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Thin Layer Coulometry with Ionophore Based Ion-Selective Membranes
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Department of Chemistry, Nanochemistry Research Institute, Curtin University of Technology, Perth, WA 6845, Australia
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Analytical Chemistry

Cite this: Anal. Chem. 2010, 82, 11, 4537–4542
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https://doi.org/10.1021/ac100524z
Published April 29, 2010

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Abstract

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We are demonstrating here for the first time a thin layer coulometric detection mode for ionophore based liquid ion-selective membranes. Coulometry promises to achieve the design of robust, calibration free sensors that are especially attractive for applications where recalibration in situ is difficult or undesirable. This readout principle is here achieved with porous polypropylene tubing doped with the membrane material and which contains a chlorinated silver wire in the inner compartment, together with the fluidically delivered sample solution. The membrane material consists of the lipophilic plasticizer dodecyl 2-nitrophenyl ether, the lipophilic electrolyte ETH 500, and the calcium ionophore ETH 5234. Importantly and in contrast to earlier work on voltammetric liquid membrane electrodes, the membrane also contains a cation-exchanger salt, KTFPB. This renders the membrane permselective and allows one to observe open circuit potentiometric responses for the device, which is confirmed to follow the expected Nernstian equation. Moreover, as the same cationic species is now potential determining at both interfaces of the membrane, it is possible to use rapidly diffusing and/or thin membrane systems where transport processes at the inner and outer interface of the membrane do not perturb each other or the overall composition of the membrane. The tubing is immersed in an electrolyte solution where the counter and working electrode are placed, and the potentials are applied relative to the measured open circuit potentials. Exhaustive current decays are observed in the range of 10 to 100 μM calcium chloride. The observed charge, calculated as integrated currents, is linearly dependent on concentration and forms the basis for the coulometric readout of ion-selective membrane electrodes.

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Subjects

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Modern directions in chemical sensing demand the realization of self-contained, robust sensing principles that do not require frequent supervision or recalibration in the field. Environmental remote chemical sensing applications with a large network of inexpensive chemical sensors, for instance, would have tremendous promise in monitoring programs. Current technologies are often restricted to passive, nonselective optical systems. (1) While state of the art in electrochemical sensing technology may offer adequate selectivity and sensitivity in many cases, (2, 3) it still utilizes traditional transduction principles, including potentiometry and amperometry. These have never been intended for recalibration free and robust sensing approaches. In the clinical laboratory setting, for instance, where sensors based on such principles are employed in vast numbers, a one point recalibration step is typically performed with each sample reading to compensate for any drift in the sensor output signal. (4) Clearly, the transduction principles of electrochemical sensors must be reconsidered from fundamental principles to achieve the ambitious goals mentioned above. (5)
Absolute measurement principles in the analytical sciences are rare, but they do include gravimetry and coulometry. In controlled potential coulometry, the current associated with a specific redox reaction is monitored until it decays to near-zero values. (6) The observed current integrated over the time period gives the overall charge, which ideally relates to the number of moles of material converted in the sample using Faraday’s law. The use of thin layer samples, as in thin layer coulometry, improves the speed of analysis relative to the use of voluminous samples. (7) The key challenge in employing this readout principle for chemical sensors has been that redox reactions at metal electrodes tend not to be sufficiently selective. Recently, however, a coulometric readout was successfully used in enzymatic glucose bioassays, for example, allowing one to exploit the confined volume for the exhaustive electrolysis of potential interferences before the actual glucose assay. (8)
The electrochemical detection of ionic species is preferably accomplished with ion-selective electrodes. Polymeric or liquid membrane systems are now particularly well developed, and their sensing selectivities are a function of membrane extraction and complexation processes. (9, 10) These membranes are traditionally read out by zero current potentiometry, often giving extremely low detection limits. (11) Moreover, the use of voltammetric methods on membrane electrodes has increased in recent years, including cyclic voltammetry and amperometry, (12) stripping voltammetry, (13) normal pulse voltammetry, (14) and pulsed chronopotentiometry. (15, 16) When exploring these as sensor readout principles, the membrane was normally chosen not to exhibit ion-exchanger properties in order to achieve a sample−membrane interface that can be effectively polarized by the electrochemical perturbation step.
The groups of Sanchez-Pedreno (17) and Osakai (18) were reportedly the first to use ion transfer voltammetry principles in a flow system to demonstrate the coulometric detection of very lipophilic ions. These two early works did not yet utilize chemical receptors (ionophores), and the coulometric efficiency was not yet optimal. Kihara and co-workers offered the first description of small ion detection with ionophores with this approach, using a porous Teflon tubing that was wholly immersed into an organic solvent that contained a lipophilic electrolyte and a chemical receptor. (19) Kihara and co-workers indeed showed that the absolute detection of ionic species is possible with this approach. Despite its elegance, this approach does not yet form the basis for a convincing practical device because of the required large volume of volatile organic solvent and high quantities of specialty chemicals. We believe that a membrane based sensing approach with modern ion-selective electrode materials is required to achieve this goal.
We show here that a liquid membrane based coulometric ion detector can be achieved by utilizing membrane components typically used in polymeric ion-selective electrodes and with membranes that exhibit ion-exchanger properties. A common ion that is potential determining at both interfaces greatly simplifies the theoretical understanding of these systems relative to earlier cell designs, where the cation extraction at one interface was typically electrochemically coupled to an anion extraction step at the other side. (20) With thin membranes or membranes that have high ion mobilities, as desired in coulometry, this would be problematic because these two ions may eventually meet and result in significant water uptake with associated swelling and opacity increase of the membrane. (21) As an important other benefit, the approach introduced here also allows one to monitor the open circuit potential of the cell and to use this information to apply the correct potential for the coulometric readout step.

Experimental Section

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Reagents, Materials, and Equipment

Dodecyl 2-nitrophenyl ether (DDNPE), tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500), potassium tetrakis[3,4-bis(trifluoromethyl)phenyl]-borate (KTFPB), calcium ionophore IV (ETH 5234), high molecular weight poly(vinyl chloride) (PVC), tetrahydrofuran (THF), calcium chloride dihydrate, and potassium chloride were purchased in the highest quality available from Fluka. Aqueous solutions were prepared by dissolving the appropriate salts in Milli-Q-purified distilled water.
The polypropylene hollow fiber Accurel PP Q3/2 was supplied by Membrana GmbH (Wuppertal, Germany), and Sterling Silver Round wires of 250 and 500 μm i.d. were supplied by AEMETAL (Sydney, Australia).
Unless otherwise specificied, all measurements were performed at room temperature vs a double-junction Ag/AgCl/sat. KCl/1 M LiOAc reference electrode (Mettler-Toledo AG, Schwerzenbach, Switzerland) placed in the outer aqueous solution. The ion-selective hollow fiber cell served as the working electrode, and a high surface area Pt electrode (MT Electrodes, Perth, Australia) served as the counter electrode in coulometric measurements. The potentiometric calibration was performed using a 16-channel EMF monitor (Lawson Laboratories, Inc., Malvern, PA) connected to a personal computer. The coulometric measurements were performed with an Autolab PGSTAT128N (Metrohm Autolab, Utrecht, The Netherlands) attached to a personal computer. Calibrations were performed by feeding the cell with appropriate solutions using an ISMATEC peristaltic pump (Glattbrugg, Switzerland) with a flow rate of 25 μL·min−1.

Preparation of the Coulometric System

Silver wires of 15 cm in length and 250 (for the twisted configuation) or 500 μm diameter were cleaned with acetone and water before chlorination. A 9 cm section of the cleaned wire was dipped in a 1 M HCl solution. A potential of 0.5 V against double junction reference electrode was applied between the silver wire and the high surface area platinum counter electrode. The process was carried out for 2 min. The silver/silver chloride wire was rinsed thoroughly with distilled water after chlorination.
The polypropylene porous tube of 600 μm inner diameter, 200 μm wall thickness, and 7 cm length was washed inside and out with distilled water and THF. The chlorinated part of the wire was introduced into the polypropylene tube to its entire length. Two polypropylene pipet tips were used as fluidic connections for the flow-through system. The bare, nonchlorinated part of the silver wire was directed through the outlet tip to allow for the electrical connection. After assembly, the porous fiber was doped with 200 μL of the membrane cocktail composed of 266.7 mg of DDNPE, 30 mg (10 wt %) of ETH 500, 2.4 mg (10 mmol·kg−1) of Ca-ionophore IV, 0.9 mg of KTFPB (30 mol % relative to the ionophore), and 1.5 mL of THF.
The obtained ion-selective membrane was left to dry overnight, and any excess of the liquid membrane was wiped off with tissue paper. A PVC slurry was used to seal the inlet and outlet of the cell. The resulting inner active surface area of the membrane was about 113 mm2, as estimated from the nominal dimensions. A silicone tube was fixed to the inlet of the cell and connected to the peristaltic pump. The inner side of the cell was washed for a day by continuously flowing 1 mM CaCl2 solution at the flow rate mentioned above.

