Article
Reference
Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion‐selective Electrodes
FORREST, Tara, ZDRACHEK, Elena, BAKKER, Eric
Abstract
The use of thin membrane layer ion‐selective electrodes (of ∼200 nm thickness) as rapid diagnosis tool is proposed. While conventional solid contact systems (with a membrane of
∼250 μm thickness) may exhibit a satisfactory stability for regular laboratory use, a signal degradation can still be distinguished over a longer period of time but this requires tedious and time consuming tests. By diminishing the thickness of the membrane by a factor of 103 approximately, diffusion processes happen faster, and the lifetime is significantly reduced.
This would ordinarily be a strong drawback but not if the aim is to detect a membrane deterioration in a shorter time frame. This characteristic makes thin membrane systems an ideal tool for rapid complications identification in the development process of conventional solid contact electrodes. The approach is demonstrated here in the development of an all new solid contact probe for anions. PEDOT−C14, a conducting polymer, was used for the first time in a solid contact electrode with an anion exchange membrane for the detection of nitrate. The thin layer configuration was used [...]
FORREST, Tara, ZDRACHEK, Elena, BAKKER, Eric. Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion‐selective Electrodes. Electroanalysis, 2020, vol. 32, no. 4, p. 799-804
DOI : 10.1002/elan.201900674
Available at:
http://archive-ouverte.unige.ch/unige:136739
Disclaimer: layout of this document may differ from the published version.
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Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion-Selective Electrodes
Tara Forresta, Elena Zdracheka and Eric Bakkera*
a Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland
* e-mail: eric.bakker@unige.ch
Received: ((will be filled in by the editorial staff)) Accepted: ((will be filled in by the editorial staff))
Abstract
The use of thin membrane layer ion selective electrodes (of ~200 nm thickness) as rapid diagnosis tool is proposed. While conventional solid contact systems (with a membrane of ~250 µm thickness) may exhibit a satisfactory stability for regular laboratory use, a signal degradation can still be distinguished over a longer period of time but this requires tedious and time consuming tests. By diminishing the thickness of the membrane by a factor of 103 approximately, diffusion processes happen faster, and the lifetime is significantly reduced. This would ordinarily be a strong drawback but not if the aim is to detect a membrane deterioration in a shorter time frame. This characteristic makes thin membrane systems an ideal tool for rapid complications identification in the development process of conventional solid contact electrodes. The approach is demonstrated here in the development of an all new solid contact probe for anions. PEDOT-C14, a conducting polymer, was used for the first time in a solid contact electrode with an anion exchange membrane for the detection of nitrate. The thin layer configuration was used to optimise the polymerisation parameters as well as the membrane composition without having to run week-long trials. A stable conventional solid contact electrode was in the end successfully developed and exhibited a lower detection limit of 10-5.5 M for nitrate with a stable Nernstian response for several days.
Keywords: Nitrate, PEDOT-C14, Ion-selective electrode, Thin membrane, Potentiometry DOI: 10.1002/elan.((will be filled in by the editorial staff))
1. Introduction
Over the past decade, solid contact ion selective electrodes (ISE) have become a standard analysis technique owing to the development of new ion-to- electron transducers. The principal motivations for the development of such sensors are the miniaturisation possibilities, which is more difficult with inner filling solution electrodes, increased stability, which is a problem faced with previously used coated-wire electrodes (CWE), robustness and low production costs. The conventional design of a solid contact electrode includes an electron conductor (gold, glassy carbon, platinum or others) covered by a transducing layer with on top the ion selective membrane, which is generally on the order of 200 µm thickness.
Conducting polymers (CP) are widely used transducers in the sensing field and include poly(3- octylthiophene) (POT) [1], poly(3,4- ethylenedioxythiophene) (PEDOT) [2], polypyrrole
(PPy) [3], polyaniline (PANI) [4] and many others.
They present some technical advantages, as they can be directly drop cast from solution onto the electrode or electropolymerised alongside another ion. Other examples of transducers have been reported in the literature such as carbon nanotubes [5], redox species [6] or gold nanoparticles [7].
