Robust Solid-Contact Ion Selective Electrodes for High-Resolution In Situ Measurements in Fresh Water SystemsClick to copy article linkArticle link copied!
Abstract
Biogeochemical processes are often confined to very narrow zones in aquatic systems. Therefore, highly resolved in situ measurements are required to study these processes. Potentiometric solid-contact ion selective electrodes (SC-ISEs) are promising tools for such measurements. SC-ISEs show good performance in analyses under controlled experimental conditions. Very few sensor designs, however, can sustain the challenges of natural water matrices and external environmental conditions during in situ applications. We fabricated ammonium and pH selective SC-ISEs with functionalized multiwalled carbon nanotubes (f-MWCNT) as a solid contact. Their functionality was tested in the laboratory and applied in situ for vertical profiling in a eutrophic lake. Sensors were insensitive to strong redox changes, high sulfide concentrations, and bright daylight conditions during the application in the lake. In addition, sensors are easily fabricated and exhibit short response times (<10 s). The proposed design of SC-ISEs based on f-MWCNTs is quite suitable for high-resolution in situ profiling of ionic species in fresh water lakes.
Introduction
Materials and Methods
Sensor Design
Field Site
In Situ Profiling
In Situ Calibration

Results and Discussion
Figure 1
Figure 1. In situ profiles of dissolved oxygen, temperature, and total sulfide in July 2015 obtained simultaneously with the SC-ISE measurements in Lake Rotsee (A) and recorded by SC-ISEs to compare the performance of POT-based (red) and f-MWCNT-based (gray) ammonium sensors under dark conditions, where black circles represent ammonium concentrations in syringe samples taken simultaneously during the in situ profiling (B).
Figure 2
Figure 2. In situ profiles of dissolved oxygen concentration, temperature, and total sulfide in September 2015 obtained simultaneously with the SC-ISE measurements in Lake Rotsee (A) and recorded by SC-ISEs to extend the application to pH (green) measurements in addition to ammonium (gray) with f-MWCNT-based SC-ISEs in intense daylight, where black circles represent ammonium concentrations and green diamonds represent pH measurements in syringe samples taken simultaneously during the in situ profiling (B).
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.estlett.7b00130.
Experimental section with electrode fabrication, laboratory calibration (Figure S1), water-layer test (Figure S2), redox sensitivity test (Figure S3), uncertainty analysis (Figure S4), absolute error analysis (Figure S5), in situ profiling setup (Figure S6), in situ calibration parameters (Table S1), selectivity coefficients for ion selective membranes and mean concentrations of relevant ions in the lake water column (Table S2), and properties of SC-ISEs (Table S3) (PDF)
Terms & Conditions
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Acknowledgment
The authors are thankful for the financial support from the Swiss National Science Foundation (SNF Grant 147654).
References
This article references 28 other publications.
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- 3Athavale, R.; Kokorite, I.; Dinkel, C.; Bakker, E.; Wehrli, B.; Crespo, G. A.; Brand, A. In Situ Ammonium Profiling Using Solid-Contact Ion-Selective Electrodes in Eutrophic Lakes Anal. Chem. 2015, 87, 11990– 11997 DOI: 10.1021/acs.analchem.5b02424Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVGhs7vJ&md5=f45a56ee9162b8e04bddf8fd2018baa4In Situ Ammonium Profiling Using Solid-Contact Ion-Selective Electrodes in Eutrophic LakesAthavale, Rohini; Kokorite, Ilga; Dinkel, Christian; Bakker, Eric; Wehrli, Bernhard; Crespo, Gaston A.; Brand, AndreasAnalytical Chemistry (Washington, DC, United States) (2015), 87 (24), 11990-11997CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A promising profiling setup for in situ measurements in lakes with potentiometric solid-contact ion-selective electrodes (SC-ISEs) and a data processing method for sensor calibration and drift correction are presented. The profiling setup consists of a logging system, which is equipped with a syringe sampler and sensors for the measurement of std. parameters including temp., cond., O and photosynthetically active radiation (PAR). The setup was expanded with SC-ISEs in galvanically sepd. amplifiers. The potential for high-resoln. profiling is studied by deploying the setup in the eutrophic Lake Rotsee (Lucerne, Switzerland), using 2 different designs of ammonium sensing SC-ISEs. Ammonium was chosen as a target analyte, since it is the most common reduced inorg. N species involved in various pathways of the N cycle and is therefore indicative of numerous biogeochem. processes that occur in lakes such as denitrification and primary prodn. One of the designs, which uses a composite C-nanotube-PVC-based membrane, suffered from sulfide poisoning in the deeper, sulfidic regions of the lake. In contrast, electrodes contg. a plasticizer-free methacrylate copolymer-based sensing layer on top of a conducting polymer layer as a transducer did not show this poisoning effect. The syringe samples drawn during continuous profiling were utilized to calibrate the electrode response. Reaction hotspots and steep gradients of ammonium concns. were identified on-site by monitoring the electrode potential online. Upon conversion to high-resoln. concn. profiles, fine scale features between the calibration points were displayed, which would have been missed by conventional limnol. sampling and subsequent lab. analyses. Thus, the presented setup with SC-ISEs tuned to analytes of interest can facilitate the study of biogeochem. processes that occur at the centimeter scale.
- 4Sutter, J.; Radu, A.; Peper, S.; Bakker, E.; Pretsch, E. Solid-contact polymeric membrane electrodes with detection limits in the subnanomolar range Anal. Chim. Acta 2004, 523, 53– 59 DOI: 10.1016/j.aca.2004.07.016Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXnsVGgsb4%253D&md5=e1089328f8878a87ff653e2c1ebb4acaSolid-contact polymeric membrane electrodes with detection limits in the subnanomolar rangeSutter, Jolanda; Radu, Aleksandar; Peper, Shane; Bakker, Eric; Pretsch, ErnoeAnalytica Chimica Acta (2004), 523 (1), 53-59CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)Ion-selective electrode (ISE) membranes with a solid contact rather than a traditional liq. inner contact are anticipated to give lower detection limits because of diminished ion fluxes. Often, however, ill-defined solid contacts give rise to instabilities and interferences by O gas. Here, a poly(Me methacrylate)/poly(decyl methacrylate) (MMA/DMA) copolymer as membrane matrix was solvent-cast on a layer of poly(n-octyl)thiophene (POT) deposited on Au as internal contact. The resulting Ca2+- and Pb2+-selective electrodes were not sensitive to O2 and no evidence was found for the presence of a H2O film between membrane and internal contact. However, a H2O film was present when electropolymd. poly(n-octyl)thiophene was used. In the absence of a conducting polymer, O2 induced a significant change in the EMF but no clear evidence was found for a H2O film between POT and the MMA/DMA membrane. The lower detection limit of the new Au-POT-MMA/DMA solid-contact electrodes was somewhat better than that obsd. with a corresponding liq.-contact ISE and reached subnanomolar levels. Importantly, the response times for the solid-contact ISE are, at low concns., much faster than for the liq.-contact ISE.
