Perspective on the coulometric transduction principle for ion-selective electrodes

A new type of coulometric transduction method for solid-contact ion-selective electrodes was introduced in 2015. The coulometric method utilized the capacitance of the solid contact to convert a potential change into a current transient that was integrated to obtain the corresponding charge. For a given potential change, the charge was increased by increasing the capacitance of the solid contact, which improved the sensitivity of solid-contact ion-selective electrodes. By introducing an electronic capacitor in series with the ion-selective electrode (ISE), the coulometric method became faster and feasible also for conventional ISEs with an internal filling solution. Alternative electrode configurations, where the ISE was connected as the reference electrode in the electrochemical cell, was used to avoid polarization of the ISE during the coulometric readout. Results published so far indicate that the coulometric readout method can significantly improve the analytical performance of ISEs, especially for detection of very small changes in ion activity. In this perspective article, the coulometric transduction method is revisited and critically evaluated.