Overall, many application examples for cations can be found but only a few report on anion sensing [1, 8]
with solid contact electrodes. As it was already previously demonstrated [9], an inadequate choice of transducing material has more drastic effects with anion sensors and is expressed by a poor long-term stability. As shown in reference [10], nitrate ion selective electrodes with POT and PANI as ion to electron transducer exhibited a larger drift over time than conventional liquid inner filling solution electrodes. A similar behaviour was reported for chloride selective electrodes with a polypyrrole
conducting film [11]. As the common goal is to generate a system that is the most stable over time, these effects are highly undesired. As of now, only sensors based on a transducing layer made out of functionalised multiwalled carbon nanotubes (f- MWCNTs) give good results in terms of stability and reproducibility [8, 12]. The transduction mechanism is in this case chiefly based on the capacitive behaviour of the carbon nanotubes rather than on the formation of a redox buffer like in conducting polymers.
Recently, a new family of PEDOT derivatives [13]
with superhydrophobic properties was synthesised and used as solid contact in ion selective electrodes.
Compared to the commonly used PEDOT, these derivatives prevent the accumulation of water at the membrane-polymer interface, which is an important source of drift. Cation selective electrodes (Na+, K+ and H+) with PEDOT-C14 as transducing layer have recently been reported in the literature [13] and exhibited a good response slope, EMF potential stability, and short equilibration time. These derivatives have also been reported in thin layer ion stripping voltammetry [14] but have not yet been used as transducers in anion selective electrodes and their applicability is not yet known.
Recently, the concept of thin layer potentiometry (membrane thickness around 200 nm) was introduced by our group [15]. It was demonstrated in this work that due to their small thickness, processes are indeed occurring faster and allow shorter preconditioning time and easier reconditioning properties. Although thinner membrane layers would appear to be less robust than conventional ion selective membranes, they open up new sensing possibilities. For example, sequential cation and anion sensing was achieved with a single electrode using the redox properties of the underlying POT layer [15]. In this same study, thin layer systems exhibited similar performances as conventional systems when analysing cations, but the response was less stable for the anion response. This was mainly attributed to the fact that POT was used as a transducer and is known for its poor stability in its oxidised form [16].
In view of these results, it seemed reasonable at that point to try to replace the inadequate POT with another conducting polymer, PEDOT-C14.
The synthesis procedure of PEDOT-C14 presents several advantages such as electrochemical deposition and ion incorporation in the film. Like many other conducting polymers, PEDOT derivatives can be either positively charged or neutral, leading to diverse properties. Previous studies with PEDOT as ion-to-
electron transducer have reported successful synthesis protocols using PSS- [2], Cl- [2], ClO4- [17], PF6- [17]
and TPFPB- (tetrakis(pentafluorophenyl)borate) [13, 14] as counter-anions.
As in potentiometry, the goal is to have a stable signal baseline, undesired ion exchange between the transducing layer and sensing film should be avoided.
Due to their higher hydrophilicity and mobility, small anions were therefore not considered as appropriate candidates in this case. Although NaPSS has often been used as supporting electrolyte in the synthesis of PEDOT, it seemed less appropriate for this application due to the possibility of forming a water layer at the transducer/membrane interface. Such water layers have been extensively reported in the literature and are known to induce drift over time in potentiometric measurements [13]. For stable and long term use potentiometric probes, the combination of PEDOT-C14
and a bulky hydrophobic anion (TPFPB-) seemed promising.
In order to design a system with a lifetime as long as possible, which is required in the environmental field for example, stability studies are part of the routine procedure but are often time consuming and can last up to months to gather the necessary information. We report here on the use of a thin membrane system to allow a more rapid identification of possible issues (e.g. leaching of components, drift and inter-electrode reproducibility) to design a new conventional solid contact setup optimised for anion sensing. By taking advantage of the fast processes happening within the thin membrane, the influence of the conducting polymer on the final signal was studied in a reduced time frame. The parameters optimised thank to the thin membrane system will be in the end applied to a conventional solid contact electrode to generate a stable sensor without having had to run time consuming experiments.
To our knowledge, PEDOT-C14 is used here successfully for the first time as solid contact transducer in an anion sensing probe.
2. Experimental
2.1. Reagents, Materials and Equipment
All aqueous solutions were prepared in deionized water (>18 MΩ cm). Sodium nitrate (≥99.0%, NaNO3), polyurethane (SelectophoreTM, PU), bis(2-ethylhexyl) sebacate (≥97.0%, DOS), tridodecylmethylammonium nitrate (≥99.0%, TDMAN) and tetrahydrofuran (≥99.5%,
SelectophoreTM, THF) were purchased from Sigma- Aldrich. Potassium tetrakis(pentafluorophenyl)borate (≥97%, KTPFPB) was purchased from Alfa Aesar and analytical grade acetonitrile (≥99.5%, ACN) from Fischer Scientific. EDOT-C14 was synthesised in house according to the reference [13].