- 5Crespo, G. A.; Macho, S.; Rius, F. X. Ion-selective electrodes using carbon nanotubes as ion-to-electron transducers Anal. Chem. 2008, 80, 1316– 1322 DOI: 10.1021/ac071156lGoogle Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsl2msA%253D%253D&md5=fb603684e62e06f6150085731e77f225Ion-Selective Electrodes Using Carbon Nanotubes as Ion-to-Electron TransducersCrespo, Gaston A.; Macho, Santiago; Rius, F. XavierAnalytical Chemistry (Washington, DC, United States) (2008), 80 (4), 1316-1322CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This study developed a new type of all-solid-state ion-selective electrode based on a transducing layer of a network of single-walled C nanotubes. The extraordinary capacity of C nanotubes to promote electron transfer between heterogeneous phases made the presence of electroactive polymers or any other ion-to-electron-transfer promoter unnecessary. The new transducer layer was characterized by environmental SEM and electrochem. impedance spectroscopy. The stability of the elec. potential of the new solid-contact electrode was examd. by performing current-reversal chronopotentiometry, and the influence of the interfacial H2O film was assessed by the potentiometric H2O layer test. The performance of the new electrode was evaluated by detg. K+ with an ion-selective membrane that contained the known valinomycin ion carrier. The new electrode had a Nernstian slope (58.4 mV/decade), dynamic ranges of four logarithmic units, and selectivities and limits of detection comparable to other solid-contact electrodes. The short response time (<10 s for activities >10-5.5 M) and the stability of the signal over several days makes these new electrodes very promising candidates for attaining true miniaturization.
- 6Bobacka, J.; Ivaska, A.; Lewenstam, A. Potentiometric ion sensors Chem. Rev. 2008, 108, 329– 351 DOI: 10.1021/cr068100wGoogle Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsl2qtA%253D%253D&md5=5bbaa0cbb71586bdbf5d93a140f4d743Potentiometric Ion SensorsBobacka, Johan; Ivaska, Ari; Lewenstam, AndrzejChemical Reviews (Washington, DC, United States) (2008), 108 (2), 329-351CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The aim of this review is to highlight some of these modern topics in the field of potentiometric ion sensors. This review is focused on recent achievements since the beginning of this millennium and emphasizes the results from the last 5 years (2002-2006). Section 2 gives a crit. overview, placed in a historical perspective, on the theory of the potentiometric response, including classical equil. models as well as advanced nonequil. models. Section 3 deals with recent advances in the field of solid-contact ion-selective electrodes (ISEs), emphasizing the application of conducting polymers as ion-to-electron transducers. Recent developments in the area of miniaturized ISEs, including applications in flow anal., life science, and biol., are discussed in section 4. Finally, the new wave of ISEs is commented on in section 5. The authors hope that the issues discussed will illustrate the great possibilities offered by modern ISEs and encourage further innovations in the rapidly expanding field of chem. sensors in the years to come.
- 7Bakker, E.; Pretsch, E. Modern Potentiometry Angew. Chem., Int. Ed. 2007, 46, 5660– 5668 DOI: 10.1002/anie.200605068Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXosFOkt7Y%253D&md5=36afcaafe768381e76bcc13983cbfd91Modern potentiometryBakker, Eric; Pretsch, ErnoeAngewandte Chemie, International Edition (2007), 46 (30), 5660-5668CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. A silent revolution of ion-selective electrodes (ISEs) took place during the past decade. Polymeric membrane electrodes are now routinely used to det. complex formation consts. between lipophilic guests and ionic hosts. Ultratrace level measurements have become possible even in samples of very small vols., with detection limits in the attomole range.
- 8Yuan, D.; Anthis, A. H. C.; Ghahraman Afshar, M.; Pankratova, N.; Cuartero, M.; Crespo, G. A.; Bakker, E. All-Solid-State Potentiometric Sensors with a Multiwalled Carbon Nanotube Inner Transducing Layer for Anion Detection in Environmental Samples Anal. Chem. 2015, 87, 8640– 8645 DOI: 10.1021/acs.analchem.5b01941Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlemurjO&md5=e0484a7b9d636d491402bcfb9953cd7cAll-Solid-State Potentiometric Sensors with a Multiwalled Carbon Nanotube Inner Transducing Layer for Anion Detection in Environmental SamplesYuan, Dajing; Anthis, Alexandre H. C.; Ghahraman Afshar, Majid; Pankratova, Nadezda; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2015), 87 (17), 8640-8645CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)While ion to electron transducing layers for the fabrication of potentiometric membrane electrodes for the detection of cations were well established, similar progress for the sensing of anions has not yet been realized. The authors report for this reason on a novel approach for the development of all-solid-state anion selective electrodes using lipophilic multiwalled carbon nanotubes (f-MWCNTs) as the inner ion to electron transducing layer. This material can be solvent cast, as it conveniently dissolves in THF, an important advantage to develop uniform films without the need for using surfactants that might deteriorate the performance of the electrode. Solid contact sensors for carbonate, nitrate, nitrite, and dihydrogen phosphate are fabricated and characterized, and all exhibit comparable anal. characteristics to the inner liq. electrodes. For example, the carbonate sensor exhibits a Nernstian slope of 27.2 ± 0.8 mV dec-1, a LOD = 2.3 μM, a response time of 1 s, a linear range of four logarithmic units, and a medium-term stability of 0.04 mV h-1 was obtained in a pH 8.6 buffered soln. Water layer test, reversibility, and selectivity for chloride, nitrate, and hydroxide are also reported. The excellent properties of f-MWCNTs as a transducer are contrasted to the deficient performance of poly(3-octyl-thiophene) (POT) for carbonate detection. This is evidenced both with a significant drift in the potentiometric measures as well as a pronounced sensitivity to light (either sunlight or artificial light). This latter aspect may compromise its potential for environmental in situ measurements (night/day cycles). The concn. of carbonate is detd. in a river sample (Arve river, Geneva) and compared to a ref. method (automatic titrator with potentiometric pH detection). Probably nanostructured materials such as f-MWCNTs are an attractive platform as a general ion-to-electron transducer for anion-selective electrodes.
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- 21Kharissova, O. V.; Kharisov, B. I.; de Casas Ortiz, E. G. Dispersion of carbon nanotubes in water and non-aqueous solvents RSC Adv. 2013, 3, 24812– 24852 DOI: 10.1039/c3ra43852jGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslCrs7fO&md5=9123dcbc01cfba4bc3775379cf85e7d1Dispersion of carbon nanotubes in water and non-aqueous solventsKharissova, Oxana V.; Kharisov, Boris I.; de Casas Ortiz, Edgar GerardoRSC Advances (2013), 3 (47), 24812-24852CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)A review. Contemporary methods for dispersion of carbon nanotubes in water and non-aq. media are discussed. Most attention is paid to ultrasonic and plasma techniques and other phys. techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and org. salts, mineral and org. acids, oxides, inorg. and org. peroxides, org. sulfonates, polymers, dyes, natural products, biomols., and coordination compds.). Special studies on CNTs solubilization are examd.
