no longer be detected in prints. SQ was rapidly depleted from prints such that by day 7 it was no longer detected. A similar pattern was seen for SQ stored in the light in dichloromethane but with a slower formation of SQ-[OOH] and SQ epoxide. The oxidn. of SQ in soln. in the presence and absence of photooxidizer was shown by TLC to proceed as follows: SQ → SQ-[OOH] + SQ epoxide. SQ-[OOH] → SQ-[OOH]2 → SQ-[OOH]3 → SQ-[OOH]4 + SQ-[OOH]5, with oxidn. being more rapid in the presence of photooxidizer. SQ-[OOH]4 and SQ-[OOH]5 could still be detected at 20 days in a soln. of SQ aged in soln. in the absence of photooxidizer. The oxidn. products of SQ should make suitable targets for development of new reagents for visualizing latent fingerprints in forensic science.
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    Grüneis, V.; Fruehwirth, S.; Zehl, M.; Ortner, J.; Schamann, A.; König, J.; Pignitter, M. Simultaneous Analysis of Epoxidized and Hydroperoxidized Triacylglycerols in Canola Oil and Margarine by LC-MS. J. Agric. Food Chem. 2019, 67 (36), 10174– 10184,  DOI: 10.1021/acs.jafc.9b03601
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    Simultaneous Analysis of Epoxidized and Hydroperoxidized Triacylglycerols in Canola Oil and Margarine by LC-MS
    Grueneis, Verena; Fruehwirth, Sarah; Zehl, Martin; Ortner, Johanna; Schamann, Alexandra; Koenig, Juergen; Pignitter, Marc
    Journal of Agricultural and Food Chemistry (2019), 67 (36), 10174-10184CODEN: JAFCAU; ISSN:0021-8561. (American Chemical Society)
    The progress of lipid oxidn. in foods is evaluated by measuring the peroxides and their scission products. However, hydrogen abstraction-independent pathways are not considered by commonly applied methods despite the known reactivity of epoxides towards biomols. Herein, a novel LC-MS/MS method was developed to detect hydroperoxidized and epoxidized triacylglycerols (TAGs) without derivatization or hydrolyzation of food samples. Epoxidized TAGs could be detected in refined canola oil at concns. of 96.8±2.08μM, while only 5.77±0.04μM hydroperoxidized TAGs could be detd. In contrast to canola oil, margarine was more resistant to lipid oxidn. since generation of epoxidized TAGs could only be marginally enhanced from 21.7±0.48μM to 28.8±0.64μM in margarine after treatment at 180°C for 60 min, as also reflected by a peroxide value of 0.80±0.00 meq O2/kg, which remained unchanged. The new method allows the assessment of food safety by the simultaneous measurement of hydroperoxidized and epoxidized TAGs without hydrolysis and laborious sample prepn.
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    Sevanian, A.; Mead, J. F.; Stein, R. A. Epoxides as Products of Lipid Autoxidation in Rat Lungs. Lipids 1979, 14 (7), 634– 643,  DOI: 10.1007/BF02533449
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    Epoxides as products of lipid autoxidation in rat lungs
    Sevanian, Alex; Mead, James F.; Stein, Robert A.
    Lipids (1979), 14 (7), 634-43CODEN: LPDSAP; ISSN:0024-4201.
    The nature and content of lipid epoxides in rat lung were examd. in air-breathing control rats and in those exposed to NO2. Exposure to 6.5 ppm NO2 for 24 h resulted in significantly greater epoxide content in a no. of lipid classes. Apparently, exposure to oxidizing gases can lead to an accumulation of lipid epoxides in both lung parenchymal tissue and on the alveolar surface.
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    Butovich, I. A.; Wojtowicz, J. C.; Molai, M. Human Tear Film and Meibum. Very Long Chain Wax Esters and (O-Acyl)-Omega-Hydroxy Fatty Acids of Meibum. J. Lipid Res. 2009, 50 (12), 2471– 2485,  DOI: 10.1194/jlr.M900252-JLR200
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  1. Kim Frisch, Kirstine L. Nielsen, Jo̷rgen B. Hasselstro̷m, Rikke Fink, Stine V. Rasmussen, Mogens Johannsen. Desorption Electrospray Ionization Mass Spectrometry Imaging of Powder-Treated Fingermarks on Forensic Gelatin Lifters and its Application for Separating Overlapping Fingermarks. Analytical Chemistry 2024, 96 (30) , 12497-12507. https://doi.org/10.1021/acs.analchem.4c02305
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  • Abstract

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    Figure 1

    Figure 1. (a) Fresh fingerprint MALDI-MS spectrum subtracted from a 7-day fingerprint spectrum. (b) Zoomed-in subtracted spectrum in the y-axis. (c) Overlain KMD plot of the fresh and 7-day-old fingerprints.

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    Scheme 1

    Scheme 1. Ambient Ozonolysis of Unsaturated Lipids in Fingerprints
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    Figure 2

    Figure 2. KMD plots for the (a) fresh and (b) 7-day-old fingerprints of the TG region with S/N > 30. Heteroatom class annotations are based solely on theoretical values in ambient ozonolysis (Scheme 1). Note the DBE of saturated TGs is three due to the three ester groups.

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    Figure 3

    Figure 3. Intensity profile of CcH2c-ZO6Na (DBE = 4) and CcH2c-ZO7Na (DBE = 4) homologous series in a 7-day aged fingerprint.

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    Scheme 2

    Scheme 2. Proposed Ambient Epoxidation Mechanism, Where the Initial Hydrogen Abstraction Is at an Allylic Carbon at R2
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    Figure 4

    Figure 4. Monitoring TG(E) species during fingerprint aging. Epoxides are normalized to the corresponding saturated TG (e.g., TG(E)44:1/TG44:0). Error bars represent one standard deviation from four replicates.

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    Figure 5

    Figure 5. (a) KMD bubble plot for saturated fatty acids (CcH2c-ZO2Na2, DBE = 1) in fresh and 7-day aged fingerprints. Intensity profiles for (b) saturated and (c) monounsaturated FAs during fingerprint aging. Error bars represent one standard deviation from four replicates.

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  • References

    This article references 40 other publications.