2.2. Electrode preparation and electrochemical equipment
Glassy carbon (GC) electrodes from Metrohm (Ø 3.00 ± 0.05 mm, body diameter 10.00 ± 0.05 mm) were polished using different diamond powder suspensions (Ø 6-3-1- 0.25 µM) prior to use. Electropolymerisation of the transducing layer was performed in a three electrodes system with a PGSTSAT 128N (Metrohm Autolab, B.V., Utrecht, The Netherlands) controlled by the Nova 1.8 software. A platinum electrode was used as a quasi- reference with a glassy carbon rod as counter electrode.
All potentiometric measurements were performed using a high impedance input 16-channels EMF monitor (Lawson Laboratories, Inc., Malvern, PA) to record the signal with a double-junction Ag/AgCl/ 3 M KCl/ 1 M LiOAc (Metrohm, Switzerland) as reference electrode.
All measurements were carried out in a Faraday cage to prevent unwanted noise.
The thin membrane coating was performed by drop casting 25 µL of membrane cocktail on top of the electrode in a spin coating apparatus (Lab Spin, Süss Microtech) at a speed of 1500 rpm [18]. The electrode was held by a custom-made chuck with a 10P7 hole of 3 mm ± 0.1 mm depth under vacuum. During the deposition, the electrode was rotated for 120 s to allow a thin membrane to be formed. The thickness estimation of the membrane (200 nm) was based on previous work done in our group with the same methodology [19].
2.3. Preparation of the Electrodes
The polymerisation solution used to generate the transducing layer was made of 0.03 M of KTPFPB and 0.01 M of EDOT-C14 in acetonitrile as suggested in reference [13]. The PEDOT-C14 films were generated on the clean GC electrode by dynamic electropolymerisation (cyclic voltammetry), starting at a negative potential and stopping at a positive one to integrate a portion of counter-anion into the film. The electrodes were soaked overnight in acetonitrile to remove any unbound compounds and then dried in the air for two hours.
The thin membrane cocktail was prepared by dissolving 12.488 mg of PU, 12.892 mg of DOS, 0.62 mg of TDMAN (40.0 mmol/kg) and 0.09 mg (5.0 mmol/kg) of KTPFPB in THF. The spin coating was performed as specified above. PU was in this case preferred to PVC because of increased robustness with thin layer membranes as proven by previous work conducted in our group [20].
The thick membrane cocktail was prepared by dissolving 47.82 mg of PU, 49.38 mg of DOS, 2.4 mg of TDMAN (40.06 mmol/kg) and 0.36 mg of KTPFPB (5.02 mmol/kg) in 1 mL THF. A total amount of 150 µL (3 times 50 µL) of membrane cocktail was drop cast onto the electrode body and left to dry overnight.
Both membrane cocktails were prepared with matching concentrations to allow comparison.
Prior to analysis, all electrodes were conditioned in 1 mM of corresponding salt. Thicker membranes were always conditioned overnight and thinner ones in 1-2 hours.
3. Results and Discussion
In a first step, different polymer films were synthesised using a dynamic electropolymerisation process (cyclic voltammetry). The potential was always scanned from negative to positive (-0.85 V to 1.4 V vs Pt pseudo-reference) and the process was stopped at a positive potential to generate a partially charged polymer. This was performed to integrate a portion of the counter anion into the film (PEDOT- C14+-TPFPB-). The growth of the polymer onto the substrate was evaluated by a rising peak for consecutive cycles located at around -0.1 V (Figure 1).
The potential at which the electropolymerisation process was stopped suggested to have no influence on the potentiometric performances. It was seen that as long as it was after the polymer oxidation peak an equilibrium between the charged and neutral form of PEDOT-C14 is occurring – Figures in supporting information. Different polymerisation supporting electrolytes (other boron derivatives) were tested and are also presented in the supporting information. In the case where the polymerisation was not occurring the stability of the supporting electrolyte in the corresponding electrochemical window was tested (Figure 4S).
After polymerisation, the electrodes were prepared as mentioned in the experimental part and their performance was evaluated in potentiometry. With the thin membrane setup, only three days were needed at maximum to evaluate the performance of the system.