Procedures

A potentiometric calibration was performed using a silver/silver chloride wire immersed in the outer solution of a fixed composition (10−3 M CaCl2 + 10−2 M KCl) connected to the potentiometer as indicator electrode while the silver/silver chloride inside the hollow fiber membrane was connected to the reference port. Sample solutions of a fixed 10−5, 5 × 10−4, 10−4, 5 × 10−3, and 10−3 M CaCl2 concentration and with 10−2 M KCl as background electrolyte were continuously passed through the polypropylene tube, and the associated potential changes in the cell were recorded. The activities of calcium ion and the liquid junction potential were corrected with the Debye−Hückel approximation and the Henderson equation.
All other experiments were performed in a 3-electrode system with the silver/silver chloride wire inside the hollow fiber, which now acted as the working electrode. The same outer solution as above was used (10−3 M CaCl2 + 10−2 M KCl). The peristaltic pump was always off during the following measurements. For the current interruption test, four alternative +1 μA and −1 μA 3 s long pulses were applied with 30 s regeneration pulses at 0 A current following and preceding each pulse. Normal pulse voltammetry was performed within a range of 250 mV starting from the open circuit potential (OCP) and going toward more positive values. Potential pulses (1 s) in 10 mV potential increment were followed by 5 s OCP regeneration pulses (baseline potential). For the coulometric analysis procedure, three pulses were applied. An initial 20 s pulse at the OCP confirmed the stability of the system, followed by a 30 s OCP + n·25 mV calcium extracting pulse (n ranging from 1 to 10). A third 60 s pulse at OCP was used to regenerate the system before a new portion of sample was delivered to the active electrode area.

Results and Discussion

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In order to maximize the ion mobility of the membrane, porous polypropylene tubing was doped with a membrane containing plasticizer without the use of traditional poly(vinyl chloride) (PVC). Similar hollow fiber membrane materials were introduced by the group of Buffle as permeation membrane sampling systems. (22) Preliminary experiments on similarly formulated 20 μm thick Celgard membranes showed that membranes without any PVC did not exhibit a long operational lifetime with the traditional plasticizer bis(2-ethyl hexyl sebacate) (DOS). This might be due to nonoptimal casting conditions, using the solvent THF in the membrane cocktail slurry. Earlier work on doping 20 μm thin Celgard membranes (based on porous polypropylene as well) with DOS yielded functional membranes for a period of 1 to 2 days, (23) which is expected to improve with the much thicker tubular membrane used here (200 μm). To eliminate potential issues with limited lifetime, the plasticizer dodecyl 2-nitrophenyl ether, a more lipophilic analog of o-NPOE, was used. This solvent has been used in ion-selective electrode applications for over 30 years and exhibits an estimated octanol−water partition coefficient of log P = 7.4, 2 orders of magnitude larger than that of o-NPOE. (24) It was found earlier in optical bead based sensors to exhibit desirable lipophilicity characteristics as well, without apparent deteriorating influence on ion selectivity. (25) Note that polar (yet lipophilic) plasticizers are known to result in membranes with improved selectivity characteristics for divalent ions such as calcium (26) and, hence, was preferred here.
The membranes also contained the lipophilic electrolyte ETH 500 to keep the resistance of the membranes as low as possible, in analogy to earlier work. (15, 16, 20) The resistance was estimated with the current interrupt method (±1 μA) as 20.3 ± 0.5 kOhm. The use of the calcium ionophore ETH 5234 was explored in this initial study because of its high selectivity (27, 28) (higher also compared to the well-known ETH 1001) and large complex formation constant with calcium, (29) which affords a wide potential window for electrochemically mediated calcium extraction. The membrane was planned to exhibit cation-exchanger properties, which was achieved with the well known tetraphenylborate derivative KTFPB. On the basis of established ion-selective electrode theory, (10) the countercation of the ion-exchanger will exchange with calcium during a conditioning step, which renders the calcium activity in the membrane largely independent of the calcium activity in the contacting aqueous phase. Under these circumstances, the open circuit potential across the membrane follows the established Nernst equation, which is used here to monitor the concentration changes in the cell and to apply a correct excitation potential. A chloridized silver wire of 500 μm diameter was inserted into the polyprolyene tubing of nominally 600 μm inner diameter, leaving sufficient room for the fluidic delivery of the thin layer sample solution. As shown in Scheme 1, the cell was completed by inserting the tubing into an aqueous solution of 1 mM CaCl2 + 10 mM KCl, in which the counter and reference electrodes were placed.

Scheme 1

Scheme 1. Schematic of the Thin Layer Ion-Selective Coulometric System Presented Here, Consisting of a Hollow Fiber Based Calcium-Selective Working Electrode, a High Surface Area Pt Counter Electrode, and a Double Junction Ag/AgCl Reference Electrode Immersed in 1 mM CaCl2 + 10 mM KCla
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Scheme aThe working electrode is a 500 μm thick Ag/AgCl wire within the 600 μm i.d. polypropylene hollow fiber doped with 10 wt % ETH 500, 10 mmol·kg−1 Ca-ionophore IV, and 30 mol % (relative to the ionophore) of ion-exchanger KTFPB in DDNPE as a calcium-selective membrane. Sample solutions pass through the tubular electrode to form a thin sample layer (b) between the wire (a) and the membrane (c), while the wire is connected to the potentiostat at (d).

Note that asymmetric bathing conditions on either side of the liquid membrane may result in undesired ion countertransport processes, and a potentiometric monitoring of the transmembrane potential allows one to conveniently evaluate concentration changes in the thin layer sample with time. Figure 1 demonstrates the potentiometric response as a function of the thin layer sample composition, ranging from 10−5 to 10−2 M CaCl2 in a 10 mM KCl background electrolyte. Indeed, the near-Nernstian response slope suggests that the thin layer sample composition is sufficiently unperturbed by the outside bathing solution. The slight deviation from Nernstian behavior at high concentration can be quantitatively explained by the increasing chloride activity, which has an influence on the potential at the contacting silver/silver chloride electrode, as evidenced by the corrected data on the same plot. On the basis of the concentration excess of potassium ion on either side of the membrane, the Nernstian response also demonstrates a high selectivity to calcium ions, as expected for this ionophore (logKCa,Kpot = −9.3). (28) To our knowledge, this marks the first time that a hollow fiber membrane is reported as an ion-selective membrane in potentiometry.

Figure 1

Figure 1. Potentiometric calibration curve for the hollow fiber based calcium-selective electrode with an inner thin layer sample solution ranging from 10−5 to 10−2 M CaCl2 in a 10 mM KCl background electrolyte. The outer solution is constant at 1 mM CaCl2 + 10 mM KCl. The straight line is the least-squares fit between logarithmic concentrations of −5 and −3, with a slope of 29.6 mV per 10-fold concentration change.

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The ion-selective calcium membrane was subsequently explored for operation in a voltammetric detection mode. Earlier work with plasticized PVC membranes containing an ion-exchanger salt exhibited essentially featureless ohmic response characteristics at elevated sample concentrations, according to the Nernst equation and ohmic drop. (21) This result was one key reason why further work on voltammetric sensors avoided ion-exchanger based membranes. (20) However, it is expected that a featureless ohmic response can only be observed when concentration polarizations in the contacting aqueous phases are negligible. (21) With thin layer samples or with low sample concentrations, one will likely observe a mass transport limited current response. This is schematically shown in Figure 2, where concentration dependent featureless ohmic responses at high concentrations for a primary ion I+ and a background ion J+ give way to a current−potential curve that assumes a well-defined limiting current within the potential window given by the two mentioned ohmic response curves.

Figure 2

Figure 2. Schematic presentation of the expected current−potential behavior of ion-exchanger based ion-selective membrane electrodes. The straight lines for the primary ion I+ and the background ion J+ are expected for high sample concentrations where sample depletion is negligible. The separation between the two lines is given by the membrane selectivity and the activity of the two ions. When mass transport of the primary ion in the aqueous phase becomes rate limiting, as with low concentrations or volumes, a limiting current that is linearly dependent on concentration is expected between the two straight lines that define the potential window.

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This behavior was first explored with normal pulse voltammetry, with a 200 μm twisted wire in the inner tubing compartment. Here, the inner sample volume is expected to be substantially large, resulting in acceptably small sample perturbation between measurement pulses compared to a larger silver wire diameter. In normal pulse voltammetry, a correct baseline potential value needs to be applied between pulses that allows the imposed membrane concentration polarizations to essentially return back to its original, unperturbed state. (14) This baseline potential, of course, must here be the open circuit potential, (30) which is experimentally accessible. The normal pulse voltammetry protocol, therefore, consists of observing the open circuit potential, confirming the absence of potential drift, applying this potential for a fixed amount of time, confirming a near-zero current response, and applying 1 s potential excitation pulses at given increments relative to this baseline potential.
Figure 3 demonstrates the resulting current responses for the mass transport of calcium from the inner compartment of the tubing into the membrane and outside solution. Clearly, the currents are limited by calcium mass transport, as evidenced by the linear relationship between current plateau and calcium concentration. Note that, at potentials near the baseline potential, an ohmic response to calcium can be discerned, while at large potential increments beyond the current plateau, the ohmic behavior toward the background ion potassium is observed. The potential window for the plateau is a function of the ion selectivity of the membrane and the composition of the sample solution. This behavior compares well to that schematically shown in Figure 2.

Figure 3

Figure 3. Normal pulse voltammograms obtained for a hollow fiber based system with an increased volume of inner sample solution (smaller diameter silver wire) containing varying concentrations of CaCl2 in a constant background of 10 mM KCl, while the outer solution consists of a constant 1 mM CaCl2 + 10 mM KCl. Note the concentration dependent limiting currents for this ion-exchanger based membrane system that compare to Figure 2.