- 22Lindner, E.; Gyurcsanyi, R. E. Quality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodes J. Solid State Electrochem. 2009, 13, 51– 68 DOI: 10.1007/s10008-008-0608-1Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXht1Knu7zI&md5=953a27fe92b19acc3301ad2f9493c3bfQuality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodesLindner, Erno; Gyurcsanyi, Robert E.Journal of Solid State Electrochemistry (2009), 13 (1), 51-68CODEN: JSSEFS; ISSN:1432-8488. (Springer GmbH)A review. After a long history and conflicting views, solid-contact (SC) solvent polymeric membrane ion-selective electrodes (ISEs) emerged as reliable potentiometric-sensing devices with unique advantages. From the large variety of proposed SCs inherently conductive polymers emerged as the materials of choice. In the view, the most attractive feature of SC ISEs is their compatibility with thin- and thick-film micro-fabrication technologies that can provide cheap, mass-produced sensors and sensor arrays that can be integrated with the measuring, data acquisition, and control electronics in a straightforward way. However, despite the impressive properties of certain SC electrodes and their potential advantages, they remained primarily in the research labs. To make the jump from the research labs. into com. devices, it would be essential to prove that miniaturized SC ISEs can indeed match or surpass the performance characteristics of the conventional, liq.-contact macro-electrodes. It would be important to settle on the quality control criteria and testing protocols for assessing the performance characteristics of SC electrodes. It could help in interpreting the sometimes-inconsistent exptl. data. Once cheap, miniaturized, SC ISEs will match the performance characteristics of macroscopic-size electrodes, it is expected to have an important impact in a variety of applications requiring robust, maintenance-free, or single-use ISEs, e.g., in home care or bedside diagnostics, environmental anal., and quality control assessment. Reliable SC ISEs are expected to revitalize the field of ion-selective field effect transistors and open new possibilities in combination with nanowire-based devices.
- 23Qin, Y.; Peper, S.; Bakker, E. Plasticizer-free polymer membrane ion-selective electrodes containing a methacrylic copolymer matrix Electroanalysis 2002, 14, 1375– 1381 DOI: 10.1002/1521-4109(200211)14:19/20<1375::AID-ELAN1375>3.0.CO;2-8Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptVymu7k%253D&md5=8484b4c3e11ee2f9110078ceb4e31f63Plasticizer-free polymer membrane ion-selective electrodes containing a methacrylic copolymer matrixQin, Yu; Peper, Shane; Bakker, EricElectroanalysis (2002), 14 (19-20), 1375-1381CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A Me methacrylate and decyl methacrylate (MMA-DMA) copolymer was used to fabricate plasticizer-free ion-selective membranes. The copolymer matrix showed good mech. properties, and can be solvent cast in complete analogy to traditional ISE membranes. The material was evaluated in ionophore-free cation and anion exchanger membranes as well as in ion-selective electrode membranes contg. five different neutral ionophores. The selectivity of Na (X) based copolymer membranes is superior when compared to corresponding membranes made from poly(vinyl chloride) plasticized with bis(2-ethylhexyl sebacate) (PVC-DOS) and other plasticizer free membranes. Other ionophore-based MMA-DMA membranes, with the exception of magnesium-selective systems, also showed excellent selectivity similar to the corresponding PVC-DOS membranes. This makes MMA-DMA a potentially superior choice over alternative membrane matrixes reported in the literature and a promising platform for the establishment of covalently immobilized membrane components.
- 24Chumbimuni-Torres, K. Y.; Rubinova, N.; Radu, A.; Kubota, L. T.; Bakker, E. Solid contact potentiometric sensors for trace level measurements Anal. Chem. 2006, 78, 1318– 1322 DOI: 10.1021/ac050749yGoogle Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XitVGjsA%253D%253D&md5=1d812121c7c565c82fe79b014107823bSolid Contact Potentiometric Sensors for Trace Level MeasurementsChumbimuni-Torres, Karin Y.; Rubinova, Nastassia; Radu, Aleksandar; Kubota, Lauro T.; Bakker, EricAnalytical Chemistry (2006), 78 (4), 1318-1322CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A simple procedure for the development of a range of polymeric ion-selective electrodes (ISEs) with low detection limits is presented. The electrodes were prepd. by using a plasticizer-free Me methacrylate-decyl methacrylate copolymer as membrane matrix and poly(3-octylthiophene) as intermediate layer deposited by solvent casting on Au sputtered Cu electrodes as a solid inner contact. Five different electrodes were developed for Ag+, Pb2+, Ca2+, K+, and I-, with detection limits mostly in the nanomolar range. The lowest detection limits reported thus far with solid contact ISEs for the detection of Ag (2.0 × 10-9 M), K (10-7 M), and iodide (10-8 M) are presented. The developed electrodes exhibited a good response time and excellent reproducibility.
- 25Heng, L. Y.; Toth, K.; Hall, E. A. H. Ion-transport and diffusion coefficients of non-plasticised methacrylic-acrylic ion-selective membranes Talanta 2004, 63, 73– 87 DOI: 10.1016/j.talanta.2003.12.051Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXjt1yltrg%253D&md5=e68a31d8df876b7a791007e785d843e2Ion-transport and diffusion coefficients of non-plasticized methacrylic-acrylic ion-selective membranesHeng, Lee Yook; Toth, Klara; Hall, Elizabeth A. H.Talanta (2004), 63 (1), 73-87CODEN: TLNTA2; ISSN:0039-9140. (Elsevier Science B.V.)The ion-transport behavior of methacrylic-acrylic-based polymers for ion-selective electrode (ISE) membranes was studied by a spectrophotometric method to det. the apparent diffusion coeff. By observing the degree of deprotonation of the chromoionophore or chromogenic ionophore, the extent of penetration of cations into the polymer films was detd. The transport of the cations into the optode films depended on the stoichiometry of complexation by the ionophores. The apparent diffusion coeffs., estd. from the deprotonation data were of the order of 10-12 to 10-11 cm2 s-1. These values indicate that the apparent ion mobility in the methacrylic-acrylic ISE membranes is approx. a thousand times lower than that in plasticized PVC ISE membranes. For some ionophores, the value of the apparent diffusion coeff. could be modulated according to the ionophore content in the membrane and the data obtained for a calixarene contg. membrane were tested against a model for facilitated diffusion with chained carriers. The data did not fit a model where intramol. diffusion was limiting, but were consistent with a 1st-order rate-limiting mechanism involving an intermediate 1:2 complex between ion and ionophore. In this instance, the lowest values for Dapp were thus not necessarily obtained for lowest ionophore loading and in the range examd., a trend of decreasing Dapp with increasing ionophore was noted.
- 26Bakker, E.; Pretsch, E.; Buhlmann, P. Selectivity of potentiometric ion sensors Anal. Chem. 2000, 72, 1127– 1133 DOI: 10.1021/ac991146nGoogle Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXpsVKltg%253D%253D&md5=7e76604208bb1cee805e6205c80803a4Selectivity of Potentiometric Ion SensorsBakker, Eric; Pretsch, Ernoe; Buehlmann, PhilippeAnalytical Chemistry (2000), 72 (6), 1127-1133CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A review, with 29 refs., is given. Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quant. related to equil. at the interface between the sample and the electrode membrane. However, only correctly detd. selectivity coeffs. allow accurate predictions of ISE responses to real-world samples. also, they are also required for the optimization of ionophore structures and membrane compns. Best suited for such purposes are potentiometric selectivity coeffs. as defined already in the 1960s. This paper briefly reviews the basic relations and focuses on possible biases in the detn. of selectivity coeffs. The traditional methods to det. selectivity coeffs. (sep. soln. method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For example, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coeffs. may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to det. correct potentiometric selectivity coeffs. unaffected by such biases is presented.
- 27Hartung, J. Statistik: Lehr- und Handbuch der angewandten Statistik; R. Oldenbourg Verlag: Munich, 1989.Google ScholarThere is no corresponding record for this reference.