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      Latent fingerprints (LFPs) potentially contain more forensic information than the simple identification of the subject; they may contain evidence of contacts with explosives or substances of abuse. Chem. information could also be useful in resolving overlapping LFPs from different individuals. We used desorption electrospray ionization mass spectrometry to produce mass spectra of substances found in LFPs.
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      For over one hundred years, the fingerprint has reigned as one of the most trusted pieces of forensic evidence for suspect identification. In the last few decades, the modernization of chem. anal. technologies led scientists to explore new possibilities to further analyze fingermarks sampled from a crime scene. Indeed, the detection of chems. a suspect has been in contact with before or during the crime can provide valuable insights into criminal investigations. In this regard, imaging mass spectrometry (IMS) has shown to be a powerful tool for the anal. of fingermarks by combining suspect identification and the detection of numerous endogenous and exogenous compds. A novel approach developed in our lab., silver-assisted laser desorption ionization (AgLDI), was adopted to allow for the chem. anal. of latent fingermarks left on nonconductive surfaces (such as paper, cardboard, plastic and forensic lifting tape) with a time-of-flight mass spectrometer. In this study, we continue to evaluate the potential of AgLDI IMS to provide circumstantial evidence by detecting exogenous substances. We first demonstrate that owner-specific chem. signatures can be recovered from fingermarks based on the presence of several cosmetics and personal care products. We then show the possibility of detecting and imaging fingermarks contg. three common illicit drugs, namely tetrahydrocannabinol, cocaine and heroin. Finally, we demonstrate that the methodol. also allows us to successfully image bloody fingermarks after appropriate forensic enhancement treatments. Overall, we believe that AgLDI IMS has significant potential that could pos. contribute to forensic investigations.
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      Personal Information from Latent Fingerprints Using Desorption Electrospray Ionization Mass Spectrometry and Machine Learning
      Zhou, Zhenpeng; Zare, Richard N.
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      Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was applied to latent fingerprints to obtain not only spatial patterns but also chem. maps. Samples with similar lipid compns. as those of the fingerprints were collected by swiping a glass slide across the forehead of consenting adults. A machine learning model called gradient boosting tree ensemble (GDBT)was applied to the samples that allowed the authors to distinguish between different genders, ethnicities, and ages (within ten years). The results from 194 samples showed accuracies of 89.2%, 82.4%, and 84.3% resp. Specific chem. species that were detd. by the feature selection of GDBT were identified by tandem mass spectrometry. As a proof-of-concept, the machine learning model trained on the sample data was applied to overlaid latent fingerprints from different individuals, giving accurate gender and ethnicity information from those fingerprints. The results suggest that DESI-MSI imaging of fingerprints with GDBT anal. might offer a significant advance in forensic science.
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      Hinners, P.; O’Neill, K. C.; Lee, Y. J. Revealing Individual Lifestyles through Mass Spectrometry Imaging of Chemical Compounds in Fingerprints. Sci. Rep 2018, 8 (1), 5149,  DOI: 10.1038/s41598-018-23544-7
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      Revealing Individual Lifestyles through Mass Spectrometry Imaging of Chemical Compounds in Fingerprints
      Hinners Paige; O'Neill Kelly C; Lee Young Jin
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      Fingerprints, specifically the ridge details within the print, have long been used in forensic investigations for individual identification. Beyond the ridge detail, fingerprints contain useful chemical information. The study of fingerprint chemical information has become of interest, especially with mass spectrometry imaging technologies. Mass spectrometry imaging visualizes the spatial relationship of each compound detected, allowing ridge detail and chemical information in a single analysis. In this work, a range of exogenous fingerprint compounds that may reveal a personal lifestyle were studied using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Studied chemical compounds include various brands of bug sprays and sunscreens, as well as food oils, alcohols, and citrus fruits. Brand differentiation and source determination were possible based on the active ingredients or exclusive compounds left in fingerprints. Tandem mass spectrometry was performed for the key compounds, so that these compounds could be confidently identified in a single multiplex mass spectrometry imaging data acquisition.
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      Potential of triacylglycerol profiles in latent fingerprints to reveal individual diet, exercise, or health information for forensic evidence
      O'Neill, Kelly C.; Hinners, Paige; Lee, Young Jin
      Analytical Methods (2020), 12 (6), 792-798CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
      Triacylglycerols (TGs) are a primary component of human skin oils and are therefore a major constituent present in latent fingerprint residue. We hypothesize that differences in the TG profile of the latent fingerprint, such as the relative level of satn. of the fatty acyl chains, may link back to the overall health of the subject, specifically correlated to diabetes. A small scale proof-of-concept study was performed to test this hypothesis. The biggest differences obsd. were in the relative amts. of completely satd. TGs compared to TGs with one or more double bonds; however, hierarchical clustering could not differentiate diabetic and non-diabetic participants. The role of other factors such as diet and exercise was explored from subsets of the non-diabetic participants. Vegetarian participants had higher relative levels of satd. TGs compared to those without diet restrictions; however, people on a low carbohydrate or ketogenic diet were not distinguishable from the control population. In terms of exercise, male participants who were very active had lower levels of satd. TGs compared to males who did not exercise at all. In contrast, exercise did not have much of an effect on the TG profile of female participants. While the outcome of this study is only tentative due to the lack of statistical power, it suggests the potential of TG profiles to be linked to health information, diet and exercise.
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    7. 7
      Bradshaw, R.; Denison, N.; Francese, S. Implementation of MALDI MS Profiling and Imaging Methods for the Analysis of Real Crime Scene Fingermarks. Analyst 2017, 142 (9), 1581– 1590,  DOI: 10.1039/C7AN00218A
      7
      Implementation of MALDI MS profiling and imaging methods for the analysis of real crime scene fingermarks
      Bradshaw, R.; Denison, N.; Francese, S.
      Analyst (Cambridge, United Kingdom) (2017), 142 (9), 1581-1590CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
      In the study presented here, four examples of crime scene fingermarks analyzed by Matrix Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI MSI), in collaboration with the local Police Force, are reported. These marks are assocd. to high profile crimes such as drug dealing, murder and harassment. Following the application of forensic enhancement techniques by the CSI or the crime lab, one of the marks could be directly analyzed on the surface of deposition and the others were analyzed as primary lifts. In one case, no phys. or mol. information was obtained, whereas in two cases both ridge detail (albeit not useful for identification purposes) and mol. information could be retrieved. In one case, the intelligence gathered around the suspect's state of mind is, to date the most accomplished demonstration of the benefits and the operational feasibility MALDI MS based methods. These four casework examples are to be considered a first insight into the limitations, benefits and feasibility of MALDI MS based methods in the field; due to the extreme variability in the state of the mark, comprehensive evaluation of these aspects can only be undertaken upon the anal. of a large no. of crime scene marks. However, this work does represent a significant advancement, compared to previous published work, as it demonstrates operational feasibility, with different levels of success, despite uncontrollable, unknown and unaccountable environmental and donor variability.
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    8. 8
      Muramoto, S.; Sisco, E. Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analyzed Using Time-of-Flight Secondary Ion Mass Spectrometry. Anal. Chem. 2015, 87 (16), 8035– 8038,  DOI: 10.1021/acs.analchem.5b02018
      8
      Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analyzed Using Time-of-Flight Secondary Ion Mass Spectrometry
      Muramoto, Shin; Sisco, Edward P.