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To explore a thin layer coulometric operation of the tubular membrane, a thicker chloridized silver wire was inserted, as for the potentiometric data presented in Figure 1. The protocol for the coulometric detection was similar as for normal pulse voltammetry. The open circuit potential was monitored to confirm the absence of potential drifts, and subsequently, this potential was applied, confirming very low current readings. A potential increment was then applied relative to the open circuit potential, now for a longer period to allow for the exhaustive depletion of the thin layer sample. Subsequently, the open circuit potential was again applied to return the membrane to its unperturbed state and to regenerate the silver chloride wire. (14, 31, 32) The thin layer sample solution was replaced with a fresh sample before applying the next measurement.
Figure 4 shows the observed current decays for the indicated potential increments (shown as ΔE, the applied potential minus the open circuit potential) for three different sample concentrations: (A) 1.0 × 10−5 M, (B) 2.5 × 10−5 M, and (C) 5.0 × 10−5 M. Note that the initial current responses follow Ohm’s law, similar to that shown in Figure 2, since thin layer sample depletion is negligible at short measurement times. Subsequently, the currents decay within the 30 s time period. For the 25 μM calcium sample at a ΔE of 150 mV, for example, the initial current of 27.4 μA reduces to 1.2 μA. The data also show that, with increasing potential, the current decay curves start to essentially overlap, which is consistent with an exhaustive mass transport limited process. Note, however, the increasing current amplitudes for 10 μM calcium with larger applied potentials (above 175 mV relative to the open circuit potential) in Figure 4, which do not decay to zero at long times. This is clearly due to concurrent extraction of potassium at the higher applied potential, resulting in interference. It is anticipated that extended measurement protocols that incorporate an in situ background subtraction step may distinguish to some extent between electrolyte that exhaustively depletes and more concentrated background electrolyte that does not. Such studies will be forthcoming in future work.

Figure 4

Figure 4. Chronoamperograms obtained for a thin layer (500 μm thick Ag/AgCl wire) coulometric system for samples of (A) 1 × 10−5 M, (B) 2.5 × 10−5 M, and (C) 5 × 10−5 M CaCl2 all in a 10 mM KCl background during various 30 s potential pulses vs open circuit potential, as indicated on the graph. Other conditions as in Figure 3.

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Figure 5A illustrates the calculated charge for the individual current responses as a function of applied potential (vs open circuit potential) for different calcium concentrations. Clearly, a potential window exists where the charge is strongly concentration dependent, which confirms that thin layer coulometric readout is indeed dependent on the calcium level in the thin layer sample. The width of this potential window is dependent on the selectivity of the membrane, with higher levels of interference diminishing the potential window. In a practical protocol, the measured open circuit potential and the available potential window may likely allow one to apply appropriate potentials that can be applied to samples of variable composition. Note that there is some increase of the observed charge with applied potential within the aforementioned potential window, which is mainly explained by non-Faradaic charging currents, which have here not yet been corrected for. For comparison, the data are replotted in Figure 5B as applied potential vs Ag/AgCl, in which case the response toward the KCl background electrolyte can be better visualized. Further work will explore in situ background correction protocols to minimize this contribution.

Figure 5

Figure 5. Calculated charge as a function of applied potential (A) vs open circuit potential and (B) vs Ag/AgCl wire for the calcium concentration indicated on the graphs. Other conditions as in Figure 4.

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Repeated injections of three identical calcium samples and of samples with varying calcium concentration in a background of 10 mM KCl were performed and measured at an applied potential of 150 mV more positive than the open circuit potential. The observed current decays for the different concentrations are shown in Figure 6, while the calculated charge as a function of concentration is illustrated in the inset. No background correction was performed to best illustrate the raw performance of the system. The expected linear relationship between charge and calcium concentration is indeed observed. The nonspecific processes discussed above give a contribution of 25 μC to the background. The repeatability is very good for the initial system presented here, with relative standard deviations ranging from 0.11% for 10 μM calcium to 0.90% for 100 μM calcium (N = 3). While the focus of this study was to introduce the underlying response principles, it is noted that higher calcium concentrations started to deviate from the calibration curve in Figure 6. For these concentrations, the electrolysis time of 30 s was not sufficiently long, as evidenced by current decays that were not exhaustive. Longer detection times, thinner membrane tubing, larger pore size of the membrane support, increased mobility within the membrane, and a thinner sample layer are all expected to increase the upper limit of detection. Higher detection limits were observed with the thin layer coulometry work of Kihara, for example, who used bulk organic solvents as the sensing phase. (19) The slope of the least-squares fit of the calibration curve (0.882 μC/M) was found 10 days later as 0.868 μC/M. As a typical example, the relative deviations in this time period of the determined charge were on the order of 2% for 50 and 75 μM concentrations of calcium.

Figure 6

Figure 6. Chronoamperograms of the thin layer system for the sample concentrations indicated on the graph (other conditions as in Figure 4). Here, the potential applied for individual concentrations was always 150 mV vs open circuit potential. The inset presents the calculated charge as a function of sample concentration from the chronoamperograms shown, confirming linear behavior.

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Conclusions

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The study presented in this article demonstrates potential controlled thin layer coulometry with ionophore based ion-selective membranes as a new technique for aqueous sample analysis. It was shown that the newly designed flow-through system consisting of a hollow fiber based ion-selective membrane and a silver/silver chloride inner electrode exhibits a potentiometric response behavior typical of a potentiometric ion-selective electrode. More importantly, it was found that an applied potential pulse forced the selective transport of the primary ion from the thin layer sample solution through the membrane and into the outer solution. The process occurs until the sample is exhausted which results in a monitored current decay. The charge calculated from the generated signal is indeed linearly related to the sample concentration. The relative standard deviation observed for several repeated sample measurements was found to be below 1% and within a time period of 10 days on the order of 2%, making this work a promising initial step toward calibration-free analysis. An effective, in situ evaluation and correction of non-Faradaic charging currents and a more thorough theoretical study are underway to further develop this promising methodology.

Author Information

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  • Corresponding Author
    • Eric Bakker - Department of Chemistry, Nanochemistry Research Institute, Curtin University of Technology, Perth, WA 6845, Australia
  • Author
    • Ewa Grygolowicz-Pawlak - Department of Chemistry, Nanochemistry Research Institute, Curtin University of Technology, Perth, WA 6845, Australia

Acknowledgment

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The authors are grateful to the Australian Research Council (DP0987851), the CSIRO through the Flagship Cluster “Sensors Systems for Analysis of Aquatic Environments”, and the National Institutes of Health (R01-EB002189) for financial support of this research.

References

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This article references 32 other publications.

