Instrument-Free Control of the Standard Potential of Potentiometric Solid-Contact Ion-Selective Electrodes by Short-Circuiting with a Conventional Reference Electrode

A simple, instrument-free method to control the standard potential (E degrees) of potentiometric solid-contact ion-selective electrodes (SC-ISE) is described. In this method, the electrode potential of a SC-ISE is reset by short-circuiting the electrode with a metallic wire to a conventional Ag/AgCl/3 M KCl reference electrode (RE) in a solution containing primary ions. The method is studied experimentally for SC-ISEs where the conducting polymer poly(3,4-ethylenedioxythiophene) doped with the bulky anion poly(sodium 4-styrenesulfonate), PEDOT(PSS), is used as the solid contact. Three different types of ion-selective membranes (ISMs) are studied: two potassium-selective membranes, with and without the lipohilic additive tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH-500) and a cation-sensitive membrane without an ionophore. When the SC-ISE is short-circuited with the RE, the PEDOT(PSS) layer is oxidized or reduced, thereby shifting the potential of the SC-ISE to the proximity of the potential of the RE so that the potential difference between these two electrodes becomes zero or close to zero. The slope of the calibration curve is preserved after the short-circuit treatment of the SC-ISEs. The short-circuiting method is an important step toward calibration-free potentiometric analysis.