      Analytical Chemistry (Washington, DC, United States) (2015), 87 (16), 8035-8038CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Age dating of fingerprints could have a significant impact in forensic science, as it has the potential to facilitate the judicial process by assessing the relevance of a fingerprint found at a crime scene. However, no method currently exists that can reliably predict the age of a latent fingerprint. In this manuscript, time-of-flight secondary ion imaging mass spectrometry (TOF-SIMS) was used to measure the diffusivity of satd. fatty acid mols. from a fingerprint on a silicon wafer. It was found that their diffusion from relatively fresh fingerprints (t ≤96 h) could be modeled using an error function, with diffusivities (Mm2/h) that followed a power function when plotted against mol. wt. The equation x = 0.02t0.5 was obtained for palmitic acid that could be used to find its position in millimeters (where the concn. is 50% of its initial value or c0/2) as a function of time in hours. The results show that on a clean silicon substrate, the age of a fingerprint (t ≤96 h) could reliably be obtained through the extent of diffusion of palmitic acid.
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    9. 9
      O’Neill, K. C.; Lee, Y. J. Effect of Aging and Surface Interactions on the Diffusion of Endogenous Compounds in Latent Fingerprints Studied by Mass Spectrometry Imaging. J. Forensic Sci. 2018, 63 (3), 708– 713,  DOI: 10.1111/1556-4029.13591
      9
      Effect of Aging and Surface Interactions on the Diffusion of Endogenous Compounds in Latent Fingerprints Studied by Mass Spectrometry Imaging,
      O'Neill, Kelly C.; Lee, Young Jin
      Journal of Forensic Sciences (2018), 63 (3), 708-713CODEN: JFSCAS; ISSN:0022-1198. (John Wiley & Sons, Inc.)
      The ability to det. the age of fingerprints would be immeasurably beneficial in criminal investigations. We explore the possibility of detg. the age of fingerprints by analyzing various compds. as they diffuse from the ridges to the valleys of fingerprints using matrix-assisted laser desorption/ionization mass spectrometry imaging. The diffusion of two classes of endogenous fingerprint compds., fatty acids and triacylglycerols (TGs), was studied in fresh and aged fingerprints on four surfaces. We expected higher mol. wt. TGs would diffuse slower than fatty acids and allow us to det. the age of older fingerprints. However, we found interactions between endogenous compds. and the surface have a much stronger impact on diffusion than mol. wt. For example, diffusion of TGs is faster on hydrophilic plain glass or partially hydrophilic stainless steel surfaces, than on a hydrophobic Rain-x treated surface. This result further complicates utilizing a diffusion model to age fingerprints.
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    10. 10
      Hinners, P.; Thomas, M.; Lee, Y. J. Determining Fingerprint Age with Mass Spectrometry Imaging via Ozonolysis of Triacylglycerols. Anal. Chem. 2020, 92 (4), 3125– 3132,  DOI: 10.1021/acs.analchem.9b04765
      10
      Determining Fingerprint Age with Mass Spectrometry Imaging via Ozonolysis of Triacylglycerols
      Hinners, Paige; Thomas, Madison; Lee, Young Jin
      Analytical Chemistry (Washington, DC, United States) (2020), 92 (4), 3125-3132CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Despite the common use of fingerprints as a trusted means of identification, no method currently exists to reliably establish the time since deposition of latent fingerprints. A reproducible method of establishing latent fingerprint age would allow forensic personnel to det. if a latent fingerprint was relevant to a crime. This work investigates the ambient aging of triacylglycerols (TGs) and other lipids in latent fingerprint residue utilizing matrix-assisted laser desorption/ionization mass spectrometry imaging. Unsatd. TGs were found to undergo ambient ozonolysis resulting in a decrease over time. At the same time, two series of compds. related to the degrdn. of unsatd. TGs due to ambient ozonolysis emerged with time and were detectable within a single day of aging. Tracking the degrdn. of unsatd. TGs over time proved to be relatively reproducible in multiple individuals and is suggested as a means of establishing latent fingerprint age.
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    11. 11
      Pleik, S.; Spengler, B.; Schäfer, T.; Urbach, D.; Luhn, S.; Kirsch, D. Fatty Acid Structure and Degradation Analysis in Fingerprint Residues. J. Am. Soc. Mass Spectrom. 2016, 27 (9), 1565– 1574,  DOI: 10.1007/s13361-016-1429-6
      11
      Fatty Acid Structure and Degradation Analysis in Fingerprint Residues
      Pleik, Stefanie; Spengler, Bernhard; Schaefer, Thomas; Urbach, Dieter; Luhn, Steven; Kirsch, Dieter
      Journal of the American Society for Mass Spectrometry (2016), 27 (9), 1565-1574CODEN: JAMSEF; ISSN:1044-0305. (Springer)
      GC-MS investigations were carried out to elucidate the aging behavior of unsatd. fatty acids in fingerprint residues and to identify their degrdn. products in aged samples. For this purpose, a new sample prepn. technique for fingerprint residues was developed that allows producing N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA) derivs. of the analyzed unsatd. fatty acids and their degrdn. products. MSTFA derivatization catalyzed by iodotrimethylsilane enables the reliable identification of aldehydes and oxoacids as characteristic MSTFA derivs. in GCMS. The obtained results elucidate the degrdn. pathway of unsatd. fatty acids. Our study of aged fingerprint residues reveals that decanal is the main degrdn. product of the obsd. unsatd. fatty acids. Furthermore, oxoacids with different chain lengths are detected as specific degrdn. products of the unsatd. fatty acids. The detection of the degrdn. products and their chain length is a simple and effective method to det. the double bond position in unsatd. compds. We can show that the hexadecenoic and octadecenoic acids found in fingerprint residues are not the pervasive fatty acids Δ9-hexadecenoic (palmitoleic acid) and Δ9-octadecenoic (oleic acid) acid but Δ6-hexadecenoic acid (sapienic acid) and Δ8-octadecenoic acid. The present study focuses on the structure identification of human sebum-specific unsatd. fatty acids in fingerprint residues based on the identification of their degrdn. products. These results are discussed for further investigations and method developments for age detn. of fingerprints, which is still a tremendous challenge because of several factors affecting the aging behavior of individual compds. in fingerprints.
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    12. 12
      Pleik, S.; Spengler, B.; Ram Bhandari, D.; Luhn, S.; Schäfer, T.; Urbach, D.; Kirsch, D. Ambient-Air Ozonolysis of Triglycerides in Aged Fingerprint Residues. Analyst 2018, 143 (5), 1197– 1209,  DOI: 10.1039/C7AN01506B
      12
      Ambient-air ozonolysis of triglycerides in aged fingerprint residues
      Pleik, Stefanie; Spengler, Bernhard; Ram Bhandari, Dhaka; Luhn, Steven; Schaefer, Thomas; Urbach, Dieter; Kirsch, Dieter
      Analyst (Cambridge, United Kingdom) (2018), 143 (5), 1197-1209CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
      In forensic science, reconstructing the timing of events occurring during a criminal offense is of great importance. In some cases, the time when particular evidence was left on a crime scene is a crit. matter. The ability to est. the fingerprint age would raise the evidentiary value of fingerprints tremendously. For this purpose the most promising approach is the anal. of changes in the chem. compns. of fingerprint residues in the course of aging. The focus of our study is the identification of human specific compds. in fingerprint residues, characterized by a significant aging behavior that could anal. be used for the age detn. of fingerprints in future. The first challenge is the sensitive detection of trace amts. of relevant human specific fingerprint compds. Highly sensitive LC-MS methods were developed for the reliable structure identification of unsatd. triglycerides and their natural degrdn. products in order to proof the aging mechanism that takes place in fingerprint residues. Thus our results build the fundamental basis for further forensic method development and potential application in forensic investigation. Ozonolysis was found to be one of the major lipid degrdn. pathways in fingerprint residues in ambient air. High-resoln. tandem mass spectrometry (HRMS2) was carried out to identify the ozonolysis products (TG48:0-monoozonide) formed under exposure to the highly reactive ozone in atm. air. The obtained products were confirmed by matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). Despite several challenges and limitations in the age estn. of fingerprints, the identification of individual degrdn. products of specific unsatd. lipids in aged fingerprint samples represents a significant anal. progress, resulting in a strong increase in the validity of chem. anal. of fingerprints.
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    13. 13
      Frick, A. A.; Girod-Frais, A.; Moraleda, A.; Weyermann, C. Latent Fingermark Aging: Chemical Degradation Over Time. In Technologies for Fingermark Age Estimations: A Step Forward; De Alcaraz-Fossoul, J., Ed.; Springer International Publishing: Cham, 2021; pp 205– 235,  DOI: 10.1007/978-3-030-69337-4_7 .