  1. 1
    Miller, R. L., Del Castillo, C. E., and McKee, B. A., Eds. Remote Sensing of Coastal Aquatic Environments. Technologies, Techniques and Applications; Springer: Secaucus, NJ, 2005.
    Google Scholar
    There is no corresponding record for this reference.
  2. 2
    Lee, H. J., Yoon, I. J., Yoo, C. L., Pyun, H.-J., Cha, G. S., and Nam, H. Anal. Chem. 2000, 72, 4694– 4699
    Google Scholar
    There is no corresponding record for this reference.
  3. 3
    Wang, J. and Tian, B. Anal. Chem. 1992, 64, 1706– 1709
    Google Scholar
    There is no corresponding record for this reference.
  4. 4
    Jacobs, E., Ancy, J. J., and Smith, M. Point Care: J. Near-Patient Test. Technol. 2002, 1, 135– 144
    Google Scholar
    There is no corresponding record for this reference.
  5. 5
    Bakker, E., Bhakthavatsalam, V., and Gemene, K. L. Talanta 2008, 75, 629– 635
    Google Scholar
    There is no corresponding record for this reference.
  6. 6
    Bard, A. J. Anal. Chem. 1966, 38, 88R– 98R
    Google Scholar
    There is no corresponding record for this reference.
  7. 7
    Oglesby, D. M., Anderson, L. B., McDuffie, B., and Reilley, C. N. Anal. Chem. 1965, 37, 1317– 1321
    Google Scholar
    There is no corresponding record for this reference.
  8. 8
    Tsujimura, S., Kojima, S., Ikeda, T., and Kano, K. Anal. Bioanal. Chem. 2006, 386, 645– 651
    Google Scholar
    8
    Potential-step coulometry of D-glucose using a novel FAD-dependent glucose dehydrogenase
    Tsujimura, Seiya; Kojima, Shinki; Ikeda, Tokuji; Kano, Kenji
    Analytical and Bioanalytical Chemistry (2006), 386 (3), 645-651CODEN: ABCNBP; ISSN:1618-2642. (Springer)
    This paper describes the construction and characterization of a batch-type coulometric system for the detection of D-glucose using a novel FAD-dependent glucose dehydrogenase. To overcome the problem of interferents, such as ascorbate and urate, a potential-step method was proposed to sep. the electrolysis reactions of interferents and D-glucose by selecting a mediator possessing an appropriate formal potential. The rapid oxidative consumption of the interferents proceeded in the first step, whereas the mediator and glucose remained reduced. In the second step, the mediator was immediately oxidized, and subsequent bioelectrocatalytic oxidn. of D-glucose occurred with the aid of aldose 1-epimerase. In this study, potassium octacyanomolybdate (IV) with a formal potential of 0.6 V vs. Ag|AgCl was chosen as a mediator, and the first and second electrolysis potentials were set at 0.4 V and 0.8 V, resp., by considering the heterogeneous electron-transfer kinetics and the potential window. The background-cor. response in charge corresponded to 99±2 % efficiency in terms of the amt. of D-glucose.
  9. 9
    Buhlmann, P., Pretsch, E., and Bakker, E. Chem. Rev. 1998, 98, 1593– 1687
    Google Scholar
    There is no corresponding record for this reference.
  10. 10
    Bakker, E., Buhlmann, P., and Pretsch, E. Chem. Rev. 1997, 97, 3083– 3132
    Google Scholar
    10
    Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 1. General Characteristics
    Bakker, Eric; Buehlmann, Philippe; Pretsch, Ernoe
    Chemical Reviews (Washington, D. C.) (1997), 97 (8), 3083-3132CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review, with 322 refs., is given on the relation of the response of carrier-based ion-selective electrodes and bulk optodes.
  11. 11
    Bakker, E. and Pretsch, E. Angew. Chem., Int. Ed. 2007, 46, 2– 11
    Google Scholar
    There is no corresponding record for this reference.
  12. 12
    Samec, Z., Samcova, E., and Girault, H. H. Talanta 2004, 63, 21– 32
    Google Scholar
    There is no corresponding record for this reference.
  13. 13
    Kim, Y. and Amemiya, S. Anal. Chem. 2008, 80, 6056– 6065
    Google Scholar
    13
    Stripping Analysis of Nanomolar Perchlorate in Drinking Water with a Voltammetric Ion-Selective Electrode Based on Thin-Layer Liquid Membrane
    Kim, Yushin; Amemiya, Shigeru
    Analytical Chemistry (Washington, DC, United States) (2008), 80 (15), 6056-6065CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    A highly sensitive anal. method is required to assess nano-molar perchlorate pollution in drinking water as an emerging environmental problem. A novel approach, based on a voltammetric ion-selective electrode for the electrochem. detection of redox-inactive perchlorate at a nano-molar concn. without its electrolysis was developed. The perchlorate-selective electrode is based on a sub-micrometer-thick, plasticized poly(vinyl chloride) membrane spin-coated on a poly(3-octylthiophene)-modified Au electrode. The liq. membrane serves as the first thin-layer cell for ion-transfer stripping voltammetry to give low detection limits of 0.2-0.5 nM perchlorate in deionized water, com. bottled water, and tap water under a rotating electrode configuration. Detection limits were much lower than the USEPA action limit (∼246 nM) and were comparable to detection limits of the most sensitive anal. methods for detecting perchlorate, i.e., ion chromatog. in conjunction with suppressed cond. detection (0.55 nM) or electro-spray ionization mass spectrometry (0.20-0.25 nM). Perchlorate mass transfer in the thin-layer liq. membrane and aq. sample and its transfer at the interface between the 2 phases were exptl. and theor. examd. to achieve the low detection limits. Advantages of ion-transfer stripping voltammetry with a thin-layer liq. membrane vs. traditional ion-selective potentiometry were demonstrated in terms of detection limit, response time, and selectivity.
  14. 14
    Jadhav, S., Meir, A. J., and Bakker, E. Electroanalysis 2000, 12, 1251– 1257
    Google Scholar
    There is no corresponding record for this reference.
  15. 15
    Shvarev, A. and Bakker, E. Anal. Chem. 2003, 75, 4541– 4550
    Google Scholar
    There is no corresponding record for this reference.
  16. 16
    Gemene, K. and Bakker, E. Anal. Chem. 2008, 80, 3743– 3750
    Google Scholar
    There is no corresponding record for this reference.
  17. 17
    Sanchez-Pedreno, C., Ortuno, J. A., and Hernandez, J. Anal. Chim. Acta 2002, 459, 11– 17
    Google Scholar
    There is no corresponding record for this reference.
  18. 18
    Sawada, S., Taguma, M., Kimoto, T., Hotta, H., and Osakai, T. Anal. Chem. 2002, 74, 1177– 1181
    Google Scholar
    There is no corresponding record for this reference.
  19. 19
    Yoshizumi, A., Uehara, A., Kasuno, M., Kitatsuhi, Y., Yoshida, Z., and Kihara, S. J. Electroanal. Chem. 2005, 581, 275– 283
    Google Scholar
    There is no corresponding record for this reference.
  20. 20
    Jadhav, S. and Bakker, E. Anal. Chem. 2001, 73, 80– 90
    Google Scholar
    There is no corresponding record for this reference.
  21. 21
    Jadhav, S. and Bakker, E. Anal. Chem. 1999, 71, 3657– 3664
    Google Scholar
    There is no corresponding record for this reference.
  22. 22
    Ueberfeld, J., Parthasarathy, N., Zbinden, H., Gisin, N., and Buffle, J. Anal. Chem. 2002, 74, 664– 670
    Google Scholar
    There is no corresponding record for this reference.
  23. 23
    Malon, A., Bakker, E., and Pretsch, E. Anal. Chem. 2007, 79, 632– 638
    Google Scholar
    There is no corresponding record for this reference.
  24. 24
    Oesch, U. and Simon, W. Anal. Chem. 1980, 52, 692– 700
    Google Scholar
    24
    Lifetime of neutral carrier based ion-selective liquid-membrane electrodes
    Oesch, Urs; Simon, Wilhelm
    Analytical Chemistry (1980), 52 (4), 692-700CODEN: ANCHAM; ISSN:0003-2700.
    Models for the estn. of the lifetime of neutral-carrier-based ion-selective liq.-membrane electrodes are presented. They are based on the kinetics of loss of plasticizer and/or ionophore from the solvent polymeric membrane phase into the sample soln. The exptl. obsd. lifetime is in good agreement with the theor. estd. value. For anal. relevant membrane systems, both the ion carrier and the plasticizer used should have partition coeffs. between sample and membrane larger than ∼106 to ensure a continuous-use lifetime of at least 1 yr.
  25. 25
    Telting-Diaz, M. and Bakker, E. Anal. Chem. 2002, 74, 5251– 5256
    Google Scholar
    There is no corresponding record for this reference.
  26. 26
    Anker, P., Ammann, D., Asper, R., Dohner, R. E., Simon, W., and Wieland, E. Anal. Chem. 1981, 53, 1970– 1974
    Google Scholar
    There is no corresponding record for this reference.
  27. 27
    Gehrig, P., Rusterholz, B., and Simon, W. Chimia 1989, 43, 377– 379
    Google Scholar
    There is no corresponding record for this reference.
  28. 28
    Bhakthavatsalam, V., Shvarev, A., and Bakker, E. Analyst 2006, 131, 895– 900
    Google Scholar
    There is no corresponding record for this reference.
  29. 29
    Qin, Y., Mi, Y., and Bakker, E. Anal. Chim. Acta 2000, 421, 207– 220
    Google Scholar
    29
    Determination of complex formation constants of 18 neutral alkali and alkaline earth metal ionophores in poly(vinyl chloride) sensing membranes plasticized with bis(2-ethylhexyl)sebacate and o-nitrophenyloctylether
    Qin, Y.; Mi, Y.; Bakker, E.
    Analytica Chimica Acta (2000), 421 (2), 207-220CODEN: ACACAM; ISSN:0003-2670. (Elsevier Science B.V.)
    A segmented sandwich membrane method is used to det. complex formation consts. of 18 elec. neutral ionophores in situ in solvent polymeric sensing membranes. These ionophores are commonly used in potentiometric and optical sensors, and knowledge of such binding information is important for ionophore and sensor design. In this method, two membrane segments are fused together, with only one contg. the ionophore, to give a concn.-polarized sandwich membrane. Unlike other approaches, this method does not require the use of a ref. ion in the sample and/or a 2nd ionophore in the membrane, and is typically pH insensitive. The following ionophores responsive for the common cations lithium, sodium, potassium, magnesium and calcium are characterized and discussed: valinomycin, BME-44, bis[(benzo-15-crown-5)-4'-ylmethyl]pimelate, ETH 157, ETH 2120, bis[(12-crown-4)methyl]dodecylmethylmalonate, 4-tert-butylcalix [4] arene tetraacetic acid tetra-Et ester, ETH 149, ETH 1644, ETH 1810, 6,6-dibenzyl-14-crown-4, N,N,N',N',N'',N''-hexacyclohexyl-4,4',4''-propylidyne tris(3-oxabutyramide), ETH 1117, ETH 4030, ETH 1001, ETH 129, ETH 5234, and A23187. The logarithmic complex formation consts. range from 4.4 to 29 and compare well to published data for ionophores that were characterized earlier. From the obsd. complex formation consts., max. possible selectivities are calcd. that would be expected if interfering ions show no binding affinity to the ionophore, and the values are compared with exptl. findings. Each ionophore is characterized in poly(vinyl chloride) membranes plasticized either with a polar (NPOE) or a nonpolar plasticizer (DOS). Membranes based on NPOE always show larger complex formation consts. of the embedded ionophore.
  30. 30
    Shvarev, A. and Bakker, E. Anal. Chem. 2005, 77, 5221– 5228
    Google Scholar
    30
    Response Characteristics of a Reversible Electrochemical Sensor for the Polyion Protamine
    Shvarev, Alexey; Bakker, Eric
    Analytical Chemistry (2005), 77 (16), 5221-5228CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    The authors describe here in detail the first reversible electrochem. sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the detn. of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequil. extn. of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extn. and ion stripping are now fully controlled electrochem. Spontaneous polyion extn. is avoided by using membranes contg. highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extn. of polyions is induced if a const. current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theor. response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochem. sensing system is characterized in terms of optimal working conditions, membrane compn., selectivity, and influence of sample stirring and org.-phase diffusion coeff. on the response characteristics. Excellent potential stability and reversibility of the sensors are obsd., and measurements of heparin concn. in whole blood samples via protamine titrn. are demonstrated.
  31. 31
    Bakker, E. and Meir, A. J. SIAM Rev. 2003, 45, 327– 344
    Google Scholar
    There is no corresponding record for this reference.
  32. 32
    Zook, J. M. and Lindner, E. Anal. Chem. 2009, 81, 5155– 5164
    Google Scholar
    There is no corresponding record for this reference.

