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Technical and fundamental possibilities and limitations of constant potential coulometry with ion-selective electrodes
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DOI：10.1016/j.jelechem.2026.120165.png)
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Abstract
En 中文
Constant potential coulometry method of measuring with ion-selective electrodes (ISEs) invented by Prof. Bobacka in 2015 looks promising for analytical purposes due to increased sensitivity (compared to potentiometry), however coulometric transduction remains understudied in some fundamental respects. Here we study (i) whether it is justifiable to use the Nernst equation to interpret the results obtained for ISEs in chronoamperometric/coulometric mode, (ii) what determines sensitivity and reliability of the results, (iii) how to improve the latter. Electrochemical impedance spectroscopy allowed us to conclude that standard exchange current density at the interface between Ca2+-selective membrane and aqueous solution significantly exceeds currents used in constant potential coulometry method (like shown earlier for K+ Li+ and Na+ ISEs). This means that the local electrochemical equilibrium at this interface is not violated by flowing current and thus the Nernst equation is applicable for the interpretation of results obtained. The study has shown that ultimately, the sensitivity and accuracy of constant potential coulometry is determined precisely by how accurately we measure and set the potential, i.e. by the same factors which determine the sensitivity of potentiometry. In this work, however, we propose two novel protocols of chronoamperometric/coulometric measurements with ISEs which allow to enhance reliability of the results obtained. The first provides recording several signals (twin peaks) instead of only one from the same sample, the second allows obtaining several calibrations with only one set of calibration solutions. Importantly, these protocols are technically straightforward, requiring a commercially available potentiostat without additional hardware or circuitry.
Keywords:
Ion-selective electrodes
Chronoamperometry
Constant potential coulometry
Potentiometry
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4.1
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1.7W
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