      There is no corresponding record for this reference.
    14. 14
      Kendrick, E. A Mass Scale Based on CH2 = 14.0000 for High Resolution Mass Spectrometry of Organic Compounds. Anal. Chem. 1963, 35 (13), 2146– 2154,  DOI: 10.1021/ac60206a048
      14
      Mass scale based on CH2 = 14.0000 for high-resolution mass spectrometry of organic compounds
      Kendrick, Edward
      (1963), 35 (13), 2146-54CODEN: ANCHAM; ISSN:0003-2700.
      The advantages of this scale are: (1) ions differing by one or more CH2 groups have the same mass defect; (2) the no. of precise masses to be calcd., stored, and compared with data from a sample is reduced; (3) the same defects apply in the higher mass ranges; (4) the identification of ions is simplified. Tables are presented of the mass defects for combinations of H, 12C, 13C, N, O, 32S, and 34S.
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    15. 15
      Marshall, A. G.; Rodgers, R. P. Petroleomics: The Next Grand Challenge for Chemical Analysis. Acc. Chem. Res. 2004, 37 (1), 53– 59,  DOI: 10.1021/ar020177t
      15
      Petroleomics: The Next Grand Challenge for Chemical Analysis
      Marshall, Alan G.; Rodgers, Ryan P.
      Accounts of Chemical Research (2004), 37 (1), 53-59CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Ultrahigh-resoln. Fourier transform ion cyclotron resonance mass spectrometry has recently revealed that petroleum crude oil contains heteroatom-contg. (N,O,S) org. components having more than 20,000 distinct elemental compns. (CcHhNnOoSs). It is therefore now possible to contemplate the ultimate characterization of all of the chem. constituents of petroleum, along with their interactions and reactivity, a concept we denote as "petroleomics". Such knowledge has already proved capable of distinguishing petroleum and its distillates according to their geochem. origin and maturity, distn. cut, extn. method, catalytic processing, etc. The key features that have opened up this new field have been (a) ultrahigh-resoln. FT-ICR mass anal., specifically, the capability to resolve species differing in elemental compn. by C3 vs SH4 (i.e., 0.0034 Da); (b) higher magnetic field to cover the whole mass range at once; (c) dynamic range extension by external mass filtering; and (d) plots of Kendrick mass defect vs nominal Kendrick mass as a means for sorting different compd. "classes" (i.e., nos. of N, O, and S atoms), "types" (rings plus double bonds), and alkylation ((-CH2)n) distributions, thereby extending to >900 Da the upper limit for unique assignment of elemental compn. based on accurate mass measurement. The same methods are also being applied successfully to anal. of humic and fulvic acids, coals, and other complex natural mixts., often without prior or online chromatog. sepn.
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    16. 16
      Smith, E. A.; Lee, Y. J. Petroleomic Analysis of Bio-Oils from the Fast Pyrolysis of Biomass: Laser Desorption Ionization–Linear Ion Trap–Orbitrap Mass Spectrometry Approach. Energy Fuels 2010, 24 (9), 5190– 5198,  DOI: 10.1021/ef100629a
      16
      Petroleomic Analysis of Bio-oils from the Fast Pyrolysis of Biomass: Laser Desorption Ionization-Linear Ion Trap-Orbitrap Mass Spectrometry Approach
      Smith, Erica A.; Lee, Young Jin
      Energy & Fuels (2010), 24 (9), 5190-5198CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
      Fast pyrolysis of biomass produces bio-oils that can be upgraded into biofuels. Despite similar phys. properties to petroleum, the chem. properties of bio-oils are quite different and their chem. compns., particularly those of non-volatile compds., are not well-known. Here, we report the first time attempt at analyzing bio-oils using high-resoln. mass spectrometry (MS), which employed laser desorption ionization-linear ion trap-Orbitrap MS. Besides a few limitations, we could det. chem. compns. for over 100 mol. compds. in a bio-oil sample produced from the pyrolysis of a loblolly pine tree. These compds. consist of 3-6 oxygens and 9-17 double-bond equiv. (DBEs). Among those, O4 compds. with a DBE of 9-13 were most abundant. Unlike petroleum oils, the lack of nearby mols. within a ±2 Da mass window for major components enabled clear isolation of precursor ions for subsequent MS/MS structural investigations. Petroleomic anal. and a comparison to low-mass components in hydrolytic lignin suggest that they are dimers and trimers of depolymd. lignin.
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    17. 17
      Fouquet, T. N. J. The Kendrick Analysis for Polymer Mass Spectrometry. J. Mass Spectrom 2019, 54 (12), 933– 947,  DOI: 10.1002/jms.4480
      17
      The Kendrick analysis for polymer mass spectrometry
      Fouquet, Thierry N. J.
      Journal of Mass Spectrometry (2019), 54 (12), 933-947CODEN: JMSPFJ; ISSN:1076-5174. (John Wiley & Sons Ltd.)
      A review. The mass spectrum of a polymer often displays repetitive patterns with peak series spaced by the repeating unit(s) of the polymeric backbones, sometimes complexified with different adducts, chain terminations, or charge states. Exploring the complex mass spectral data or filtering the unwanted signal is tedious whether performed manually or automatically. In contrast, the now 60-yr-old Kendrick (mass defect) anal., when adapted to polymer ions, produces visual two-dimensional maps with intuitive alignments of the repetitive patterns and favorable deconvolution of features overlaid in the one-dimensional mass spectrum. This special feature article reports on an up-to-date and theor. sound use of Kendrick plots as a data processing tool. The approach requires no prior knowledge of the sample but offers promising dynamic capabilities for visualizing, filtering, and sometimes assigning congested mass spectra. Examples of applications of the approach to polymers are discussed throughout the text, but the same tools can be readily extended to other applications, including the anal. of polymers present as pollutants/contaminants, and to other analytes incorporating a repetitive moiety, for example, oils or lipids. In each of these instances, data processing can benefit from the application of an updated and interactive Kendrick anal.
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    18. 18
      Smith, J. S.; Laskin, A.; Laskin, J. Molecular Characterization of Biomass Burning Aerosols Using High-Resolution Mass Spectrometry. Anal. Chem. 2009, 81 (4), 1512– 1521,  DOI: 10.1021/ac8020664
      18
      Molecular Characterization of Biomass Burning Aerosols Using High-Resolution Mass Spectrometry
      Smith, Jeffrey S.; Laskin, Alexander; Laskin, Julia
      Analytical Chemistry (Washington, DC, United States) (2009), 81 (4), 1512-1521CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Chem. characterization of atm. aerosols presents a serious anal. challenge due to the complexity of particulate matter analytes composed of a large no. of compds. with a range of mol. structures, physicochem. properties, and reactivity. The chem. compn. of org. constituents of biomass burning aerosol (BBA) was characterized by high-resoln. electro-spray ionization mass spectrometry (ESI/MS). Accurate mass measurement combined with Kendrick anal. assigned an elemental compn. for hundreds of compds. in the 50-1000 m/z value range. ESI/MS spectra of different BBA samples contain a variety of distinct, sample-specific, characteristic peaks which can be used as unique markers for different types of biofuels. Results indicated a significant no. of high mol. wt. org. compds. in BBA samples were highly oxidized polar species which can be efficiently detected by ESI/MS but which are difficult to observe using conventional gas-chromatog./mass spectrometry aerosol sample anal. More than 70% of identified species have not been reported in the literature. Detected org. compds. exhibited a clear increase in the degree of satn., since the mol. wt. of analyte mols. increased. This increase was particularly pronounced for samples contg. a large no. of the CH2-based homologous series.
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    19. 19
      Lerno, L. A.; German, J. B.; Lebrilla, C. B. Method for the Identification of Lipid Classes Based on Referenced Kendrick Mass Analysis. Anal. Chem. 2010, 82 (10), 4236– 4245,  DOI: 10.1021/ac100556g
      19
      Method for the Identification of Lipid Classes Based on Referenced Kendrick Mass Analysis
      Lerno, Larry A., Jr.; German, J. Bruce; Lebrilla, Carlito B.
      Analytical Chemistry (Washington, DC, United States) (2010), 82 (10), 4236-4245CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      A rapid method for the detn. of lipid classes with high sensitivity is described. The referenced Kendrick mass defect (RKMD) and RKMD plots are novel adaptations of the Kendrick mass defect anal. that allows for the rapid identification of members of a homologous series in addn. to identifying the lipid class. Assignment of lipid classes by the RKMD method is accomplished by conversion of the lipid masses to the Kendrick mass scale and then referencing the converted masses to each lipid class. Referencing of the masses to a given lipid class is achieved by first subtracting the heteroatom and lipid backbone contributions to the mass defect, leaving behind the contribution to the mass by the fatty acid constituents. The final step in the referencing makes use of spacing differences in mass defects between members of the same Kendrick class to identify members of the lipid class being referenced. The end result of this is that a lipid belonging to the class being referenced will have an integer RKMD with the value of the integer being the degrees of unsatn. in the lipid. The RKMD method was able to successfully identify the lipids in an idealized data set consisting of 160 lipids drawn from the glyceride and phosphoglyceride classes. As a real world example the lipid ext. from bovine milk was analyzed using both accurate mass measurements and the RKMD method.