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  2. Yujie Liu, Gastón A. Crespo, María Cuartero. Voltammetric Ion-Selective Electrodes in Thin-Layer Samples: Absolute Detection of Ions Using Ultrathin Membranes. Analytical Chemistry 2024, 96 (3) , 1147-1155. https://doi.org/10.1021/acs.analchem.3c04224
  3. Xing Xuan, Clara Pérez-Ràfols, Chen Chen, Maria Cuartero, Gaston A. Crespo. Lactate Biosensing for Reliable On-Body Sweat Analysis. ACS Sensors 2021, 6 (7) , 2763-2771. https://doi.org/10.1021/acssensors.1c01009
  4. Sutida Jansod, Eric Bakker. Tunable Optical Sensing with PVC-Membrane-Based Ion-Selective Bipolar Electrodes. ACS Sensors 2019, 4 (4) , 1008-1016. https://doi.org/10.1021/acssensors.9b00179
  5. Jiawang Ding, Nana Yu, Xuedong Wang, and Wei Qin . Sequential and Selective Detection of Two Molecules with a Single Solid-Contact Chronopotentiometric Ion-Selective Electrode. Analytical Chemistry 2018, 90 (3) , 1734-1739. https://doi.org/10.1021/acs.analchem.7b03522
  6. Xénia Nagy and Lajos Höfler . Lowering Detection Limits Toward Target Ions Using Quasi-Symmetric Polymeric Ion-Selective Membranes Combined with Amperometric Measurements. Analytical Chemistry 2016, 88 (19) , 9850-9855. https://doi.org/10.1021/acs.analchem.6b03043
  7. Majid Ghahraman Afshar, Gastón A. Crespo, and Eric Bakker . Flow Chronopotentiometry with Ion-Selective Membranes for Cation, Anion, and Polyion Detection. Analytical Chemistry 2016, 88 (7) , 3945-3952. https://doi.org/10.1021/acs.analchem.6b00141
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  9. Majid Ghahraman Afshar, Gastón A. Crespo, and Eric Bakker . Coulometric Calcium Pump for Thin Layer Sample Titrations. Analytical Chemistry 2015, 87 (19) , 10125-10130. https://doi.org/10.1021/acs.analchem.5b02856
  10. Jiawang Ding, Yue Gu, Fei Li, Hongxia Zhang, and Wei Qin . DNA Nanostructure-Based Magnetic Beads for Potentiometric Aptasensing. Analytical Chemistry 2015, 87 (13) , 6465-6469. https://doi.org/10.1021/acs.analchem.5b01576
  11. Maria Cuartero, Gastón A. Crespo, and Eric Bakker . Paper-Based Thin-Layer Coulometric Sensor for Halide Determination. Analytical Chemistry 2015, 87 (3) , 1981-1990. https://doi.org/10.1021/ac504400w
  12. Ulriika Vanamo and Johan Bobacka . Instrument-Free Control of the Standard Potential of Potentiometric Solid-Contact Ion-Selective Electrodes by Short-Circuiting with a Conventional Reference Electrode. Analytical Chemistry 2014, 86 (21) , 10540-10545. https://doi.org/10.1021/ac501464s
  13. Zdeňka Jarolímová, Gastón A. Crespo, Xiaojiang Xie, Majid Ghahraman Afshar, Marcin Pawlak, and Eric Bakker . Chronopotentiometric Carbonate Detection with All-Solid-State Ionophore-Based Electrodes. Analytical Chemistry 2014, 86 (13) , 6307-6314. https://doi.org/10.1021/ac5004163
  14. Gastón A. Crespo, Majid Ghahraman Afshar, Denis Dorokhin, and Eric Bakker . Thin Layer Coulometry Based on Ion-Exchanger Membranes for Heparin Detection in Undiluted Human Blood. Analytical Chemistry 2014, 86 (3) , 1357-1360. https://doi.org/10.1021/ac403902f
  15. Majid Ghahraman Afshar, Gastón A. Crespo, and Eric Bakker . Direct Ion Speciation Analysis with Ion-Selective Membranes Operated in a Sequential Potentiometric/Time Resolved Chronopotentiometric Sensing Mode. Analytical Chemistry 2012, 84 (20) , 8813-8821. https://doi.org/10.1021/ac302092m
  16. Alexey Shvarev, Bastien Neel, and Eric Bakker . Detection Limits of Thin Layer Coulometry with Ionophore Based Ion-Selective Membranes. Analytical Chemistry 2012, 84 (18) , 8038-8044. https://doi.org/10.1021/ac301940n
  17. Ewa Grygolowicz-Pawlak, Manzar Sohail, Marcin Pawlak, Bastien Neel, Alexey Shvarev, Roland de Marco, and Eric Bakker . Coulometric Sodium Chloride Removal System with Nafion Membrane for Seawater Sample Treatment. Analytical Chemistry 2012, 84 (14) , 6158-6165. https://doi.org/10.1021/ac301096r
  18. Ewa Grygolowicz-Pawlak, Apon Numnuam, Panote Thavarungkul, Proespichaya Kanatharana, and Eric Bakker . Interference Compensation for Thin Layer Coulometric Ion-Selective Membrane Electrodes by the Double Pulse Technique. Analytical Chemistry 2012, 84 (3) , 1327-1335. https://doi.org/10.1021/ac202273k
  19. Eric Bakker. Membrane Response Model for Ion-Selective Electrodes Operated by Controlled-Potential Thin-Layer Coulometry. Analytical Chemistry 2011, 83 (2) , 486-493. https://doi.org/10.1021/ac102016y
  20. D. Yureka Imali, E. Chavin J. Perera, M. N. Kaumal, Dhammike P. Dissanayake. Conducting polymer functionalization in search of advanced materials in ionometry: ion-selective electrodes and optodes. RSC Advances 2024, 14 (35) , 25516-25548. https://doi.org/10.1039/D4RA02615B
  21. R.A. Fernández, F.M. Zanotto, S.A. Dassie. Theoretical insights into homogeneous catalysis impact on ion transfer-electron transfer coupled processes at thick-film modified electrodes. Journal of Electroanalytical Chemistry 2024, 967 , 118456. https://doi.org/10.1016/j.jelechem.2024.118456
  22. Johan Bobacka. Perspective on the coulometric transduction principle for ion-selective electrodes. Sensors and Actuators B: Chemical 2024, 410 , 135674. https://doi.org/10.1016/j.snb.2024.135674
  23. Jiarong Zhao, Jiawang Ding, Feng Luan, Wei Qin. Chronopotentiometric sensors for antimicrobial peptide-based biosensing of Staphylococcus aureus. Microchimica Acta 2024, 191 (6) https://doi.org/10.1007/s00604-024-06410-4
  24. V. Shavokshina, A. Okoneshnikov, V. Nikitina, A. Karyakin. Amperometric Signal Generation by Self-Doped Polyanilines for Ion-Selective Electrodes. Journal of Analytical Chemistry 2024, 79 (6) , 740-748. https://doi.org/10.1134/S1061934824700126
  25. Junsong Mou, Jiawang Ding, Wei Qin. Modern Potentiometric Biosensing Based on Non‐Equilibrium Measurement Techniques. Chemistry – A European Journal 2023, 29 (72) https://doi.org/10.1002/chem.202302647
  26. Md Asaduzzaman, Md Abu Zahed, Md Sharifuzzaman, Md Selim Reza, Xue Hui, Sudeep Sharma, Young Do Shin, Jae Yeong Park. A hybridized nano-porous carbon reinforced 3D graphene-based epidermal patch for precise sweat glucose and lactate analysis. Biosensors and Bioelectronics 2023, 219 , 114846. https://doi.org/10.1016/j.bios.2022.114846
  27. Matthew T. Flavin, Charles A. Lissandrello, Jongyoon Han. Real-time, dynamic monitoring of selectively driven ion-concentration polarization. Electrochimica Acta 2022, 426 , 140770. https://doi.org/10.1016/j.electacta.2022.140770
  28. Miklós Márton Kovács, Martin Kis, Lajos Höfler. Detection of Marginally Discriminated Ions with Differential Solid Contact Ion-Selective Electrodes. Journal of The Electrochemical Society 2022, 169 (8) , 087515. https://doi.org/10.1149/1945-7111/ac876e
  29. Anna Kisiel, Agata Michalska, Krzysztof Maksymiuk. Bypassed ion-selective electrodes – self-powered polarization for tailoring of sensor performance. The Analyst 2022, 147 (12) , 2764-2772. https://doi.org/10.1039/D2AN00458E
  30. Matthew T. Flavin, Marek A. Paul, Alexander S. Lim, Charles A. Lissandrello, Robert Ajemian, Samuel J. Lin, Jongyoon Han. Electrochemical modulation enhances the selectivity of peripheral neurostimulation in vivo. Proceedings of the National Academy of Sciences 2022, 119 (23) https://doi.org/10.1073/pnas.2117764119
  31. Nurgul K. Bakirhan, Burcu D. Topal, Goksu Ozcelikay, Leyla Karadurmus, Sibel A. Ozkan. Current Advances in Electrochemical Biosensors and Nanobiosensors. Critical Reviews in Analytical Chemistry 2022, 52 (3) , 519-534. https://doi.org/10.1080/10408347.2020.1809339
  32. Shiho Tatsumi, Terumasa Omatsu, Kohji Maeda, Maral P.S. Mousavi, George M. Whitesides, Yumi Yoshida. An all-solid-state thin-layer laminated cell for calibration-free coulometric determination of K+. Electrochimica Acta 2022, 408 , 139946. https://doi.org/10.1016/j.electacta.2022.139946
  33. Huixin Liu, Zhen Gu, Qing Zhao, Shuai Li, Xi Ding, Xinxin Xiao, Guangli Xiu. Printed circuit board integrated wearable ion-selective electrode with potential treatment for highly repeatable sweat monitoring. Sensors and Actuators B: Chemical 2022, 355 , 131102. https://doi.org/10.1016/j.snb.2021.131102
  34. Dawid Kałuża, Agata Michalska, Krzysztof Maksymiuk. Solid‐Contact Ion‐Selective Electrodes Paving the Way for Improved Non‐Zero Current Sensors: A Minireview. ChemElectroChem 2022, 9 (1) https://doi.org/10.1002/celc.202100892
  35. Vita N. Nikitina, Ekaterina D. Maksimova, Marina D. Zavolskova, Arkady A. Karyakin. Flow injection amperometry as an alternative to potentiometry for solid contact ion-selective membrane-based electrodes.. Electrochimica Acta 2021, 377 , 138074. https://doi.org/10.1016/j.electacta.2021.138074
  36. Shuwen Liu, Jiawang Ding, Wei Qin. Chronopotentiometric aptasensing with signal amplification based on enzyme-catalyzed surface polymerization. Chemical Communications 2020, 56 (87) , 13355-13358. https://doi.org/10.1039/D0CC05745B
