THE STUDY OF PROCESSES INFLUENCING APPARENT SELECTIVITY FOR SOLID STATE ION-SELECTIVE ELECTRODES

Abstract

The Nikolsky equation, which is most commonly used for describing the potential response of ion-selective electrodes is perfectly valid only in an ideal system. One of the indications that other processes must also take part in the response of solid-state ion-selective electrodes is the discrepancy between the experimentally measured selectivity coefficients and the possibilities of analytical measurements. The processes which influence the electrode response and which are not predicted by the Nikolsky equation are the intrinsic solubility of the membrane, adsorption and redox processes and contamination of the solution by the main and interfering ions. If all those effects are taken into account they can be eliminated by a proper choice of measuring conditions and the measured selectivity coefficients approach their values predicted on the basis of thermodynamic data and give a sound basis for estimating the possibility of interferences in analytical measurements. In this paper selectivity coefficients for silver and copper electrodes were evaluated for nickel, cobalt, manganese, zinc, cadmium and lead as interfering ions.