Selectivity problems of membrane ion-selective electrodes

Abstract

A brief review of problems related to the determination of selectivity coefficients of ion-selective electrodes and their interpretation is given, along with a short critical description of the so far applied methods of their determination. A new method is proposed, the experimental part is similar to the mixed solution method recommended by IUPAC but avoids its drawbacks and can be used in cases when the latter cannot be applied. The method proposed permits the determination of the electrode selectivity as a function dependent on the activity of the ions studied, permitting conclusions on the mechanisms of the potential formation and selectivity. The performance of the method is illustrated for a nitrate electrode. Significant dependencies of the selectivity coefficients on concentration of the disturbing ions were interpreted as a result of the process of ion adsorption at the interface between the electrode membrane and the solution studied. The experimental evidence supports the conclusions from the studies of Pungor et al., who claimed that processes at this interface play the main role in the mechanism of generation of the potential of ion-selective electrodes.