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    20. 20
      Kune, C.; McCann, A.; Raphaël, L. R.; Arias, A. A.; Tiquet, M.; Van Kruining, D.; Martinez, P. M.; Ongena, M.; Eppe, G.; Quinton, L.; Far, J.; De Pauw, E. Rapid Visualization of Chemically Related Compounds Using Kendrick Mass Defect As a Filter in Mass Spectrometry Imaging. Anal. Chem. 2019, 91 (20), 13112– 13118,  DOI: 10.1021/acs.analchem.9b03333
      20
      Rapid Visualization of Chemically Related Compounds Using Kendrick Mass Defect As a Filter in Mass Spectrometry Imaging
      Kune, Christopher; McCann, Andrea; Raphael, La Rocca; Arias, Anthony Arguelles; Tiquet, Mathieu; Van Kruining, Daan; Martinez, Pilar Martinez; Ongena, Marc; Eppe, Gauthier; Quinton, Loic; Far, Johann; De Pauw, Edwin
      Analytical Chemistry (Washington, DC, United States) (2019), 91 (20), 13112-13118CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Kendrick mass defect (KMD) anal. is widely used for helping the detection and identification of chem. related compds. based on exact mass measurements. We report here the use of KMD as a criterion for filtering complex mass spectrometry data set. The method allow automated, easy and efficient data processing, enabling the reconstruction of 2D distributions of families of homologous compds. from MSI images. We show that KMD filtering, based on inhouse software, is suitable and robust for high resoln. (full width at half-max., fwhm, at m/z 410 of 20 000) and very high-resoln. (fwhm, at m/z 410 of 160 000) MSI data. This method has been successfully applied to two different types of samples, bacteria cocultures, and brain tissue sections.
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    21. 21
      Anstett, A.; Chu, F.; Alonso, D. E.; Smith, R. W. Characterization of 2C-Phenethylamines Using High-Resolution Mass Spectrometry and Kendrick Mass Defect Filters. Forensic Chemistry 2018, 7, 47– 55,  DOI: 10.1016/j.forc.2017.12.006
      21
      Characterization of 2C-phenethylamines using high-resolution mass spectrometry and Kendrick mass defect filters
      Anstett, Alexandria; Chu, Fanny; Alonso, David E.; Smith, Ruth Waddell
      Forensic Chemistry (2018), 7 (), 47-55CODEN: FCOHAQ; ISSN:2468-1709. (Elsevier B.V.)
      The identification of synthetic designer drugs is challenging due to the high degree of structural similarity among compds. within a given class. In efforts to circumvent current legislation, new designer drug analogs that appear on the market have the same core structure as a regulated compd. but differ only in the position or the identity of a single substituent. Ref. stds. of the new analogs are not immediately available for comparison, making identification using conventional gas chromatog.-mass spectrometry (GC-MS) methods more challenging. In this work, the potential of mass defect to characterize compds. according to structural subclass was investigated. This initial work focused on synthetic phenethylamines, with the development of mass defect filters to characterize compds. as 2,5-dimethoxy-phenethylamines (2C-phenethylamines). Three sets of phenethylamines, including 2C-, aminopropylbenzofuran (APB-), and 2,5-dimethoxy-N-(2-methoxybenzyl) (NBOMe-) phenethylamines, were analyzed by GC-time-of-flight mass spectrometry (GC-TOFMS), using different instruments and under different conditions. The resulting accurate mass data were used to develop Kendrick mass defect filters based on the mol. ion and common neutral losses obsd. in a training set of 2C-phenethylamines. Successful characterization of test set compds. as 2C-phenethylamines with distinction from other structurally similar phenethylamines was demonstrated using the mol. ion and neutral loss mass defect filters.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXpvVKjsb4%253D&md5=33b0f6b118a5ad774eec93aa9de1fc34
    22. 22
      Archer, N. E.; Charles, Y.; Elliott, J. A.; Jickells, S. Changes in the Lipid Composition of Latent Fingerprint Residue with Time after Deposition on a Surface. Forensic Science International 2005, 154 (2–3), 224– 239,  DOI: 10.1016/j.forsciint.2004.09.120
      22
      Changes in the lipid composition of latent fingerprint residue with time after deposition on a surface
      Archer, Nia E.; Charles, Yannis; Elliott, Julia A.; Jickells, Sue
      Forensic Science International (2005), 154 (2-3), 224-239CODEN: FSINDR; ISSN:0379-0738. (Elsevier Ltd.)
      The work described in this report was focused on generating increased knowledge of fingerprint chem., particularly the compn. of a latent fingerprint at the time it is deposited, and the chem. changes in lipid components that occur over time. Fingerprints from 5 male donors (aged 25-34 years) were collected and aged under controlled conditions. The prints were then sampled at set intervals, solvent extd. with dichloromethane, co-derivatized with MSTFA and analyzed by gas chromatog.-mass spectrometry (GC-MS). It was shown that there was loss of squalene from prints stored in the light or in the dark. Loss was more rapid in the light, with squalene in prints from some donors not detected after 9 days storage. For these same donors, squalene was still detected after 33 days storage in the dark, but at much lower levels than in fresh prints. For satd. fatty acids (tetradecanoic, palmitic and stearic acid) there was a trend towards an increase in levels of these substances during storage (up to about 20 days) followed by a decrease back to original levels or below. This was the case for samples stored in the light or in the dark. For palmitoleic acid, a similar trend was seen. For oleic acid, this trend was seen for samples stored in the dark. For samples stored in the light the general trend was a decrease in level over the storage period (up to 33 days).
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    23. 23
      Dorakumbura, B. N.; Busetti, F.; Lewis, S. W. Analysis of Squalene and Its Transformation By-Products in Latent Fingermarks by Ultrahigh-Performance Liquid Chromatography-High Resolution Accurate Mass OrbitrapTM Mass Spectrometry. Forensic Chemistry 2020, 17, 100193,  DOI: 10.1016/j.forc.2019.100193
      23
      Analysis of squalene and its transformation by-products in latent fingermarks by ultrahigh-performance liquid chromatography-high resolution accurate mass Orbitrap mass spectrometry
      Dorakumbura, Buddhika N.; Busetti, Francesco; Lewis, Simon W.
      Forensic Chemistry (2020), 17 (), 100193CODEN: FCOHAQ; ISSN:2468-1709. (Elsevier B.V.)
      Transformation of squalene and its byproducts in latent fingermarks over time under different storage conditions (light, dark, and underwater) was examd. through ultrahigh-performance liq. chromatog.-high resoln. accurate mass Orbitrap mass spectrometry. Complications of assessing fingermark compositional variation over time using multiple samples with varying initial compns. were elucidated and a more rational approach was successfully demonstrated. Squalene was detected in all fresh natural fingermarks deposited on non-porous surfaces and the amt. ranged between 0.20 and 11.32μg/5 fingertips. A notable difference in the transformation of squalene was obsd. with different storage conditions, where a dark aquatic environment accelerated degrdn. of squalene compared to dark but dry conditions. Squalene monohydroperoxide was extremely short-lived in natural deposits while the amt. of squalene epoxide was still increasing relative to the initial amt., after ageing under dark and aquatic conditions for up to 7 days. Some oxidn. byproducts of cholesterol were also tentatively identified, which exhibited a growth over time against their initial concn. under any of the storage condition tested. These byproducts, therefore, show potential as biomarkers for targeted visualisation of aged deposits.
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    24. 24
      Poad, B. L. J.; Pham, H. T.; Thomas, M. C.; Nealon, J. R.; Campbell, J. L.; Mitchell, T. W.; Blanksby, S. J. Ozone-Induced Dissociation on a Modified Tandem Linear Ion-Trap: Observations of Different Reactivity for Isomeric Lipids. J. Am. Soc. Mass Spectrom. 2010, 21 (12), 1989– 1999,  DOI: 10.1016/j.jasms.2010.08.011
      24
      Ozone-Induced Dissociation on a Modified Tandem Linear Ion-Trap: Observations of Different Reactivity for Isomeric Lipids
      Poad, Berwyck L. J.; Pham, Huong T.; Thomas, Michael C.; Nealon, Jessica R.; Campbell, J. Larry; Mitchell, Todd W.; Blanksby, Stephen J.
      Journal of the American Society for Mass Spectrometry (2010), 21 (12), 1989-1999CODEN: JAMSEF; ISSN:1044-0305. (Elsevier B.V.)
