Resolution increase of ion-selective electrodes response by using a reversed amperometric setup

Typical ion-selective electrodes (ISEs) used in potentiometric mode suffer from low sensitivity, determined by Nernst (Nikolsky-Eisenman) equation. This limits resolution of potentiometric analysis, ultimately leading to significant problems in determination of relatively small changes of analyte ions concentration. A novel method was proposed using a ‘reversed’ amperometric setup with Ag|AgCl electrode as the working electrode and an ion-selective electrode as the reference one. Advantageously, the proposed approach does not require addition of other chemicals to the sample. A change of primary ions concentration results in change of the potential of the ISE used as the reference electrode and thus in the same change of Ag|AgCl electrode potential in amperometric (potentiostatic) mode. Due to high slope of the current vs. potential dependence for silver / silver chloride electrode small changes of ISE potential will result in significant changes of the recorded current, leading to high amplification of the analytical signal towards primary ions of the ISE. Additional unique advantage of herein proposed approach is a linear dependence of the current on analyte concentration, as tested on model examples of potassium- and calcium-selective ISEs.