- 28Abril, G.; Bouillon, S.; Darchambeau, F.; Teodoru, C. R.; Marwick, T. R.; Tamooh, F.; Ochieng Omengo, F.; Geeraert, N.; Deirmendjian, L.; Polsenaere, P.; Borges, A. V. Technical Note: Large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters Biogeosciences 2015, 12, 67– 78 DOI: 10.5194/bg-12-67-2015Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVantrfL&md5=4c83158f0b16066b94207f84aa02ad48Technical note: large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwatersAbril, G.; Bouillon, S.; Darchambeau, F.; Teodoru, C. R.; Marwick, T. R.; Tamooh, F.; Omengo, F. Ochieng; Geeraert, N.; Deirmendjian, L.; Polsenaere, P.; Borges, A. V.Biogeosciences (2015), 12 (1), 67-78CODEN: BIOGGR; ISSN:1726-4189. (Copernicus Publications)Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atm. at the global scale. Fluxes of CO2 between aquatic systems and the atm. are calcd. from the gas transfer velocity and the water-air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calcd. from temp., pH and total alky. (TA). Here, we compare calcd. (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L-1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved org. carbon (DOC) (29 to 3970 μmol L-1). Calcd. pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calcd. pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most org.-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calcd. pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of org. acids anions to TA in waters with low carbonate alky. and high DOC concns.; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calcd. pCO2 to TA in acidic and organicrich waters. No empirical relationship could be derived from our data set in order to correct calcd. pCO2 for this bias. Owing to the widespread distribution of acidic, org.-rich freshwaters, we conclude that regional and global ests. of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quant. anal. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.
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- Gastón A. Crespo. Recent Advances in Ion-selective membrane electrodes for in situ environmental water analysis. Electrochimica Acta 2017, 245 , 1023-1034. https://doi.org/10.1016/j.electacta.2017.05.159
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Abstract
Figure 1
Figure 1. In situ profiles of dissolved oxygen, temperature, and total sulfide in July 2015 obtained simultaneously with the SC-ISE measurements in Lake Rotsee (A) and recorded by SC-ISEs to compare the performance of POT-based (red) and f-MWCNT-based (gray) ammonium sensors under dark conditions, where black circles represent ammonium concentrations in syringe samples taken simultaneously during the in situ profiling (B).
Figure 2
Figure 2. In situ profiles of dissolved oxygen concentration, temperature, and total sulfide in September 2015 obtained simultaneously with the SC-ISE measurements in Lake Rotsee (A) and recorded by SC-ISEs to extend the application to pH (green) measurements in addition to ammonium (gray) with f-MWCNT-based SC-ISEs in intense daylight, where black circles represent ammonium concentrations and green diamonds represent pH measurements in syringe samples taken simultaneously during the in situ profiling (B).
References
This article references 28 other publications.
- 1Kirf, M.; Røy, H.; Holtappels, M.; Fischer, J.; Schubert, C.; Wehrli, B. Redox gradients at the low oxygen boundary of lakes Aquat. Sci. 2015, 77, 81– 93 DOI: 10.1007/s00027-014-0365-41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1WrtLvE&md5=9dfb30d74715336c158d799a74f9f8b6Redox gradients at the low oxygen boundary of lakesKirf, Mathias K.; Roey, Hans; Holtappels, Moritz; Fischer, Jan P.; Schubert, Carsten J.; Wehrli, BernhardAquatic Sciences (2015), 77 (1), 81-93CODEN: AQSCEA; ISSN:1015-1621. (Birkhaeuser Basel)The distribution of oxygen (O2) at the oxic/anoxic interface in the water column of two Swiss lakes was measured with sub-micromolar sensitivity, high precision, and high spatial resoln. The O2 distribution was found to be highly variable and it is shown that N-cycling and the redox gradients of Mn, Fe and CH4 are controlled by O2 distributions down to the nanomolar concn. range. The profiles reveal that apparent gaps between the oxic zone and the sites of CH4 and Mn oxidn. are bridged by zones with 0.01-1 μmol L-1 O2 concns. and thus CH4 and Mn oxidn. clearly occur at oxic conditions. Directly below the steep oxycline of Lake Rot a broad low O2 zone in the depth range of 6-7.5 m was now detectable. The O2 increase during daylight in this zone was comparable to the O2 flux along the oxycline. Here photosynthesis could be responsible for a substantial part of the chemotrophic oxidn. processes. An even broader zone (0.8-3.8 m) with sub-micromolar O2 and evidence for methanotrophic and lithotrophic activities found at 160 m depth in the deep, dark hypolimnion of Lake Zug was maintained by transport, reaction- and mixing processes. The submicromolar zones could not have been resolved with traditional CTD-profiles. Their existence expands the oxic zone downwards and implies that substantial parts of "suboxic zones" characterized by the absence of both O2 and H2S may actually belong to the realm of oxic processes if more sensitive measurement techniques are used for their characterization.
- 2Durham, W. M.; Stocker, R. Thin Phytoplankton Layers: Characteristics, Mechanisms, and Consequences Annu. Rev. Mar. Sci. 2012, 4, 177– 207 DOI: 10.1146/annurev-marine-120710-1009572https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC38rgsFamsg%253D%253D&md5=4c00272deba88c04debbbf19d2561c10Thin phytoplankton layers: characteristics, mechanisms, and consequencesDurham William M; Stocker RomanAnnual review of marine science (2012), 4 (), 177-207 ISSN:1941-1405.For over four decades, aggregations of phytoplankton known as thin layers have been observed to harbor large amounts of photosynthetic cells within narrow horizontal bands. Field observations have revealed complex linkages among thin phytoplankton layers, the physical environment, cell behavior, and higher trophic levels. Several mechanisms have been proposed to explain layer formation and persistence, in the face of the homogenizing effect of turbulent dispersion. The challenge ahead is to connect mechanistic hypotheses with field observations to gain better insight on the phenomena that shape layer dynamics. Only through a mechanistic understanding of the relevant biological and physical processes can we begin to predict the effect of thin layers on the ecology of phytoplankton and higher organisms.
- 3Athavale, R.; Kokorite, I.; Dinkel, C.; Bakker, E.; Wehrli, B.; Crespo, G. A.; Brand, A. In Situ Ammonium Profiling Using Solid-Contact Ion-Selective Electrodes in Eutrophic Lakes Anal. Chem. 2015, 87, 11990– 11997 DOI: 10.1021/acs.analchem.5b024243https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVGhs7vJ&md5=f45a56ee9162b8e04bddf8fd2018baa4In Situ Ammonium Profiling Using Solid-Contact Ion-Selective Electrodes in Eutrophic LakesAthavale, Rohini; Kokorite, Ilga; Dinkel, Christian; Bakker, Eric; Wehrli, Bernhard; Crespo, Gaston A.; Brand, AndreasAnalytical Chemistry (Washington, DC, United States) (2015), 87 (24), 11990-11997CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A promising profiling setup for in situ measurements in lakes with potentiometric solid-contact ion-selective electrodes (SC-ISEs) and a data processing method for sensor calibration and drift correction are presented. The profiling setup consists of a logging system, which is equipped with a syringe sampler and sensors for the measurement of std. parameters including temp., cond., O and photosynthetically active radiation (PAR). The setup was expanded with SC-ISEs in galvanically sepd. amplifiers. The potential for high-resoln. profiling is studied by deploying the setup in the eutrophic Lake Rotsee (Lucerne, Switzerland), using 2 different designs of ammonium sensing SC-ISEs. Ammonium was chosen as a target analyte, since it is the most common reduced inorg. N species involved in various pathways of the N cycle and is therefore indicative of numerous biogeochem. processes that occur in lakes such as denitrification and primary prodn. One of the designs, which uses a composite C-nanotube-PVC-based membrane, suffered from sulfide poisoning in the deeper, sulfidic regions of the lake. In contrast, electrodes contg. a plasticizer-free methacrylate copolymer-based sensing layer on top of a conducting polymer layer as a transducer did not show this poisoning effect. The syringe samples drawn during continuous profiling were utilized to calibrate the electrode response. Reaction hotspots and steep gradients of ammonium concns. were identified on-site by monitoring the electrode potential online. Upon conversion to high-resoln. concn. profiles, fine scale features between the calibration points were displayed, which would have been missed by conventional limnol. sampling and subsequent lab. analyses. Thus, the presented setup with SC-ISEs tuned to analytes of interest can facilitate the study of biogeochem. processes that occur at the centimeter scale.
