Novel design of a planar flow-through potentiometric sensor

A novel planar electrode for flow-through potentiometric sensing is presented in this work. Planar and concentric potassium solid-contact ion-selective electrodes (K+-SCISEs) were designed and studied using potentiometry and electrochemical impedance spectroscopy (EIS). The K+-SCISE consisted of a neutral carrier PVC-based ion-selective membrane with valinomycin as ionophore, carbon cloth as ion-to-electron transducer, and a gold wire as electronic conductor, all incased in a polycarbonate support. The prepared electrodes showed a stable and reproducible potentiometric response. The average slopes for three identical flow-through K+-SCISEs, calibrated once per day during five days (n = 15), was 57.2 mV/decade (SD = 0.9 mV/decade). The corresponding standard potential of the electrodes during five days (n = 15) was 417 mV (SD = 3.6 mV). The water-layer test showed that the ion-selective membrane/carbon cloth interface was not subject to the formation of a water layer. The electrodes had selectivity coefficients comparable to the values obtained from the literature. The resistance of the ion-selective membrane, determined by EIS, was in the range of 45–250 MΩ for the planar electrode geometries studied in this work.