Structural studies on PEDOT and PEDOT derivatives have shown that a higher upper polymerisation potential (overoxidation) induces some structural changes in the crystalline arrangement of the polymer [21]. Although overoxidation might seem unsatisfactory, it has been proven to be beneficial in some applications, such as biosensors [22]. It was therefore interesting to compare these two types of polymer regarding their performance as solid contact transducers. To generate an overoxidised PEDOT-C14, the upper oxidation potential was pushed higher until the appearance of a single peak (with no corresponding backwards peak), which is commonly seen in this case (Figure 2).
Fig. 1. Cyclic voltammetry polymerisation of EDOT-C14 10mM with KTPFPB 30mM in ACN. 2.5 cycles, n=100 mVs-1, -0.85V – 1.2V vs Pt, stop at 0.6V.
Both electrodes generated with the two different polymers were prepared the same way and a thin membrane was applied onto the transducing layer to test the potentiometric behaviour. One important advantage of thin membrane systems over conventional systems is that the preconditioning time required before the measurements can be reduced to one hour compared to overnight conditioning.
Fig. 3. Cyclic voltammetry polymerisation of EDOT-C14 10mM with KTPFPB 30mM in ACN. 2.5 cycles, n=100mVs-1, -0.85V – 1.6V vs Pt, stop at 0.6V.
This allows one to condition and test electrodes on the same day. Figure 3 shows the different potentiometric response over three days for the two types of polymers that were generated. As it can be seen in Figure 3a), the electrode fabricated with the lower polymerisation potential (Figure 1) shows a lower stability and reproducibility in terms of Nernstian slope (3.2 mVdec-1). Even though the drift of E0 value is not catastrophic (~11.7 mV per day), its deviation afar from the Nernstian ideal behaviour makes it difficult to be reliable.
Figure 3b shows the potentiometric response for the second type of electrodes with the higher polymerisation potential (Figure 2). As it can be seen in this case, the response slope is very stable (0.2 mVdec-1) and always close to the ideal Nernstian behaviour. Although the E0 value drifted slightly more than in the previous attempt (~26.5 mV per day), the results prove to be more reliable with this approach and also yielded a better and more stable detection limit of 10-5.5 M over the whole testing period. The scan rate dependency versus the peak height was tested
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Fig. 2. a) Potentiometric response to nitrate over 3 days for the system with the lower polymerisation potential. b) Potentiometric response to nitrate over 3 days for the system with the higher polymerisation potential. c) Peak height and scan rate dependency to confirm the thin membrane behaviour. n=100mVs-1 in 1mM NaNO3, ref= Ag/AgCl/3 M KCl/1 M LiOAc and counter=Pt wire.
White trace is the forward peak and blue trace is the backwards peak. Error bars are standard deviations (n=3)
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yDay1= 83.8 ± 9.9 - 54.1 x yDay2= 47.3 ± 5.1 - 54.6 x yDay3= 30.9 ± 3.3 - 54.6 x
a) c)
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/µ
R2 = 0.998
R2 = 0.997
yDay1= 75.7 ± 11.3 - 50.3 x yDay2= 52.6 ± 5.4 - 46.1 x yDay3= 67.7 ± 0.6 - 43.9 x
< <
for these electrodes to confirm thin layer behaviour (Figure 3c). With thin membranes, diffusion processes are no longer relevant and the peak current is linearly dependent with the scan rate [23].
It was deducted at that stage that the drift of the E0 value was caused by the PEDOT-C14/PEDOT-C14+
transformation. Once the membrane is cast on the electrode, if a small portion of PEDOT-C14+ is reduced, it will automatically liberate its counter anion TPFPB-. As this anion is of lipophilic nature, it will be extracted into the membrane and will start to pair with the anion exchanger, thus changing its available concentration for measurement. This effect is stronger with thinner membranes since there is evidently a lower amount of TDMAN.
In order to generate the most stable system possible, two other parameters were evaluated. A first experiment was performed by varying the polymer layer thickness onto the surface of the electrode. As demonstrated by Faraday’s law, the total charge passed through a system is correlated to the generated mass.
Thus by modulating the charge during the electropolymerisation process, the thickness of the polymer can be modified. Previous results already showed that the thickness of a conducting polymer film is increasing linearly with the number of applied polymerisation cycles [18]. In this case, a thinner and a thicker transducer layer were tested by using 1.5 cycles and 3.5 cycles of polymerisation in contrast with the 2.5 cycles that were commonly used in previous experiments. Figure 4a shows the initial potentiometric response of three different electrodes. Although the responses may seem similar, several conclusions can be drawn from this experiment. The thicker polymer layer stabilises the system by improving the reproducibility from electrode to electrode between consecutives calibrations but also shrinks the response range, which makes it less convenient. With the thinner membrane, even though it exhibited the best initial response, it was seen that it suffered from a smaller inter-electrode reproducibility (11.8 mV). As a result, the intermediate polymer layer thickness (2.5 cycles) showed overall the best results in terms of stability over time, drift and response range.