- 4Sutter, J.; Radu, A.; Peper, S.; Bakker, E.; Pretsch, E. Solid-contact polymeric membrane electrodes with detection limits in the subnanomolar range Anal. Chim. Acta 2004, 523, 53– 59 DOI: 10.1016/j.aca.2004.07.0164https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXnsVGgsb4%253D&md5=e1089328f8878a87ff653e2c1ebb4acaSolid-contact polymeric membrane electrodes with detection limits in the subnanomolar rangeSutter, Jolanda; Radu, Aleksandar; Peper, Shane; Bakker, Eric; Pretsch, ErnoeAnalytica Chimica Acta (2004), 523 (1), 53-59CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)Ion-selective electrode (ISE) membranes with a solid contact rather than a traditional liq. inner contact are anticipated to give lower detection limits because of diminished ion fluxes. Often, however, ill-defined solid contacts give rise to instabilities and interferences by O gas. Here, a poly(Me methacrylate)/poly(decyl methacrylate) (MMA/DMA) copolymer as membrane matrix was solvent-cast on a layer of poly(n-octyl)thiophene (POT) deposited on Au as internal contact. The resulting Ca2+- and Pb2+-selective electrodes were not sensitive to O2 and no evidence was found for the presence of a H2O film between membrane and internal contact. However, a H2O film was present when electropolymd. poly(n-octyl)thiophene was used. In the absence of a conducting polymer, O2 induced a significant change in the EMF but no clear evidence was found for a H2O film between POT and the MMA/DMA membrane. The lower detection limit of the new Au-POT-MMA/DMA solid-contact electrodes was somewhat better than that obsd. with a corresponding liq.-contact ISE and reached subnanomolar levels. Importantly, the response times for the solid-contact ISE are, at low concns., much faster than for the liq.-contact ISE.
- 5Crespo, G. A.; Macho, S.; Rius, F. X. Ion-selective electrodes using carbon nanotubes as ion-to-electron transducers Anal. Chem. 2008, 80, 1316– 1322 DOI: 10.1021/ac071156l5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsl2msA%253D%253D&md5=fb603684e62e06f6150085731e77f225Ion-Selective Electrodes Using Carbon Nanotubes as Ion-to-Electron TransducersCrespo, Gaston A.; Macho, Santiago; Rius, F. XavierAnalytical Chemistry (Washington, DC, United States) (2008), 80 (4), 1316-1322CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)This study developed a new type of all-solid-state ion-selective electrode based on a transducing layer of a network of single-walled C nanotubes. The extraordinary capacity of C nanotubes to promote electron transfer between heterogeneous phases made the presence of electroactive polymers or any other ion-to-electron-transfer promoter unnecessary. The new transducer layer was characterized by environmental SEM and electrochem. impedance spectroscopy. The stability of the elec. potential of the new solid-contact electrode was examd. by performing current-reversal chronopotentiometry, and the influence of the interfacial H2O film was assessed by the potentiometric H2O layer test. The performance of the new electrode was evaluated by detg. K+ with an ion-selective membrane that contained the known valinomycin ion carrier. The new electrode had a Nernstian slope (58.4 mV/decade), dynamic ranges of four logarithmic units, and selectivities and limits of detection comparable to other solid-contact electrodes. The short response time (<10 s for activities >10-5.5 M) and the stability of the signal over several days makes these new electrodes very promising candidates for attaining true miniaturization.
- 6Bobacka, J.; Ivaska, A.; Lewenstam, A. Potentiometric ion sensors Chem. Rev. 2008, 108, 329– 351 DOI: 10.1021/cr068100w6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsl2qtA%253D%253D&md5=5bbaa0cbb71586bdbf5d93a140f4d743Potentiometric Ion SensorsBobacka, Johan; Ivaska, Ari; Lewenstam, AndrzejChemical Reviews (Washington, DC, United States) (2008), 108 (2), 329-351CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The aim of this review is to highlight some of these modern topics in the field of potentiometric ion sensors. This review is focused on recent achievements since the beginning of this millennium and emphasizes the results from the last 5 years (2002-2006). Section 2 gives a crit. overview, placed in a historical perspective, on the theory of the potentiometric response, including classical equil. models as well as advanced nonequil. models. Section 3 deals with recent advances in the field of solid-contact ion-selective electrodes (ISEs), emphasizing the application of conducting polymers as ion-to-electron transducers. Recent developments in the area of miniaturized ISEs, including applications in flow anal., life science, and biol., are discussed in section 4. Finally, the new wave of ISEs is commented on in section 5. The authors hope that the issues discussed will illustrate the great possibilities offered by modern ISEs and encourage further innovations in the rapidly expanding field of chem. sensors in the years to come.
- 7Bakker, E.; Pretsch, E. Modern Potentiometry Angew. Chem., Int. Ed. 2007, 46, 5660– 5668 DOI: 10.1002/anie.2006050687https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXosFOkt7Y%253D&md5=36afcaafe768381e76bcc13983cbfd91Modern potentiometryBakker, Eric; Pretsch, ErnoeAngewandte Chemie, International Edition (2007), 46 (30), 5660-5668CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. A silent revolution of ion-selective electrodes (ISEs) took place during the past decade. Polymeric membrane electrodes are now routinely used to det. complex formation consts. between lipophilic guests and ionic hosts. Ultratrace level measurements have become possible even in samples of very small vols., with detection limits in the attomole range.
- 8Yuan, D.; Anthis, A. H. C.; Ghahraman Afshar, M.; Pankratova, N.; Cuartero, M.; Crespo, G. A.; Bakker, E. All-Solid-State Potentiometric Sensors with a Multiwalled Carbon Nanotube Inner Transducing Layer for Anion Detection in Environmental Samples Anal. Chem. 2015, 87, 8640– 8645 DOI: 10.1021/acs.analchem.5b019418https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlemurjO&md5=e0484a7b9d636d491402bcfb9953cd7cAll-Solid-State Potentiometric Sensors with a Multiwalled Carbon Nanotube Inner Transducing Layer for Anion Detection in Environmental SamplesYuan, Dajing; Anthis, Alexandre H. C.; Ghahraman Afshar, Majid; Pankratova, Nadezda; Cuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2015), 87 (17), 8640-8645CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)While ion to electron transducing layers for the fabrication of potentiometric membrane electrodes for the detection of cations were well established, similar progress for the sensing of anions has not yet been realized. The authors report for this reason on a novel approach for the development of all-solid-state anion selective electrodes using lipophilic multiwalled carbon nanotubes (f-MWCNTs) as the inner ion to electron transducing layer. This material can be solvent cast, as it conveniently dissolves in THF, an important advantage to develop uniform films without the need for using surfactants that might deteriorate the performance of the electrode. Solid contact sensors for carbonate, nitrate, nitrite, and dihydrogen phosphate are fabricated and characterized, and all exhibit comparable anal. characteristics to the inner liq. electrodes. For example, the carbonate sensor exhibits a Nernstian slope of 27.2 ± 0.8 mV dec-1, a LOD = 2.3 μM, a response time of 1 s, a linear range of four logarithmic units, and a medium-term stability of 0.04 mV h-1 was obtained in a pH 8.6 buffered soln. Water layer test, reversibility, and selectivity for chloride, nitrate, and hydroxide are also reported. The excellent properties of f-MWCNTs as a transducer are contrasted to the deficient performance of poly(3-octyl-thiophene) (POT) for carbonate detection. This is evidenced both with a significant drift in the potentiometric measures as well as a pronounced sensitivity to light (either sunlight or artificial light). This latter aspect may compromise its potential for environmental in situ measurements (night/day cycles). The concn. of carbonate is detd. in a river sample (Arve river, Geneva) and compared to a ref. method (automatic titrator with potentiometric pH detection). Probably nanostructured materials such as f-MWCNTs are an attractive platform as a general ion-to-electron transducer for anion-selective electrodes.