      Ozone-induced dissocn. (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to det. the position(s) of unsatn. In this contribution, the authors describe the modification of a tandem linear ion-trap mass spectrometer specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides spatial sepn. between mass-selection, the ozonolysis reaction, and mass-anal. steps in the OzID process and thus delivers significant enhancements in speed and sensitivity (∼30-fold). These improvements allow spectra revealing the double-bond position(s) within unsatd. lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput lipidomic protocols. The stable ozone concn. afforded by this modified instrument also allows direct comparison of relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution position on the glycerol backbone, and (3) stereochem. For cis- and trans-isomers, differences were also obsd. in the branching ratio of product ions arising from the gas-phase ozonolysis reaction, suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Addnl. activation energy applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra contg. both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsatd. phosphatidylcholine within a cow brain lipid ext. provided evidence for up to four structurally distinct phospholipids differing in both double-bond position and sn-substitution.
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    25. 25
      Höring, M.; Ejsing, C. S.; Krautbauer, S.; Ertl, V. M.; Burkhardt, R.; Liebisch, G. Accurate Quantification of Lipid Species Affected by Isobaric Overlap in Fourier-Transform Mass Spectrometry. J. Lipid Res. 2021, 62, 100050,  DOI: 10.1016/j.jlr.2021.100050
      25
      Accurate quantification of lipid species affected by isobaric overlap in Fourier-transform mass spectrometry
      Horing Marcus; Krautbauer Sabrina; Ertl Verena M; Burkhardt Ralph; Ejsing Christer S; Liebisch Gerhard
      Journal of lipid research (2021), 62 (), 100050 ISSN:.
      Lipidomics data require consideration of ions with near-identical masses, which comprises among others the Type-II isotopic overlap. This overlap occurs in series of lipid species differing only by number of double bonds (DBs) mainly because of the natural abundance of (13)C-atoms. High-resolution mass spectrometry, such as Fourier-transform mass spectrometry (FTMS), is capable of resolving Type-II overlap depending on mass resolving power. In this work, we evaluated FTMS quantification accuracy of lipid species affected by Type-II overlap. Spike experiments with lipid species pairs of various lipid classes were analyzed by flow injection analysis-FTMS. Accuracy of quantification was evaluated without and with Type-II correction (using relative isotope abundance) as well as utilizing the first isotopic peak (M+1). Isobaric peaks, which were sufficiently resolved, were most accurate without Type-II correction. In cases of partially resolved peaks, we observed peak interference causing distortions in mass and intensity, which is a well-described phenomenon in FTMS. Concentrations of respective species were more accurate when calculated from M+1. Moreover, some minor species, affected by considerable Type-II overlap, could only be quantified by M+1. Unexpectedly, even completely unresolved peaks were substantially overcorrected by Type-II correction because of peak interference. The described method was validated including intraday and interday precisions for human serum and fibroblast samples. Taken together, our results show that accurate quantification of lipid species by FTMS requires resolution-depended data analysis.
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    26. 26
      Zhou, Y.; Park, H.; Kim, P.; Jiang, Y.; Costello, C. E. Surface Oxidation under Ambient Air─Not Only a Fast and Economical Method to Identify Double Bond Positions in Unsaturated Lipids But Also a Reminder of Proper Lipid Processing. Anal. Chem. 2014, 86 (12), 5697– 5705,  DOI: 10.1021/ac404214a
      26
      Surface Oxidation under Ambient Air - Not Only a Fast and Economical Method to Identify Double Bond Positions in Unsaturated Lipids But Also a Reminder of Proper Lipid Processing
      Zhou, Ying; Park, Hyejung; Kim, Philseok; Jiang, Yan; Costello, Catherine E.
      Analytical Chemistry (Washington, DC, United States) (2014), 86 (12), 5697-5705CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      A simple, fast approach elucidated carbon-carbon double bond positions in unsatd. lipids. Lipids were deposited onto various surfaces and the products from their oxidn. in ambient air were obsd. by electrospray ionization (ESI) mass spectrometry (MS). The most common oxidative products, aldehydes, were detected as transformations at the cleaved double bond positions. Ozonides and carboxylic acids were generated in certain lipids. Studies of the conditions controlling the appearance of these products indicated that the surface oxidn. depends on light and ambient air. Since the lipid oxidn. was slower in a high concn. of ozone, singlet oxygen appeared to be a parallel oxidant for unsatd. lipids. The 3-hydroxyl group in the sphingoid base of sulfatides offered some protection from oxidn. for the Δ4,5-double bond, slowing its oxidn. rate relative to that of the isolated double bond in the N-linked fatty acyl chain. Direct sampling by thin-layer chromatog. (TLC)-ESI-MS provides a powerful approach to elucidate detailed structural information on biol. samples. Co-localization of the starting lipids and their oxidn. products after TLC sepn. allowed assignment of the native unsatn. sites. Phosphatidylserine and N,N-di-Me phosphatidylethanolamine isomers in a bovine brain total lipid ext. were distinguished on the basis of their oxidn. products. Meanwhile, the findings reported herein reveal a potential pitfall in the assignment of structures to lipids extd. from TLC plates because of artifactual oxidn. after the plate development.
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    27. 27
      Weiny, J. A.; Boeglin, W. E.; Calcutt, M. W.; Stec, D. F.; Brash, A. R. Monolayer Autoxidation of Arachidonic Acid to Epoxyeicosatrienoic Acids as a Model of Their Potential Formation in Cell Membranes. J. Lipid Res. 2022, 63 (1), 100159,  DOI: 10.1016/j.jlr.2021.100159
      27
      Monolayer autoxidation of arachidonic acid to epoxyeicosatrienoic acids as a model of their potential formation in cell membranes
      Weiny, James A.; Boeglin, William E.; Calcutt, M. Wade; Stec, Donald F.; Brash, Alan R.
      Journal of Lipid Research (2022), 63 (1), 100159CODEN: JLPRAW; ISSN:1539-7262. (Elsevier Inc.)
      In light of the importance of epoxyeicosatrienoic acids (EETs) in mammalian pathophysiol., a nonenzymic route that might form these monoepoxides in cells is of significant interest. In the late 1970s, a simple system of arranging linoleic acid mols. on a monolayer on silica was devised and shown to yield monoepoxides as the main autoxidn. products. Here, we investigated this system with arachidonic acid and characterized the primary products. By the early stages of autoxidn. (∼10% conversion of arachidonic acid), the major products detected by LC-MS and HPLC-UV were the 14,15-, 11,12-, and 8,9-EETs, with the 5,6-EET mainly represented as the 5-δ-lactone-6-hydroxyeicosatrienoate as established by 1H-NMR. The EETs were mainly the cis epoxides as expected, with minor trans configuration EETs among the products. 1H-NMR anal. in four deuterated solvents helped clarify the epoxide configurations. EET formation in monolayers involves intermol. reaction with a fatty acid peroxyl radical, producing the EET and leaving an incipient and more reactive alkoxyl radical, which in turn gives rise to epoxy-hydro(pero)xides and other polar products. The monolayer alignment of fatty acid mols. resembles the arrangements of fatty acids in cell membranes and, under conditions of lipid peroxidn., this intermol. mechanism might contribute to EET formation in biol. membranes.
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    28. 28
      Wu, G.-S.; Stein, R. A.; Mead, J. F. Autoxidation of Fatty Acid Monolayers Adsorbed on Silica Gel: II. Rates and Products. Lipids 1977, 12 (11), 971– 978,  DOI: 10.1007/BF02533320
      28
      Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products
      Wu, Guey-Shuang; Stein, Robert A.; Mead, James F.
      Lipids (1977), 12 (11), 971-8CODEN: LPDSAP; ISSN:0024-4201.
      Unsatd. fatty acid monolayers on silica gel were autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies were studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60°. The rates of autoxidn. of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates were considerably faster than that in bulk phase. The rates conformed to apparent 1st-order kinetics. Autoxidn. of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amt. of diene conjugation. The major products formed were 9,10-epoxy- and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidn. was stereospecific, with cis- and trans-olefins giving cis- and trans-epoxides, resp. Oleic acid was autoxidized to only a small extent during 27 h and produced no detectable amt. of epoxide.
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    29. 29
      Mountfort, K. A.; Bronstein, H.; Archer, N.; Jickells, S. M. Identification of Oxidation Products of Squalene in Solution and in Latent Fingerprints by ESI-MS and LC/APCI-MS. Anal. Chem. 2007, 79 (7), 2650– 2657,  DOI: 10.1021/ac0623944
      29
      Identification of Oxidation Products of Squalene in Solution and in Latent Fingerprints by ESI-MS and LC/APCI-MS
      Mountfort, Katrina A.; Bronstein, Hugo; Archer, Nia; Jickells, Sue M.