The second parameter that was tested was the concentration of KTPFPB in the membrane cocktail.
As mentioned previously, the transducing layer is electropolymerised with KTPFPB as supporting electrolyte, therefore TPFPB- anions are included in the film to maintain electroneutrality with PEDOT- C14+. To improve the stability at the transducer – membrane interface a small portion of this same anion was included inside the membrane. This was realised in order to reduce the drift emanating from the TPFPB-
flux between the membrane and the transducing polymer. As shown in Figure 4b, three electrodes were prepared with different concentrations of cation exchanger in the membrane to find the adequate membrane composition. As expected, the membrane cocktail prepared with no KTPFPB was less reproducible (variation of 11.3 mV between each replicate). The best results were achieved with the membrane containing 5 mmol/kg of KTPFPB with a value close to 7.0 mV. A larger variability makes the measurements less reliable, and thus not optimal.
Fig. 4. a) Potentiometric response to nitrate for different electrodes with increasing transducing layer thickness. b) Potentiometric response with different concentration of KTPFPB in the membrane cocktail. Error bars are standard deviations (n=3). All electrodes were polymerised by cyclic voltammetry of EDOT-C14 10mM with KTPFPB 30mM in ACN. 2.5 cycles, n=100mVs-1, -0.85V – 1.6V vs Pt, stop at 0.6V.
This observation demonstrates the benefit of including a small portion of supporting anion in the film for increased response stability. From this experiment, it was also shown that a higher concentration of KTPFPB in the membrane (10 mmol/kg) did not seem to help achieve a better response as the slope value was
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y1.5 cycles= 79.4 ± 11.8 - 52.2 x y2.5 cycles= 90.8 ± 8.1 - 51.3 x y3.5 cycles= 162.0 ± 8.0 - 51.8 x
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b)
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y10mmol/kg KTPFPB= 82.1 ± 8.1 - 49.8 x y5mmol/kg KTPFPB= 90.8 ± 7.0 - 51.3 x yNo KTPFPB= 102.9 ± 11.3 - 51.8 x
worse and the reproducibility (8.1 mV) was not improved compared to the electrode with the membrane containing 5 mmol/kg of KTPFPB.
The tests for the membrane and the transducer thickness optimisation were realised in two days, one for the polymer deposition and one for the membrane deposition, conditioning and testing. This experimental timeframe is significantly shorter than with thicker membrane systems as the conditioning in this case only takes 1-2 hours compared to a full day. Because of the reduced thickness of the membrane, a high sensitivity to parameter changes can be noticed resulting in a shorter experimental time needed to draw useful conclusions.
In a last step, these optimised polymerisation conditions and membrane composition were applied to a conventional solid contact setup with a membrane of
~250 µm (as measured with a calliper). To underline the advantage of using thinner membranes to emphasise possible issues in these sensing systems, other electrodes with un-optimised conditions were also prepared to allow comparison. As the membrane is now a thousand times thicker than the one used for the optimisation process, stability and drift issues are expected to be less obviously seen.
Fig. 5. Cyclic voltammograms. Polymerisation with EDOT-C14
10mM and KTPFPB 30mM in ACN. 2.5 cycles, n=100mVs-1, a) -1.15V – 1.1V vs Pt, stop at 0.5V. b) -1.15V – 1.25V vs Pt, stop at 0.5V. c) Potentiometric response to nitrate over 3 days for the system with the lower polymerisation potential. d) Potentiometric response to nitrate over 3 days for the system with the higher polymerisation potential. Error bars are standard deviations (n=3).
As shown in Figure 5a and 5b, two different polymerisation processes were used to generated two types of transducing layers. It is important to state that
the upper and lower vertex potentials used during the electropolymerisation have shifted compared to the ones previously used in the thin membrane setup. This is mainly due to the fact that a platinum pseudo- reference was used and potential shifts can often be noticed in this case. The principal goal here was to have one case without the second peak (Figure 5a) and one with it (Figure 5b) to perform the same comparison as previously done with thin membranes.
This shift in the polymerisation window was also reverberated on the stop potential.
With thin membranes, these two systems had a clear different behaviour over time as seen when comparing Figure 3a and 3b. As expected, because the experiment was performed over ten days, no great differences can be seen between the two systems (Figure 4c and 4d) and the degradation of the signal for the un-optimised system was never reached.