  37. Jiawang Ding, Wei Qin. Recent advances in potentiometric biosensors. TrAC Trends in Analytical Chemistry 2020, 124 , 115803. https://doi.org/10.1016/j.trac.2019.115803
  38. Ewa Jaworska, Paweł Pawłowski, Agata Michalska, Krzysztof Maksymiuk. Advantages of Amperometric Readout Mode of Ion‐selective Electrodes under Potentiostatic Conditions. Electroanalysis 2019, 31 (2) , 343-349. https://doi.org/10.1002/elan.201800649
  39. Matthew T. Flavin, Daniel K. Freeman, Jongyoon Han. Interfacial ion transfer and current limiting in neutral-carrier ion-selective membranes: A detailed numerical model. Journal of Membrane Science 2019, 572 , 374-381. https://doi.org/10.1016/j.memsci.2018.10.065
  40. Jiawang Ding, Thomas Cherubini, Dajing Yuan, Eric Bakker. Paper-supported thin-layer ion transfer voltammetry for ion detection. Sensors and Actuators B: Chemical 2019, 280 , 69-76. https://doi.org/10.1016/j.snb.2018.10.046
  41. Marc Parrilla, Maria Cuartero, Gaston A. Crespo. Wearable potentiometric ion sensors. TrAC Trends in Analytical Chemistry 2019, 110 , 303-320. https://doi.org/10.1016/j.trac.2018.11.024
  42. Emi Kusakabe, Yui Nakamura, Kohji Maeda, Mao Fukuyama, Yumi Yoshida. Effect of oxidation ratio of conducting polymer on potential stability of the conducting polymer-coated electrode in voltammetric cell for the ion transfer. Journal of Electroanalytical Chemistry 2018, 825 , 8-15. https://doi.org/10.1016/j.jelechem.2018.07.057
  43. 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
  44. M. Fighera, P. D. van der Wal, H. Shea. Microfluidic Platform for Seawater Desalination by Coulometric Removal of Chloride Ions through Printed Ag Electrodes. Journal of The Electrochemical Society 2017, 164 (12) , H836-H845. https://doi.org/10.1149/2.1761712jes
  45. Tingting Han, Ulriika Vanamo, Johan Bobacka. Influence of Electrode Geometry on the Response of Solid‐Contact Ion‐Selective Electrodes when Utilizing a New Coulometric Signal Readout Method. ChemElectroChem 2016, 3 (12) , 2071-2077. https://doi.org/10.1002/celc.201600575
  46. J. Justin Gooding, Katharina Gaus. Einzelmolekül‐Sensoren: Herausforderungen und Möglichkeiten für die quantitative Analyse. Angewandte Chemie 2016, 128 (38) , 11526-11539. https://doi.org/10.1002/ange.201600495
  47. J. Justin Gooding, Katharina Gaus. Single‐Molecule Sensors: Challenges and Opportunities for Quantitative Analysis. Angewandte Chemie International Edition 2016, 55 (38) , 11354-11366. https://doi.org/10.1002/anie.201600495
  48. J.A. Ortuño, J.M. Olmos, E. Torralba, A. Molina. Sensing and characterization of neurotransmitter 2-phenylethylamine based on facilitated ion transfer at solvent polymeric membranes using different electrochemical techniques. Sensors and Actuators B: Chemical 2016, 222 , 930-936. https://doi.org/10.1016/j.snb.2015.09.011
  49. Majid Ghahraman Afshar, Gastón A. Crespo, Denis Dorokhin, Bastien Néel, Eric Bakker. Thin Layer Coulometry of Nitrite with Ion‐Selective Membranes. Electroanalysis 2015, 27 (3) , 609-615. https://doi.org/10.1002/elan.201400522
  50. Stéphane Jeanneret, Gastón A. Crespo, Majid Ghahraman Afshar, Eric Bakker. GalvaPot, a custom-made combination galvanostat/potentiostat and high impedance potentiometer for decentralized measurements of ionophore-based electrodes. Sensors and Actuators B: Chemical 2015, 207 , 631-639. https://doi.org/10.1016/j.snb.2014.10.084
  51. Grégoire Herzog. Recent developments in electrochemistry at the interface between two immiscible electrolyte solutions for ion sensing. The Analyst 2015, 140 (12) , 3888-3896. https://doi.org/10.1039/C5AN00601E
  52. Yumi Yoshida, Junya Uchida, Shotaro Nakamura, Satoshi Yamaguchi, Kohji Maeda. Improved Thin-layer Electrolysis Cell for Ion Transfer at the Liquid|Liquid Interface Using a Conducting Polymer-coated Electrode. Analytical Sciences 2014, 30 (3) , 351-357. https://doi.org/10.2116/analsci.30.351
  53. Eric Bakker. Potentiometric Sensors. 2014, 193-238. https://doi.org/10.1007/978-1-4939-0676-5_9
  54. Eric Bakker. Enhancing ion-selective polymeric membrane electrodes by instrumental control. TrAC Trends in Analytical Chemistry 2014, 53 , 98-105. https://doi.org/10.1016/j.trac.2013.09.014
  55. Denis Dorokhin, Gastón A. Crespo, Majid Ghahraman Afshar, Eric Bakker. A low-cost thin layer coulometric microfluidic device based on an ion-selective membrane for calcium determination. The Analyst 2014, 139 (1) , 48-51. https://doi.org/10.1039/C3AN01715J
  56. Mohamed M. Marei, Thomas J. Roussel, Robert S. Keynton, Richard P. Baldwin. Electrochemical and microfabrication strategies for remotely operated smart chemical sensors: Application of anodic stripping coulometry to calibration-free measurements of copper and mercury. Analytica Chimica Acta 2013, 803 , 47-55. https://doi.org/10.1016/j.aca.2013.06.047
  57. Zdeňka Jarolímová, Gastón A. Crespo, Majid Ghahraman Afshar, Marcin Pawlak, Eric Bakker. All solid state chronopotentiometric ion-selective electrodes based on ferrocene functionalized PVC. Journal of Electroanalytical Chemistry 2013, 709 , 118-125. https://doi.org/10.1016/j.jelechem.2013.10.011
  58. M. Sohail, R. De Marco. ELECTRODES | Ion-Selective Electrodes. 2013https://doi.org/10.1016/B978-0-12-409547-2.01180-X
  59. Gastón A. Crespo, Eric Bakker. Dynamic electrochemistry with ionophore based ion-selective membranes. RSC Advances 2013, 3 (48) , 25461. https://doi.org/10.1039/c3ra43751e
  60. Gastón A. Crespo, Majid Ghahraman Afshar, Eric Bakker. Reversible Sensing of the Anticoagulant Heparin with Protamine Permselective Membranes. Angewandte Chemie 2012, 124 (50) , 12743-12746. https://doi.org/10.1002/ange.201207444
  61. Gastón A. Crespo, Majid Ghahraman Afshar, Eric Bakker. Reversible Sensing of the Anticoagulant Heparin with Protamine Permselective Membranes. Angewandte Chemie International Edition 2012, 51 (50) , 12575-12578. https://doi.org/10.1002/anie.201207444
  62. Claudio Zuliani, Dermot Diamond. Opportunities and challenges of using ion-selective electrodes in environmental monitoring and wearable sensors. Electrochimica Acta 2012, 84 , 29-34. https://doi.org/10.1016/j.electacta.2012.04.147
  63. Manzar Sohail, Roland De Marco, Krystina Lamb, Eric Bakker. Thin layer coulometric determination of nitrate in fresh waters. Analytica Chimica Acta 2012, 744 , 39-44. https://doi.org/10.1016/j.aca.2012.07.026
  64. Muhammad Tanzirul Alam, Manzar Sohail, Roland De Marco. Electrochemistry at the interface between an aqueous droplet and 1,2-dichloroethane. Electrochemistry Communications 2012, 19 , 142-144. https://doi.org/10.1016/j.elecom.2012.02.044
  65. Marcin Pawlak, Ewa Grygolowicz-Pawlak, Eric Bakker. Pulsed chronopotentiometric membrane electrodes based on plasticized poly(vinyl chloride) with covalently bound ferrocene functionalities as solid contact transducer. Pure and Applied Chemistry 2012, 84 (10) , 2045-2054. https://doi.org/10.1351/PAC-CON-11-09-23
  66. Gastón A. Crespo, Günter Mistlberger, Eric Bakker. Towards Ion‐Selective Membranes with Electrogenerated Chemiluminescence Detection: Visualizing Selective Ru(bpy) 3 2+ Transport Across a Plasticized Poly(vinyl chloride) Membrane. Electroanalysis 2012, 24 (1) , 61-68. https://doi.org/10.1002/elan.201100434
  67. Gastón A. Crespo, Eric Bakker. Ionophore-based ion optodes without a reference ion: electrogenerated chemiluminescence for potentiometric sensors. The Analyst 2012, 137 (21) , 4988. https://doi.org/10.1039/c2an35516g
  68. Ewa Grygolowicz-Pawlak, Eric Bakker. Thin layer coulometry ion sensing protocol with potassium-selective membrane electrodes. Electrochimica Acta 2011, 56 (28) , 10359-10363. https://doi.org/10.1016/j.electacta.2011.02.053
  69. Changming Cheng, Xianqing Tian, Yong Guo, Yi Li, Hongyan Yuan, Dan Xiao. Large enhancement of sensitivity and a wider working range of glass pH electrode with amperometric and potentiometric responses. Electrochimica Acta 2011, 56 (27) , 9883-9886. https://doi.org/10.1016/j.electacta.2011.08.065
  70. Gastón A. Crespo, Günter Mistlberger, Eric Bakker. Electrogenerated chemiluminescence triggered by electroseparation of Ru(bpy)32+ across a supported liquid membrane. Chemical Communications 2011, 47 (42) , 11644. https://doi.org/10.1039/c1cc14822b
  71. Sorin Kihara, Megumi Kasuno. Rapid and Precise Coulometric Determination and Separation of Redox Inert Ions Based on Electrolysis for Ion Transfer at the Aqueous|Organic Solution Interface. Analytical Sciences 2011, 27 (1) , 1-11. https://doi.org/10.2116/analsci.27.1
  72. Ewa Grygolowicz-Pawlak, Eric Bakker. Background current elimination in thin layer ion-selective membrane coulometry. Electrochemistry Communications 2010, 12 (9) , 1195-1198. https://doi.org/10.1016/j.elecom.2010.06.017
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Cite this: Anal. Chem. 2010, 82, 11, 4537–4542
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https://doi.org/10.1021/ac100524z
Published April 29, 2010