      Analytical Chemistry (Washington, DC, United States) (2007), 79 (7), 2650-2657CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      An investigation was carried out to identify oxidn. products of squalene (SQ) in latent fingerprints. Oxidn. products of SQ incubated in soln. with Rose Bengal as a photooxidizer were isolated by semipreparative HPLC-UV and identified by direct infusion ESI-MS and flow injection APCI-MS. Squalene hydroperoxides ranging from squalene monohydroperoxide (SQ-[OOH]) to SQ-[OOH]5 were identified together with SQ epoxide. SQ-[OOH] was the main oxidn. product. An LC/APCI-MS method was developed and used to monitor the fate of SQ in soln. and in latent fingerprints and the formation of SQ-[OOH] and SQ epoxide. SQ-[OOH] and SQ epoxide were detected in freshly deposited prints but increased markedly after 1 day and continued to increase up to 5 days after print deposition. By day 7, these substances could no longer be detected in prints. SQ was rapidly depleted from prints such that by day 7 it was no longer detected. A similar pattern was seen for SQ stored in the light in dichloromethane but with a slower formation of SQ-[OOH] and SQ epoxide. The oxidn. of SQ in soln. in the presence and absence of photooxidizer was shown by TLC to proceed as follows: SQ → SQ-[OOH] + SQ epoxide. SQ-[OOH] → SQ-[OOH]2 → SQ-[OOH]3 → SQ-[OOH]4 + SQ-[OOH]5, with oxidn. being more rapid in the presence of photooxidizer. SQ-[OOH]4 and SQ-[OOH]5 could still be detected at 20 days in a soln. of SQ aged in soln. in the absence of photooxidizer. The oxidn. products of SQ should make suitable targets for development of new reagents for visualizing latent fingerprints in forensic science.
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    30. 30
      Grüneis, V.; Fruehwirth, S.; Zehl, M.; Ortner, J.; Schamann, A.; König, J.; Pignitter, M. Simultaneous Analysis of Epoxidized and Hydroperoxidized Triacylglycerols in Canola Oil and Margarine by LC-MS. J. Agric. Food Chem. 2019, 67 (36), 10174– 10184,  DOI: 10.1021/acs.jafc.9b03601
      30
      Simultaneous Analysis of Epoxidized and Hydroperoxidized Triacylglycerols in Canola Oil and Margarine by LC-MS
      Grueneis, Verena; Fruehwirth, Sarah; Zehl, Martin; Ortner, Johanna; Schamann, Alexandra; Koenig, Juergen; Pignitter, Marc
      Journal of Agricultural and Food Chemistry (2019), 67 (36), 10174-10184CODEN: JAFCAU; ISSN:0021-8561. (American Chemical Society)
      The progress of lipid oxidn. in foods is evaluated by measuring the peroxides and their scission products. However, hydrogen abstraction-independent pathways are not considered by commonly applied methods despite the known reactivity of epoxides towards biomols. Herein, a novel LC-MS/MS method was developed to detect hydroperoxidized and epoxidized triacylglycerols (TAGs) without derivatization or hydrolyzation of food samples. Epoxidized TAGs could be detected in refined canola oil at concns. of 96.8±2.08μM, while only 5.77±0.04μM hydroperoxidized TAGs could be detd. In contrast to canola oil, margarine was more resistant to lipid oxidn. since generation of epoxidized TAGs could only be marginally enhanced from 21.7±0.48μM to 28.8±0.64μM in margarine after treatment at 180°C for 60 min, as also reflected by a peroxide value of 0.80±0.00 meq O2/kg, which remained unchanged. The new method allows the assessment of food safety by the simultaneous measurement of hydroperoxidized and epoxidized TAGs without hydrolysis and laborious sample prepn.
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    31. 31
      Sevanian, A.; Mead, J. F.; Stein, R. A. Epoxides as Products of Lipid Autoxidation in Rat Lungs. Lipids 1979, 14 (7), 634– 643,  DOI: 10.1007/BF02533449
      31
      Epoxides as products of lipid autoxidation in rat lungs
      Sevanian, Alex; Mead, James F.; Stein, Robert A.
      Lipids (1979), 14 (7), 634-43CODEN: LPDSAP; ISSN:0024-4201.
      The nature and content of lipid epoxides in rat lung were examd. in air-breathing control rats and in those exposed to NO2. Exposure to 6.5 ppm NO2 for 24 h resulted in significantly greater epoxide content in a no. of lipid classes. Apparently, exposure to oxidizing gases can lead to an accumulation of lipid epoxides in both lung parenchymal tissue and on the alveolar surface.
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    32. 32
      Butovich, I. A.; Wojtowicz, J. C.; Molai, M. Human Tear Film and Meibum. Very Long Chain Wax Esters and (O-Acyl)-Omega-Hydroxy Fatty Acids of Meibum. J. Lipid Res. 2009, 50 (12), 2471– 2485,  DOI: 10.1194/jlr.M900252-JLR200
      32
      Human tear film and meibum. Very long chain wax esters and (O-acyl)-omega-hydroxy fatty acids of meibum
      Butovich, Igor A.; Wojtowicz, Jadwiga C.; Molai, Mike
      Journal of Lipid Research (2009), 50 (12), 2471-2485CODEN: JLPRAW; ISSN:0022-2275. (American Society for Biochemistry and Molecular Biology, Inc.)
      Human meibum was targetly analyzed for the presence of intact wax esters (WEs) and related compds. by means of reverse-phase HPLC in combination with ion trap mass spectrometry. The major detected WEs were based on C18:n (n = 1-4) unsatd. FAs ranking in the following order of abundance: C18:1>C18:2>C18:3>C18:4. The major fatty alcs. (FAls) found in WE were of satd. nature and varied from C18:0 to C28:0. The three most abundant species were C18:1-FA esters of C24:0, C25:0, and C26:0-FAl. Typically, a major compd. based on C18:1-FA and a satd. FAl was accompanied by a few related compds. based on a C18:2, C18:3, and C18:4-FA. Contrary to previous reports, no epoxy-WEs or epoxy-FAs were detected in fresh and 1-yr-old meibum samples. More than 20 (O-acyl)-ω-hydroxy-FAs (OAHFAs) were obsd. The main detected OAHFAs were based on very long-chain ω-hydroxy-FA (C30:1, C32:1, and C34:1) acylated through their ω-hydroxyls by a C18:1-FA. Due to their amphiphilic anionogenic nature, OAHFAs may be responsible for stabilization of the tear film lipid layer by creating an interface between the vast pool of strictly nonpolar lipids of meibum (WEs, cholesteryl esters, etc.) and the aq. subphase beneath it, a role previously attributed to phospholipids.
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    33. 33
      Eisenberg, W. C.; DeSilva, M. Atmospheric Gas Phase Generation of Singlet Oxygen by Homogeneous Photosensitization. Tetrahedron Lett. 1990, 31 (41), 5857– 5860,  DOI: 10.1016/S0040-4039(00)97978-4
      33
      Atmospheric gas phase generation of singlet oxygen by homogeneous photosensitization
      Eisenberg, Walter C.; DeSilva, Mutha
      Tetrahedron Letters (1990), 31 (41), 5857-60CODEN: TELEAY; ISSN:0040-4039.
      Singlet O was generated in the gas phase at atm. pressure using homogeneous photosensitization and an org. sensitizer such as benzene. The emission of O2 (1Δg) at 1.27 μm was obsd. providing a rapid and accurate method of evaluating sensitizers.
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    34. 34
      Shimizu, N.; Bersabe, H.; Ito, J.; Kato, S.; Towada, R.; Eitsuka, T.; Kuwahara, S.; Miyazawa, T.; Nakagawa, K. Mass Spectrometric Discrimination of Squalene Monohydroperoxide Isomers. J. Oleo Sci. 2017, 66 (3), 227– 234,  DOI: 10.5650/jos.ess16159
      34
      Mass spectrometric discrimination of squalene monohydroperoxide isomers
      Shimizu, Naoki; Bersabe, Hannah; Ito, Junya; Kato, Shunji; Towada, Ryo; Eitsuka, Takahiro; Kuwahara, Shigefumi; Miyazawa, Teruo; Nakagawa, Kiyotaka
      Journal of Oleo Science (2017), 66 (3), 227-234CODEN: JOSOAP; ISSN:1345-8957. (Japan Oil ChemistsÏ Society)
      Squalene (SQ), a main component of human sebum, is readily photooxidized by exposure to sunlight, producing six squalene monohydroperoxide (SQ-OOH) isomers. Despite its known connection to various skin conditions, few studies have sought to analyze SQ-OOH at the isomeric level. In this study, we aimed to develop a method to discriminate each SQ-OOH isomer with the use of tandem mass spectrometry (MS/MS). The six std. SQ-OOH isomers were prepd. by photooxidizing SQ in the presence of rose bengal, a photosensitizer, and isolated by semipreparative high-performance liq. chromatog. (HPLC). To purify each isomer, 2-methoxypropene, which reversibly reacts with the hydroperoxide group of SQ-OOH, was utilized. Product ion scanning was then performed on the std. SQ-OOH isomers in the absence and presence of the sodium ion. In the absence of the sodium ion, the fragmentation patterns produced by atm. pressure chem. ionization were similar between the isomers, whereas in the presence of the sodium ion by electrospray ionization, unique fragmentation patterns were achieved. Based on these fragment ions, HPLC-MS/MS multiple reaction monitoring anal. was conducted on a mixt. of the std. SQ-OOH isomers. We achieved discrimination of SQ-OOH isomers with high selectivity and detected SQ-OOH isomers at nanogram levels. These results may improve our understanding of the effect of SQ-OOH on skin conditions as well as the mechanism behind SQ peroxidn.
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    35. 35
      Jones, I. T. N.; Wayne, R. P. Photolysis of Ozone by 254-, 313-, and 334-nm Radiation. J. Chem. Phys. 1969, 51 (8), 3617– 3618,  DOI: 10.1063/1.1672561
      35
      Photolysis of ozone by 254-, 313-, and 334-nm radiation
      Jones, Ian Thomas Nisbet; Wayne, Richard P.
      Journal of Chemical Physics (1969), 51 (8), 3617-18CODEN: JCPSA6; ISSN:0021-9606.
