Selectivity problems of membrane ion-selective electrodes - A method alternative to the IUPAC recommendation and its application to the selectivity mechanism investigation

A brief review of problems related to the determination of selectivity coef ficients of ion-selective electrodes and their interpretation is given, alo ng 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 prop osed permits the determination of the electrode selectivity as a function d ependent 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 we re interpreted as a result of the process of ion adsorption at the interfac e between the electrode membrane and the solution studied. The experimental evidence supports the conclusions from the studies of Pungor et al., who c laimed that processes at this interface play the main role in the mechanism of generation of the potential of ion-selective electrodes.