- 9Crespo, G. A.; Macho, S.; Bobacka, J.; Rius, F. X. Transduction Mechanism of Carbon Nanotubes in Solid-Contact Ion-Selective Electrodes Anal. Chem. 2009, 81, 676– 681 DOI: 10.1021/ac802078z9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsFaisrbP&md5=f3b68e74effcda6758f972a78902c5edTransduction Mechanism of Carbon Nanotubes in Solid-Contact Ion-Selective ElectrodesCrespo, Gaston A.; Macho, Santiago; Bobacka, Johan; Rius, F. XavierAnalytical Chemistry (Washington, DC, United States) (2009), 81 (2), 676-681CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Porous carbon materials and carbon nanotubes were recently used as solid contacts in ion-selective electrodes (ISE), and the signal transduction mechanism of these carbon-based materials is therefore of great interest. The ion-to-electron transduction mechanism of carbon nanotubes is studied by using electrochem. impedance spectroscopy (EIS) and cyclic voltammetry (CV). Single-walled carbon nanotubes (SWCNT) are deposited on glassy carbon (GC) disk electrodes by repetitive spraying, resulting in SWCNT layers with thicknesses of 10, 35, and 50 μm. The impedance spectra of these GC/SWCNT electrodes in contact with aq. electrolyte soln. show a very small resistance and a large bulk capacitance that is related to a large effective double layer at the SWCNT/electrolyte interface. The impedance response of GC/SWCNT is very similar to that of poly(3,4-ethylenedioxythiophene) (PEDOT) film electrodes studied earlier under the same exptl. conditions. The same equiv. circuit is valid for both types of materials. The reason is that both materials can be described schematically as an asym. capacitor where one side is formed by electronic charge (electrons/holes) in the SWCNT wall or along the conjugated polymer chain of PEDOT and the other side is formed by ions (anions/cations) in the soln. (or in the ion-selective membrane when used as a solid contact in ISE).
- 10Dumitrescu, I.; Unwin, P. R.; Macpherson, J. V. Electrochemistry at carbon nanotubes: perspective and issues Chem. Commun. 2009, 6886– 6901 DOI: 10.1039/b909734a10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtl2iurfF&md5=e9b6c4c9efad4f443ef5edbdb383b795Electrochemistry at carbon nanotubes: perspective and issuesDumitrescu, Ioana; Unwin, Patrick R.; MacPherson, Julie V.Chemical Communications (Cambridge, United Kingdom) (2009), (45), 6886-6901CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A review. Electrochem. at C nanotubes (CNTs) is a large and growing field, but one in which there is still uncertainty about the fundamental activity of CNTs as electrode materials. On the one hand, there are many reports which focus on the favorable electrochem. properties of CNT electrodes, such as enhanced detection sensitivity, electrocatalytic effects and reduced fouling. However, other studies suggest that CNTs may be no more electroactive than graphitic powder. Also, probably the catalytic nanoparticles from which CNTs are formed may dominate the electrochem. characteristics in some instances. A considerable body of the literature presumes that the CNT sidewall is inert and that edge-plane-graphite-like open ends and defect sites are responsible for the electron transfer activity obsd. But studies of well characterized single-walled nanotube (SWNT) electrodes, either as individual tubes or as 2-dimensional networks, suggest sidewall activity. This review highlights how the various discrepancies in CNT electrochem. may have arisen, by taking a historical view of the field and identifying crucial issues that still need to be solved. When assessing the behavior of CNT electrodes, it is vitally important that careful consideration is given to CNT used (SWNT or multi-walled), the quality of (presence of impurities), the effect of chem. processing steps in the fabrication of electrodes and the exptl. arrangements adopted. Understanding these key features is an essential requirement to develop a fundamental understanding of CNT electrochem., to allow a wide range of electroanal. applications, and to move the field forward rationally. As part of this process, high resoln. electrochem. and elec. imaging techniques are expected to play a significant role in the future, as well as theor. developments which examine the fundamentals of electron transfer at different types of CNTs and their characteristic surface sites.
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- 14Crespo, G. A.; Gugsa, D.; Macho, S.; Rius, F. X. Solid-contact pH-selective electrode using multi-walled carbon nanotubes Anal. Bioanal. Chem. 2009, 395, 2371– 2376 DOI: 10.1007/s00216-009-3127-814https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFCnsrbN&md5=1640f851ca344ced4991fb8b25a47c3eSolid-contact pH-selective electrode using multi-walled carbon nanotubesCrespo, Gaston A.; Gugsa, Derese; Macho, Santiago; Rius, F. XavierAnalytical and Bioanalytical Chemistry (2009), 395 (7), 2371-2376CODEN: ABCNBP; ISSN:1618-2642. (Springer)Multi-walled C nanotubes (MWCNT) are efficient transducers of the ionic-to-electronic current. This enables the development of a new solid-contact pH-selective electrode that is based on the deposition of a 35-μm thick layer of MWCNT between the acrylic ion-selective membrane and the glassy C rod used as the elec. conductor. The ion-selective membrane was prepd. by incorporating tridodecylamine as the ionophore, K tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as the lipophilic additive in a polymd. methylmethacrylate and an Bu acrylate matrix. The potentiometric response shows Nernstian behavior and a linear dynamic range between 2.89 and 9.90 pH values. The response time for this electrode was <10 s throughout the whole working range. The electrode shows a high selectivity towards interfering ions. Electrochem. impedance spectroscopy and chronopotentiometry techniques were used to characterize the electrochem. behavior and the stability of the C-nanotube-based ion-selective electrodes.
- 15Maksymiuk, K. Chemical Reactivity of Polypyrrole and Its Relevance to Polypyrrole Based Electrochemical Sensors Electroanalysis 2006, 18, 1537– 1551 DOI: 10.1002/elan.200603573There is no corresponding record for this reference.