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  • Scheme 1

    Scheme 1. Schematic of the Thin Layer Ion-Selective Coulometric System Presented Here, Consisting of a Hollow Fiber Based Calcium-Selective Working Electrode, a High Surface Area Pt Counter Electrode, and a Double Junction Ag/AgCl Reference Electrode Immersed in 1 mM CaCl2 + 10 mM KCla
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    Scheme aThe working electrode is a 500 μm thick Ag/AgCl wire within the 600 μm i.d. polypropylene hollow fiber doped with 10 wt % ETH 500, 10 mmol·kg−1 Ca-ionophore IV, and 30 mol % (relative to the ionophore) of ion-exchanger KTFPB in DDNPE as a calcium-selective membrane. Sample solutions pass through the tubular electrode to form a thin sample layer (b) between the wire (a) and the membrane (c), while the wire is connected to the potentiostat at (d).

    Figure 1

    Figure 1. Potentiometric calibration curve for the hollow fiber based calcium-selective electrode with an inner thin layer sample solution ranging from 10−5 to 10−2 M CaCl2 in a 10 mM KCl background electrolyte. The outer solution is constant at 1 mM CaCl2 + 10 mM KCl. The straight line is the least-squares fit between logarithmic concentrations of −5 and −3, with a slope of 29.6 mV per 10-fold concentration change.

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    Figure 2

    Figure 2. Schematic presentation of the expected current−potential behavior of ion-exchanger based ion-selective membrane electrodes. The straight lines for the primary ion I+ and the background ion J+ are expected for high sample concentrations where sample depletion is negligible. The separation between the two lines is given by the membrane selectivity and the activity of the two ions. When mass transport of the primary ion in the aqueous phase becomes rate limiting, as with low concentrations or volumes, a limiting current that is linearly dependent on concentration is expected between the two straight lines that define the potential window.

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    Figure 3

    Figure 3. Normal pulse voltammograms obtained for a hollow fiber based system with an increased volume of inner sample solution (smaller diameter silver wire) containing varying concentrations of CaCl2 in a constant background of 10 mM KCl, while the outer solution consists of a constant 1 mM CaCl2 + 10 mM KCl. Note the concentration dependent limiting currents for this ion-exchanger based membrane system that compare to Figure 2.

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    Figure 4

    Figure 4. Chronoamperograms obtained for a thin layer (500 μm thick Ag/AgCl wire) coulometric system for samples of (A) 1 × 10−5 M, (B) 2.5 × 10−5 M, and (C) 5 × 10−5 M CaCl2 all in a 10 mM KCl background during various 30 s potential pulses vs open circuit potential, as indicated on the graph. Other conditions as in Figure 3.

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    Figure 5

    Figure 5. Calculated charge as a function of applied potential (A) vs open circuit potential and (B) vs Ag/AgCl wire for the calcium concentration indicated on the graphs. Other conditions as in Figure 4.

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    Figure 6

    Figure 6. Chronoamperograms of the thin layer system for the sample concentrations indicated on the graph (other conditions as in Figure 4). Here, the potential applied for individual concentrations was always 150 mV vs open circuit potential. The inset presents the calculated charge as a function of sample concentration from the chronoamperograms shown, confirming linear behavior.

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  • References

    This article references 32 other publications.

