Potentiometric selectivity coefficients: Problems of experimental determination

The main problems arising in the determination of selectivity coefficients of ion-selective electrodes using the methods recommended by IUPAC are considered. A method for the determination of the limiting (thermodynamically justified) selectivity coefficients based on the analysis of the time dependence of the selectivity coefficients found experimentally using the separate solutions method is justified theoretically and experimentally. It has been demonstrated that the proposed method ensures the reliable determination of low values of selectivity coefficients (as low as n × 10^?6). The criteria of the applicability of the proposed method are formulated and a particular algorithm of its implementation is proposed.