      The title process was studied at 25°. The photolysis at 254 nm gives O(1D) and singlet O2. At 313 nm singlet O2 is still produced, but most of the O atoms are O(3P), and at 334 nm the primary products are exclusively O(3P) and singlet O2. The primary steps at 313 and 334 nm appear not to give spin-conserved products, suggesting that spin-conservation rules may not apply when absorption is weak.
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    36. 36
      Pitts, J. N.; Khan, A. U.; Smith, E. B.; Wayne, R. P. Singlet Oxygen in the Environmental Sciences. Singlet Molecular Oxygen and Photochemical Air Pollution. Environ. Sci. Technol. 1969, 3 (3), 241– 247,  DOI: 10.1021/es60026a004
      36
      Singlet oxygen in the environmental sciences. Singlet molecular oxygen and photochemical air pollution
      Pitts, James N., Jr.; Khan, Ahsan U.; Smith, E. Brian; Wayne, Richard P.
      Environmental Science and Technology (1969), 3 (3), 241-7CODEN: ESTHAG; ISSN:0013-936X.
      Singlet mol. O (1O2) may play a significant role as an oxidant in photochem. air pollution. Reaction of electronically excited O with olefinic substances produces thermally unstable hydroperoxides which may be involved in the rapid conversion of NO into NO2, a process not well understood in photochem. air pollution. Several mechanisms for the formation of 1O are examd. crit. in relation to their possible importance in the chemistry of urban atm. In each, the excitation energy is derived ultimately from the sun's radiation, but the energy may be utilized by direct absorption of radiation by ground state 3O2, by photolysis of an atm. contaminant to form excited 1O2 in the primary step, by spin-conserved energy transfer mechanism in which an atm. contaminant absorbs solar radiation and transfers its excitation to ground state 3O2, or by exothermic chem. reactions involving atm. contaminants which themselves originated in a photochem. process.
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    37. 37
      Bednařík, A.; Bölsker, S.; Soltwisch, J.; Dreisewerd, K. An On-Tissue Paternò-Büchi Reaction for Localization of Carbon-Carbon Double Bonds in Phospholipids and Glycolipids by Matrix-Assisted Laser-Desorption-Ionization Mass-Spectrometry Imaging. Angew. Chem. Int. Ed 2018, 57 (37), 12092– 12096,  DOI: 10.1002/anie.201806635
      37
      An On-Tissue Paterno-Buechi Reaction for Localization of Carbon-Carbon Double Bonds in Phospholipids and Glycolipids by Matrix-Assisted Laser-Desorption-Ionization Mass-Spectrometry Imaging
      Bednarik, Antonin; Boelsker, Stefan; Soltwisch, Jens; Dreisewerd, Klaus
      Angewandte Chemie, International Edition (2018), 57 (37), 12092-12096CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) visualizes the distribution of phospho- and glycolipids in tissue sections. However, C=C double-bond (db) positional isomers generally cannot be distinguished. Now an on-tissue Paterno-Buechi (PB) derivatization procedure that exploits benzaldehyde as a MALDI-MSI-compatible reagent is introduced. Laser-induced postionization (MALDI-2) was used to boost the yields of protonated PB products. Collision-induced dissocn. of these species generated characteristic ion pairs, indicative of C=C position, for numerous singly and polyunsatd. phospholipids and glycosphingolipids in mouse brain tissue. Several db-positional isomers of phosphatidylcholine and phosphatidylserine species were expressed with highly differential levels in the white and gray matter areas of cerebellum. Our PB-MALDI-MS/MS procedure could help to better understand the physiol. role of these db-positional isomers.
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    38. 38
      Pappas, A. Epidermal Surface Lipids. Derm.-Endocrinol. 2009, 1 (2), 72– 76,  DOI: 10.4161/derm.1.2.7811
      38
      Epidermal surface lipids
      Pappas, Apostolos
      Dermato-Endocrinology (2009), 1 (2), 72-76CODEN: DERMFJ; ISSN:1938-1972. (Landes Bioscience)
      A review. A layer of lipids, which are of both sebaceous and keratinocyte origin, covers the surface of the skin. The apparent compn. of surface lipids varies depending on the selected method of sampling. Lipids produced by the epidermal cells are an insignificant fraction of the total extractable surface lipid on areas rich in sebaceous glands. Due to the holocrine activity of the sebaceous gland, its product of secretion (sebum) is eventually released to the surface of the skin and coats the fur as well. Lipids of epidermal origin fill the spaces between the cells, like mortar or cement. The sebaceous lipids are primarily non polar lipids as triglycerides, wax esters and squalene, while epidermal lipids are a mixt. of ceramides, free fatty acids and cholesterol. The compn. of the sebaceous lipids is unique and intriguing and elevated sebum excretion is a major factor involved in the pathophysiol. of acne. Recent studies have elucidated the roles that epidermal surface lipids have on normal skin functions and acne.
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    39. 39
      Roopashree, P. G.; Shetty, S. S.; Suchetha Kumari, N. Effect of Medium Chain Fatty Acid in Human Health and Disease. Journal of Functional Foods 2021, 87, 104724,  DOI: 10.1016/j.jff.2021.104724
      39
      Effect of medium chain fatty acid in human health and disease
      Roopashree, P. G.; Shetty, Shilpa S.; Suchetha Kumari, N.
      Journal of Functional Foods (2021), 87 (), 104724CODEN: JFFOAX; ISSN:1756-4646. (Elsevier Ltd.)
      Medium chain fatty acids (MCFAs) has unique transport system and is rapidly metabolized in the body. It mainly occurs in coconut oil, palm kernel oil and milk products. Dietary supplementation with MCFAs can improve metabolic features as well as cognition in humans. Some of the effects of MCFAs may be through direct receptor-mediated intracellular pathways, but MCFAs are also metabolic regulators that can alter circulating levels of hormones and metabolites, and hence may indirectly mediate body metab. Here we describe how dietary medium chain fatty acid, previously found to improve immune response and insulin secretion via G-protein coupled receptors, can increase apoptosis in cancer cells through the activation of the EGFR/ERK/AP1 transduction pathway. MCFA-enriched diets could therefore be used to manage metabolic diseases through the modification of gut microbiota, activation of GPR 40 and GPR 84.
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    40. 40
      Belov, M. E.; Ellis, S. R.; Dilillo, M.; Paine, M. R. L.; Danielson, W. F.; Anderson, G. A.; de Graaf, E. L.; Eijkel, G. B.; Heeren, R. M. A.; McDonnell, L. A. Design and Performance of a Novel Interface for Combined Matrix-Assisted Laser Desorption Ionization at Elevated Pressure and Electrospray Ionization with Orbitrap Mass Spectrometry. Anal. Chem. 2017, 89 (14), 7493– 7501,  DOI: 10.1021/acs.analchem.7b01168
      40
      Design and Performance of a Novel Interface for Combined Matrix-Assisted Laser Desorption Ionization at Elevated Pressure and Electrospray Ionization with Orbitrap Mass Spectrometry
      Belov, Mikhail E.; Ellis, Shane R.; Dilillo, Marialaura; Paine, Martin R. L.; Danielson, William F.; Anderson, Gordon A.; de Graaf, Erik L.; Eijkel, Gert B.; Heeren, Ron M. A.; McDonnell, Liam A.
      Analytical Chemistry (Washington, DC, United States) (2017), 89 (14), 7493-7501CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Matrix-Assisted Laser Desorption Ionization, MALDI, has been increasingly used in a variety of biomedical applications, including tissue imaging of clin. tissue samples, and in drug discovery and development. These studies strongly depend on the performance of the anal. instrumentation and would drastically benefit from improved sensitivity, reproducibility, and mass/spatial resoln. In this work, we report on a novel combined MALDI/ESI interface, which was coupled to different Orbitrap mass spectrometers (Elite and Q Exactive Plus) and extensively characterized with peptide and protein stds., and in tissue imaging expts. In our approach, MALDI is performed in the elevated pressure regime (5-8 Torr) at a spatial resoln. of 15-30 μm, while ESI-generated ions are injected orthogonally to the interface axis. We have found that introduction of the MALDI-generated ions into an electrodynamic dual-funnel interface results in increased sensitivity characterized by a limit of detection of ∼400 zmol, while providing a mass measurement accuracy of 1 ppm and a mass resolving power of 120 000 in anal. of protein digests. In tissue imaging expts., the MALDI/ESI interface has been employed in expts. with rat brain sections and was shown to be capable of visualizing and spatially characterizing very low abundance analytes sepd. only by 20 mDa. Comparison of imaging data has revealed excellent agreement between the MALDI and histol. images.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscentsci.2c00408.

    • Additional experimental details and discussion, unsubtracted mass spectra, various KMD plots, summary of PB results, type-II isotopic overlap, MS images, MS/MS of epoxides and PB product, TG epoxide profiles in various conditions, separation of O6 homologous series, and promising aging features over time (PDF)

    • Data files used in the KMD plots and the PB table (ZIP)

    • Transparent Peer Review report available (PDF)


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