    1. 1
      Miller, R. L., Del Castillo, C. E., and McKee, B. A., Eds. Remote Sensing of Coastal Aquatic Environments. Technologies, Techniques and Applications; Springer: Secaucus, NJ, 2005.
      There is no corresponding record for this reference.
    2. 2
      Lee, H. J., Yoon, I. J., Yoo, C. L., Pyun, H.-J., Cha, G. S., and Nam, H. Anal. Chem. 2000, 72, 4694– 4699
      There is no corresponding record for this reference.
    3. 3
      Wang, J. and Tian, B. Anal. Chem. 1992, 64, 1706– 1709
      There is no corresponding record for this reference.
    4. 4
      Jacobs, E., Ancy, J. J., and Smith, M. Point Care: J. Near-Patient Test. Technol. 2002, 1, 135– 144
      There is no corresponding record for this reference.
    5. 5
      Bakker, E., Bhakthavatsalam, V., and Gemene, K. L. Talanta 2008, 75, 629– 635
      There is no corresponding record for this reference.
    6. 6
      Bard, A. J. Anal. Chem. 1966, 38, 88R– 98R
      There is no corresponding record for this reference.
    7. 7
      Oglesby, D. M., Anderson, L. B., McDuffie, B., and Reilley, C. N. Anal. Chem. 1965, 37, 1317– 1321
      There is no corresponding record for this reference.
    8. 8
      Tsujimura, S., Kojima, S., Ikeda, T., and Kano, K. Anal. Bioanal. Chem. 2006, 386, 645– 651
      8
      Potential-step coulometry of D-glucose using a novel FAD-dependent glucose dehydrogenase
      Tsujimura, Seiya; Kojima, Shinki; Ikeda, Tokuji; Kano, Kenji
      Analytical and Bioanalytical Chemistry (2006), 386 (3), 645-651CODEN: ABCNBP; ISSN:1618-2642. (Springer)
      This paper describes the construction and characterization of a batch-type coulometric system for the detection of D-glucose using a novel FAD-dependent glucose dehydrogenase. To overcome the problem of interferents, such as ascorbate and urate, a potential-step method was proposed to sep. the electrolysis reactions of interferents and D-glucose by selecting a mediator possessing an appropriate formal potential. The rapid oxidative consumption of the interferents proceeded in the first step, whereas the mediator and glucose remained reduced. In the second step, the mediator was immediately oxidized, and subsequent bioelectrocatalytic oxidn. of D-glucose occurred with the aid of aldose 1-epimerase. In this study, potassium octacyanomolybdate (IV) with a formal potential of 0.6 V vs. Ag|AgCl was chosen as a mediator, and the first and second electrolysis potentials were set at 0.4 V and 0.8 V, resp., by considering the heterogeneous electron-transfer kinetics and the potential window. The background-cor. response in charge corresponded to 99±2 % efficiency in terms of the amt. of D-glucose.
    9. 9
      Buhlmann, P., Pretsch, E., and Bakker, E. Chem. Rev. 1998, 98, 1593– 1687
      There is no corresponding record for this reference.
    10. 10
      Bakker, E., Buhlmann, P., and Pretsch, E. Chem. Rev. 1997, 97, 3083– 3132
      10
      Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 1. General Characteristics
      Bakker, Eric; Buehlmann, Philippe; Pretsch, Ernoe
      Chemical Reviews (Washington, D. C.) (1997), 97 (8), 3083-3132CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review, with 322 refs., is given on the relation of the response of carrier-based ion-selective electrodes and bulk optodes.
    11. 11
      Bakker, E. and Pretsch, E. Angew. Chem., Int. Ed. 2007, 46, 2– 11
      There is no corresponding record for this reference.
    12. 12
      Samec, Z., Samcova, E., and Girault, H. H. Talanta 2004, 63, 21– 32
      There is no corresponding record for this reference.
    13. 13
      Kim, Y. and Amemiya, S. Anal. Chem. 2008, 80, 6056– 6065
      13
      Stripping Analysis of Nanomolar Perchlorate in Drinking Water with a Voltammetric Ion-Selective Electrode Based on Thin-Layer Liquid Membrane
      Kim, Yushin; Amemiya, Shigeru
      Analytical Chemistry (Washington, DC, United States) (2008), 80 (15), 6056-6065CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      A highly sensitive anal. method is required to assess nano-molar perchlorate pollution in drinking water as an emerging environmental problem. A novel approach, based on a voltammetric ion-selective electrode for the electrochem. detection of redox-inactive perchlorate at a nano-molar concn. without its electrolysis was developed. The perchlorate-selective electrode is based on a sub-micrometer-thick, plasticized poly(vinyl chloride) membrane spin-coated on a poly(3-octylthiophene)-modified Au electrode. The liq. membrane serves as the first thin-layer cell for ion-transfer stripping voltammetry to give low detection limits of 0.2-0.5 nM perchlorate in deionized water, com. bottled water, and tap water under a rotating electrode configuration. Detection limits were much lower than the USEPA action limit (∼246 nM) and were comparable to detection limits of the most sensitive anal. methods for detecting perchlorate, i.e., ion chromatog. in conjunction with suppressed cond. detection (0.55 nM) or electro-spray ionization mass spectrometry (0.20-0.25 nM). Perchlorate mass transfer in the thin-layer liq. membrane and aq. sample and its transfer at the interface between the 2 phases were exptl. and theor. examd. to achieve the low detection limits. Advantages of ion-transfer stripping voltammetry with a thin-layer liq. membrane vs. traditional ion-selective potentiometry were demonstrated in terms of detection limit, response time, and selectivity.
    14. 14
      Jadhav, S., Meir, A. J., and Bakker, E. Electroanalysis 2000, 12, 1251– 1257
      There is no corresponding record for this reference.
    15. 15
      Shvarev, A. and Bakker, E. Anal. Chem. 2003, 75, 4541– 4550
      There is no corresponding record for this reference.
    16. 16
      Gemene, K. and Bakker, E. Anal. Chem. 2008, 80, 3743– 3750
      There is no corresponding record for this reference.
    17. 17
      Sanchez-Pedreno, C., Ortuno, J. A., and Hernandez, J. Anal. Chim. Acta 2002, 459, 11– 17
      There is no corresponding record for this reference.
    18. 18
      Sawada, S., Taguma, M., Kimoto, T., Hotta, H., and Osakai, T. Anal. Chem. 2002, 74, 1177– 1181
      There is no corresponding record for this reference.
    19. 19
      Yoshizumi, A., Uehara, A., Kasuno, M., Kitatsuhi, Y., Yoshida, Z., and Kihara, S. J. Electroanal. Chem. 2005, 581, 275– 283
      There is no corresponding record for this reference.
    20. 20
      Jadhav, S. and Bakker, E. Anal. Chem. 2001, 73, 80– 90
      There is no corresponding record for this reference.
    21. 21
      Jadhav, S. and Bakker, E. Anal. Chem. 1999, 71, 3657– 3664
      There is no corresponding record for this reference.
    22. 22
      Ueberfeld, J., Parthasarathy, N., Zbinden, H., Gisin, N., and Buffle, J. Anal. Chem. 2002, 74, 664– 670
      There is no corresponding record for this reference.
    23. 23
      Malon, A., Bakker, E., and Pretsch, E. Anal. Chem. 2007, 79, 632– 638
      There is no corresponding record for this reference.
    24. 24
      Oesch, U. and Simon, W. Anal. Chem. 1980, 52, 692– 700
      24
      Lifetime of neutral carrier based ion-selective liquid-membrane electrodes
      Oesch, Urs; Simon, Wilhelm
      Analytical Chemistry (1980), 52 (4), 692-700CODEN: ANCHAM; ISSN:0003-2700.
      Models for the estn. of the lifetime of neutral-carrier-based ion-selective liq.-membrane electrodes are presented. They are based on the kinetics of loss of plasticizer and/or ionophore from the solvent polymeric membrane phase into the sample soln. The exptl. obsd. lifetime is in good agreement with the theor. estd. value. For anal. relevant membrane systems, both the ion carrier and the plasticizer used should have partition coeffs. between sample and membrane larger than ∼106 to ensure a continuous-use lifetime of at least 1 yr.
    25. 25
      Telting-Diaz, M. and Bakker, E. Anal. Chem. 2002, 74, 5251– 5256
      There is no corresponding record for this reference.
    26. 26
      Anker, P., Ammann, D., Asper, R., Dohner, R. E., Simon, W., and Wieland, E. Anal. Chem. 1981, 53, 1970– 1974
      There is no corresponding record for this reference.
    27. 27
      Gehrig, P., Rusterholz, B., and Simon, W. Chimia 1989, 43, 377– 379
      There is no corresponding record for this reference.
    28. 28
      Bhakthavatsalam, V., Shvarev, A., and Bakker, E. Analyst 2006, 131, 895– 900
      There is no corresponding record for this reference.
    29. 29
      Qin, Y., Mi, Y., and Bakker, E. Anal. Chim. Acta 2000, 421, 207– 220
      29
      Determination of complex formation constants of 18 neutral alkali and alkaline earth metal ionophores in poly(vinyl chloride) sensing membranes plasticized with bis(2-ethylhexyl)sebacate and o-nitrophenyloctylether
      Qin, Y.; Mi, Y.; Bakker, E.
      Analytica Chimica Acta (2000), 421 (2), 207-220CODEN: ACACAM; ISSN:0003-2670. (Elsevier Science B.V.)
      A segmented sandwich membrane method is used to det. complex formation consts. of 18 elec. neutral ionophores in situ in solvent polymeric sensing membranes. These ionophores are commonly used in potentiometric and optical sensors, and knowledge of such binding information is important for ionophore and sensor design. In this method, two membrane segments are fused together, with only one contg. the ionophore, to give a concn.-polarized sandwich membrane. Unlike other approaches, this method does not require the use of a ref. ion in the sample and/or a 2nd ionophore in the membrane, and is typically pH insensitive. The following ionophores responsive for the common cations lithium, sodium, potassium, magnesium and calcium are characterized and discussed: valinomycin, BME-44, bis[(benzo-15-crown-5)-4'-ylmethyl]pimelate, ETH 157, ETH 2120, bis[(12-crown-4)methyl]dodecylmethylmalonate, 4-tert-butylcalix [4] arene tetraacetic acid tetra-Et ester, ETH 149, ETH 1644, ETH 1810, 6,6-dibenzyl-14-crown-4, N,N,N',N',N'',N''-hexacyclohexyl-4,4',4''-propylidyne tris(3-oxabutyramide), ETH 1117, ETH 4030, ETH 1001, ETH 129, ETH 5234, and A23187. The logarithmic complex formation consts. range from 4.4 to 29 and compare well to published data for ionophores that were characterized earlier. From the obsd. complex formation consts., max. possible selectivities are calcd. that would be expected if interfering ions show no binding affinity to the ionophore, and the values are compared with exptl. findings. Each ionophore is characterized in poly(vinyl chloride) membranes plasticized either with a polar (NPOE) or a nonpolar plasticizer (DOS). Membranes based on NPOE always show larger complex formation consts. of the embedded ionophore.
    30. 30
      Shvarev, A. and Bakker, E. Anal. Chem. 2005, 77, 5221– 5228
      30
      Response Characteristics of a Reversible Electrochemical Sensor for the Polyion Protamine
      Shvarev, Alexey; Bakker, Eric
      Analytical Chemistry (2005), 77 (16), 5221-5228CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      The authors describe here in detail the first reversible electrochem. sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the detn. of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequil. extn. of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extn. and ion stripping are now fully controlled electrochem. Spontaneous polyion extn. is avoided by using membranes contg. highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extn. of polyions is induced if a const. current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theor. response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochem. sensing system is characterized in terms of optimal working conditions, membrane compn., selectivity, and influence of sample stirring and org.-phase diffusion coeff. on the response characteristics. Excellent potential stability and reversibility of the sensors are obsd., and measurements of heparin concn. in whole blood samples via protamine titrn. are demonstrated.
    31. 31
      Bakker, E. and Meir, A. J. SIAM Rev. 2003, 45, 327– 344
      There is no corresponding record for this reference.
    32. 32
      Zook, J. M. and Lindner, E. Anal. Chem. 2009, 81, 5155– 5164
      There is no corresponding record for this reference.