Expanding the possibilities for an instrument-free method to reproducible resetting of the standard potential (E°) of solid-contact ion-selective electrodes

Abstract

Improving the reproducibility of the standard potential (E°) of solid-contact ion-selective electrodes (SC-ISEs) is of utmost importance on the way to simpler measurements with disposable sensors and sensors in locations where maintenance is challenging. In this work, an earlier introduced instrument-free method to reset the E° to a specific potential is developed by short-circuiting SC-ISEs with a solid-state Ag/AgCl quasi reference electrode (QRE) in a certain concentration of chloride and the primary ion of the SC-ISE. The short-circuiting method is evaluated for SC-ISEs based on poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs) as solid contacts, while a typical valinomycin-based spin-coated K+-selective membrane is used as a model ion-selective membrane. The capacitance of the Ag/AgCl QRE used in this work is orders of magnitude larger than the capacitance of the solid contact of the studied SC-ISEs. Therefore, upon short-circuiting, the potential of the QRE remains practically constant, while the potential of the SC-ISE is shifted until the potential difference between the SC-ISE and QRE approaches zero. When short-circuiting the SC-ISE with an Ag/AgCl QRE, the calibration curves can be shifted reversibly up and down on the potential axis in a reproducible and controlled manner. The calibration curve can be shifted by applying current pulse on SC-ISEs.