- 16Brand, A.; Bruderer, H.; Oswald, K.; Guggenheim, C.; Schubert, C. J.; Wehrli, B. Oxygenic primary production below the oxycline and its importance for redox dynamics Aquat. Sci. 2016, 78, 727– 741 DOI: 10.1007/s00027-016-0465-416https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVOntrc%253D&md5=523289ceef04015d613a2cb46964de51Oxygenic primary production below the oxycline and its importance for redox dynamicsBrand, Andreas; Bruderer, Hannah; Oswald, Kirsten; Guggenheim, Carole; Schubert, Carsten J.; Wehrli, BernhardAquatic Sciences (2016), 78 (4), 727-741CODEN: AQSCEA; ISSN:1015-1621. (Birkhaeuser Basel)We present evidence that oxygenic primary prodn. occurs in the virtually anoxic regions (i.e. regions where no oxygen was detected) of the eutrophic, pre-alpine Lake Rot (Switzerland). Chlorophyll-a measurements in combination with phytoplankton densities indicated the presence of oxygenic primary producers throughout the water column. While Chlorophyceae were present as the main class of oxygenic phototrophs above the oxycline, which extended from 8 down to 9.2 m, the phototrophic community in and below the oxycline was dominated by cyanobacteria. In-situ incubation expts. with H14CO3- conducted in August 2013 revealed an oxygenic primary prodn. rate of 1.0 and 0.5 mg C m-3 h-1 in 9 and 10 m depth, resp. However, measurements with optical trace oxygen sensors showed that oxygen concns. were below the detection limit (20 nmol l-1) during the incubation period below 9.2 m. Potential oxygen consumption rates, which were 10-20 times higher than oxygen prodn. rates, explain this absence of free oxygen. Our data show that oxygen prodn. in the virtually anoxic zone corresponded to approx. 8 % of the oxygen flux driven by the concn. gradient in the oxycline. This provided an important source of electron acceptors for biogeochem. processes beyond the conventional redox boundary and in the apparently oxygen depleted zone of Lake Rot. This oxygenic primary prodn. in the virtually anoxic zone could allow growth and activity of aerobic microorganisms adapted to low oxygen supply.
- 17Parsons, T. R.; Maita, Y.; Lalli, C. M. A manual of chemical and biological methods for seawater analysis; Pergamon Press: Oxford, U.K., 1984.There is no corresponding record for this reference.
- 18Cline, J. D. Spectrophotometric determination of hydrogen sulfide in natural waters Limnol. Oceanogr. 1969, 14, 454– 458 DOI: 10.4319/lo.1969.14.3.045418https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1MXksFegu70%253D&md5=d7e10415590a7dd4dc2e1c4c3896a0dbSpectrophotometric determination of hydrogen sulfide in natural watersCline, Joel D.Limnology and Oceanography (1969), 14 (3), 454-8CODEN: LIOCAH; ISSN:0024-3590.To det. dissolved H2S (H2S, HS-, S2-) in the concn. range of 1-1,000 μg./l., a mixed diamine reagent is used which is prepd. by dissolving 0.5-20 g. (depending on sulfide concn.) of N,N-dimethyl-p-phenylenediamine sulfate and FeCl3.6H2O (0.75-30.0 g. depending on sulfide concn.) in 500 ml. of cool 50% reagent grade HCl. In sulfide concn. in μmoles/l. is 1-3, the amt. of diamine is 0.5 g. and the Fe(III) is 0.75 g.; at 3-40, the diamine is 2.0 and Fe is 3.0; at 40-250 diamine is 8.0 and Fe is 12.0; at 250-1000 the diamine level is 20.0 and the Fe is 30.0. Exptl. a 50-ml. sample is transferred from the syringe to a 50-ml. serum bottle, to which 4 ml. of the appropriate mixed diamine reagent is added. A 5-ml. syringe with a 4-ml. stop position is satisfactory for reagent delivery. The serum cap is replaced promptly to reduce volatilization of the H2S and the soln. is mixed gently. After 20 min. the absorbance is detd. spectrophotometrically at 670 mμ in the appropriate cuvette. All necessary dilns. should be made after the color development time and in volumetric glassware. Diln. factors and path lengths are recommended for best results. Standardization is described and sensitivity, precision, and accuracy are detd. Temp. effect and interferences are discussed.
- 19Lindner, E.; Toth, K.; Pungor, E. Definition and determination of response time of ion selective electrodes Pure Appl. Chem. 1986, 58, 469– 479 DOI: 10.1351/pac198658030469There is no corresponding record for this reference.
- 20DeMarco, R.; Clarke, G.; Pejcic, B. Ion-Selective Electrode Potentiometry in Environmental Analysis Electroanalysis 2007, 19, 1987– 2001 DOI: 10.1002/elan.200703916There is no corresponding record for this reference.
- 21Kharissova, O. V.; Kharisov, B. I.; de Casas Ortiz, E. G. Dispersion of carbon nanotubes in water and non-aqueous solvents RSC Adv. 2013, 3, 24812– 24852 DOI: 10.1039/c3ra43852j21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslCrs7fO&md5=9123dcbc01cfba4bc3775379cf85e7d1Dispersion of carbon nanotubes in water and non-aqueous solventsKharissova, Oxana V.; Kharisov, Boris I.; de Casas Ortiz, Edgar GerardoRSC Advances (2013), 3 (47), 24812-24852CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)A review. Contemporary methods for dispersion of carbon nanotubes in water and non-aq. media are discussed. Most attention is paid to ultrasonic and plasma techniques and other phys. techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and org. salts, mineral and org. acids, oxides, inorg. and org. peroxides, org. sulfonates, polymers, dyes, natural products, biomols., and coordination compds.). Special studies on CNTs solubilization are examd.
- 22Lindner, E.; Gyurcsanyi, R. E. Quality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodes J. Solid State Electrochem. 2009, 13, 51– 68 DOI: 10.1007/s10008-008-0608-122https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXht1Knu7zI&md5=953a27fe92b19acc3301ad2f9493c3bfQuality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodesLindner, Erno; Gyurcsanyi, Robert E.Journal of Solid State Electrochemistry (2009), 13 (1), 51-68CODEN: JSSEFS; ISSN:1432-8488. (Springer GmbH)A review. After a long history and conflicting views, solid-contact (SC) solvent polymeric membrane ion-selective electrodes (ISEs) emerged as reliable potentiometric-sensing devices with unique advantages. From the large variety of proposed SCs inherently conductive polymers emerged as the materials of choice. In the view, the most attractive feature of SC ISEs is their compatibility with thin- and thick-film micro-fabrication technologies that can provide cheap, mass-produced sensors and sensor arrays that can be integrated with the measuring, data acquisition, and control electronics in a straightforward way. However, despite the impressive properties of certain SC electrodes and their potential advantages, they remained primarily in the research labs. To make the jump from the research labs. into com. devices, it would be essential to prove that miniaturized SC ISEs can indeed match or surpass the performance characteristics of the conventional, liq.-contact macro-electrodes. It would be important to settle on the quality control criteria and testing protocols for assessing the performance characteristics of SC electrodes. It could help in interpreting the sometimes-inconsistent exptl. data. Once cheap, miniaturized, SC ISEs will match the performance characteristics of macroscopic-size electrodes, it is expected to have an important impact in a variety of applications requiring robust, maintenance-free, or single-use ISEs, e.g., in home care or bedside diagnostics, environmental anal., and quality control assessment. Reliable SC ISEs are expected to revitalize the field of ion-selective field effect transistors and open new possibilities in combination with nanowire-based devices.