The results also clearly show similarities with the thin membrane setup such as the initial potential drop after the first exposure. It can be seen that the E0 shift was assessed in one day with the thin membrane setup but here took five days to exhibit the same trend. The cause for this initial potential drop is yet unidentified.
Apart from this shift, the final response to nitrate for the developed sensor remained stable for more than ten days. The stability of the Nernstian slope was very satisfactory with a standard deviation of less than 0.01 mV dec-1 per day between day 5 and 10. After an initial exposure drop, the E0 value remained very stable during the whole testing period with a standard deviation of 0.45 mV per day.
4. Conclusion
It was demonstrated in this work that thin membrane systems can successfully be used as fast development tool in the fabrication process of new sensors. A new combination of the conductive polymer PEDOT-C14
with an anion exchange membrane allowed the detection of nitrate ions in water with a solid contact electrode. By reducing the thickness of the membrane, diffusional processes happen at a faster rate, thus significantly shortening the experimental time needed to get stability data. Simple optimisation tests can be performed in a couple of days, allowing for a more rapid optimisation process when developing a new sensing tool. Comparison with regular systems allowed us to underline the benefits of using thin membrane layer in the preliminary tests to avoid time-consuming experiments. It was shown that lifetime experiments that give inconclusive results after a week of testing
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yDay 10= 13.1 ± 1.2 - 53.4 x yDay 5= 17.1 ± 0.5 – 53.7 x yDay 1= 51.5 ± 1.3 - 54.0 x
yDay 10= 7.4 ± 0.6 - 53.7 x yDay 5= 13.6 ± 0.3 – 53.8 x yDay 1= 51.3 ± 1.1 - 54.1 x
a) b)
c) d)
with a conventional setup can be mirrored with thinner membrane and performed within a couple of days.
Acknowledgments
The authors thank the Eurostars AQISE Project (Agreement no. 2155004828) for funding of this work.
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Thin Layer Membrane Systems as Fast Development Tool for Potentiometric Solid Contact Ion-Selective Electrodes
Tara Forresta, Elena Zdracheka and Eric Bakkera*
a Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva, Switzerland
* e-mail: eric.bakker@unige.ch
Fig. 1S Cyclic voltammetry polymerisation of EDOT-C14 10mM with KTPFPB 30mM in ACN. 2.5 cycles, ref=Pt electrode and counter = GC rod, n=100 mVs-1. a) Stop potential at 1.6V. b) Stop potential at 1.4V. c) Stop potential at 1.1V. d) Stop potential at 0.8V.
Fig. 2S a) Potentiometric response to nitrate for all the electrodes with the different stop potential of the polymerisation process (see Figure 1S). b) Potentiometric response to nitrate over 2 days for the system with the lower stop potential (0.8V). Error bars are standard deviations from separate electrodes (n=3).
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a) b)
c) d)
y1.1V= 91.0 - 53.7 x y0.8V= 92.2 – 55.0 x y1.6V= 106.9 - 54.4 x
y1.4V= 88.1 - 53.7 x
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yDay 2= 54.8 - 55.3 x yDay 1= 92.2 - 55.0 x
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a) b)
Fig. 3S Cyclic voltammetry polymerisation with different supporting electrolytes. 5 cycles were applied to have clear evidence of polymerisation process. In all cases the reference electrode was a Pt electrode and the counter electrode a GC rod. The scan rate was n=100 mVs-1 a) Polymerisation of EDOT-C14 10mM with KTPhB 0.1M in ACN b) Polymerisation with EDOT-C14 10mM and ETH500 30mM in ACN c) Polymerisation with EDOT-C14 10mM and TBAPF6 0.1M in ACN d) Polymerisation with EDOT-C14 10mM and TBAClO4 0.1M. The polymerisation was only successful in c) and d).
Fig. 4S Cyclic voltammetry of supporting electrolyte only. 5 cycles were applied to have clear evidence of possible degradation processes. A solution of ETH500 30mM in CAN was used. The reference electrode was a Pt electrode and the counter electrode a GC rod. The scan rate was n=100 mVs-1
No clear evidence of degradation was seen with ETH500 (Figure 4S) and the absence of a growing polymer film (Figure 3Sb) with this supporting electrolyte cannot yet be explained. Evidence of electrochemical degradation (data not shown) was observed for KTPhB that may explain the absence of polymer formation.
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c) d)
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