Selectivity of carrier-based ion-selective electrodes: Is the problem solved?

Traditional experimental and theoretical tools to describe the selectivity behavior of solvent polymeric membrane ion-selective electrodes are in many cases inadequate. Even in ideal situations, the generally applied Nicolskii-Eisenman equation is often not applicable. Moreover, real-world ion-selective electrodes often show non-ideal behavior, thus questioning the usefulness of reporting Nicolskii coefficients as a measure of selectivity. Bra recent years, a number of reports have aimed ae resolving these issues. Empirical methods such as the matched potential method have emerged as additional tools to characterize the apparent selectivity the real-world samples, unrestricted by theoretical assumptions, On the other hand, a number of experimental procedures are now available to determine the relevant ion-exchange selectivity of potentiometric membranes. New formalisms have been reported recently to describe the mixed ion response of ion-selective electrodes, which is incorrectly described by the Nicolskii-Eisenman equation, These recent efforts are discussed and compared In view of their practical significance.