- 23Qin, Y.; Peper, S.; Bakker, E. Plasticizer-free polymer membrane ion-selective electrodes containing a methacrylic copolymer matrix Electroanalysis 2002, 14, 1375– 1381 DOI: 10.1002/1521-4109(200211)14:19/20<1375::AID-ELAN1375>3.0.CO;2-823https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptVymu7k%253D&md5=8484b4c3e11ee2f9110078ceb4e31f63Plasticizer-free polymer membrane ion-selective electrodes containing a methacrylic copolymer matrixQin, Yu; Peper, Shane; Bakker, EricElectroanalysis (2002), 14 (19-20), 1375-1381CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)A Me methacrylate and decyl methacrylate (MMA-DMA) copolymer was used to fabricate plasticizer-free ion-selective membranes. The copolymer matrix showed good mech. properties, and can be solvent cast in complete analogy to traditional ISE membranes. The material was evaluated in ionophore-free cation and anion exchanger membranes as well as in ion-selective electrode membranes contg. five different neutral ionophores. The selectivity of Na (X) based copolymer membranes is superior when compared to corresponding membranes made from poly(vinyl chloride) plasticized with bis(2-ethylhexyl sebacate) (PVC-DOS) and other plasticizer free membranes. Other ionophore-based MMA-DMA membranes, with the exception of magnesium-selective systems, also showed excellent selectivity similar to the corresponding PVC-DOS membranes. This makes MMA-DMA a potentially superior choice over alternative membrane matrixes reported in the literature and a promising platform for the establishment of covalently immobilized membrane components.
- 24Chumbimuni-Torres, K. Y.; Rubinova, N.; Radu, A.; Kubota, L. T.; Bakker, E. Solid contact potentiometric sensors for trace level measurements Anal. Chem. 2006, 78, 1318– 1322 DOI: 10.1021/ac050749y24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XitVGjsA%253D%253D&md5=1d812121c7c565c82fe79b014107823bSolid Contact Potentiometric Sensors for Trace Level MeasurementsChumbimuni-Torres, Karin Y.; Rubinova, Nastassia; Radu, Aleksandar; Kubota, Lauro T.; Bakker, EricAnalytical Chemistry (2006), 78 (4), 1318-1322CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A simple procedure for the development of a range of polymeric ion-selective electrodes (ISEs) with low detection limits is presented. The electrodes were prepd. by using a plasticizer-free Me methacrylate-decyl methacrylate copolymer as membrane matrix and poly(3-octylthiophene) as intermediate layer deposited by solvent casting on Au sputtered Cu electrodes as a solid inner contact. Five different electrodes were developed for Ag+, Pb2+, Ca2+, K+, and I-, with detection limits mostly in the nanomolar range. The lowest detection limits reported thus far with solid contact ISEs for the detection of Ag (2.0 × 10-9 M), K (10-7 M), and iodide (10-8 M) are presented. The developed electrodes exhibited a good response time and excellent reproducibility.
- 25Heng, L. Y.; Toth, K.; Hall, E. A. H. Ion-transport and diffusion coefficients of non-plasticised methacrylic-acrylic ion-selective membranes Talanta 2004, 63, 73– 87 DOI: 10.1016/j.talanta.2003.12.05125https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXjt1yltrg%253D&md5=e68a31d8df876b7a791007e785d843e2Ion-transport and diffusion coefficients of non-plasticized methacrylic-acrylic ion-selective membranesHeng, Lee Yook; Toth, Klara; Hall, Elizabeth A. H.Talanta (2004), 63 (1), 73-87CODEN: TLNTA2; ISSN:0039-9140. (Elsevier Science B.V.)The ion-transport behavior of methacrylic-acrylic-based polymers for ion-selective electrode (ISE) membranes was studied by a spectrophotometric method to det. the apparent diffusion coeff. By observing the degree of deprotonation of the chromoionophore or chromogenic ionophore, the extent of penetration of cations into the polymer films was detd. The transport of the cations into the optode films depended on the stoichiometry of complexation by the ionophores. The apparent diffusion coeffs., estd. from the deprotonation data were of the order of 10-12 to 10-11 cm2 s-1. These values indicate that the apparent ion mobility in the methacrylic-acrylic ISE membranes is approx. a thousand times lower than that in plasticized PVC ISE membranes. For some ionophores, the value of the apparent diffusion coeff. could be modulated according to the ionophore content in the membrane and the data obtained for a calixarene contg. membrane were tested against a model for facilitated diffusion with chained carriers. The data did not fit a model where intramol. diffusion was limiting, but were consistent with a 1st-order rate-limiting mechanism involving an intermediate 1:2 complex between ion and ionophore. In this instance, the lowest values for Dapp were thus not necessarily obtained for lowest ionophore loading and in the range examd., a trend of decreasing Dapp with increasing ionophore was noted.
- 26Bakker, E.; Pretsch, E.; Buhlmann, P. Selectivity of potentiometric ion sensors Anal. Chem. 2000, 72, 1127– 1133 DOI: 10.1021/ac991146n26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXpsVKltg%253D%253D&md5=7e76604208bb1cee805e6205c80803a4Selectivity of Potentiometric Ion SensorsBakker, Eric; Pretsch, Ernoe; Buehlmann, PhilippeAnalytical Chemistry (2000), 72 (6), 1127-1133CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A review, with 29 refs., is given. Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quant. related to equil. at the interface between the sample and the electrode membrane. However, only correctly detd. selectivity coeffs. allow accurate predictions of ISE responses to real-world samples. also, they are also required for the optimization of ionophore structures and membrane compns. Best suited for such purposes are potentiometric selectivity coeffs. as defined already in the 1960s. This paper briefly reviews the basic relations and focuses on possible biases in the detn. of selectivity coeffs. The traditional methods to det. selectivity coeffs. (sep. soln. method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For example, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coeffs. may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to det. correct potentiometric selectivity coeffs. unaffected by such biases is presented.
- 27Hartung, J. Statistik: Lehr- und Handbuch der angewandten Statistik; R. Oldenbourg Verlag: Munich, 1989.There is no corresponding record for this reference.
- 28Abril, G.; Bouillon, S.; Darchambeau, F.; Teodoru, C. R.; Marwick, T. R.; Tamooh, F.; Ochieng Omengo, F.; Geeraert, N.; Deirmendjian, L.; Polsenaere, P.; Borges, A. V. Technical Note: Large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters Biogeosciences 2015, 12, 67– 78 DOI: 10.5194/bg-12-67-201528https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVantrfL&md5=4c83158f0b16066b94207f84aa02ad48Technical note: large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwatersAbril, G.; Bouillon, S.; Darchambeau, F.; Teodoru, C. R.; Marwick, T. R.; Tamooh, F.; Omengo, F. Ochieng; Geeraert, N.; Deirmendjian, L.; Polsenaere, P.; Borges, A. V.Biogeosciences (2015), 12 (1), 67-78CODEN: BIOGGR; ISSN:1726-4189. (Copernicus Publications)Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atm. at the global scale. Fluxes of CO2 between aquatic systems and the atm. are calcd. from the gas transfer velocity and the water-air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calcd. from temp., pH and total alky. (TA). Here, we compare calcd. (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L-1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved org. carbon (DOC) (29 to 3970 μmol L-1). Calcd. pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calcd. pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most org.-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calcd. pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of org. acids anions to TA in waters with low carbonate alky. and high DOC concns.; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calcd. pCO2 to TA in acidic and organicrich waters. No empirical relationship could be derived from our data set in order to correct calcd. pCO2 for this bias. Owing to the widespread distribution of acidic, org.-rich freshwaters, we conclude that regional and global ests. of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quant. anal. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.
Supporting Information
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.estlett.7b00130.
Experimental section with electrode fabrication, laboratory calibration (Figure S1), water-layer test (Figure S2), redox sensitivity test (Figure S3), uncertainty analysis (Figure S4), absolute error analysis (Figure S5), in situ profiling setup (Figure S6), in situ calibration parameters (Table S1), selectivity coefficients for ion selective membranes and mean concentrations of relevant ions in the lake water column (Table S2), and properties of SC-ISEs (Table S3) (PDF)
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