Determination of Selectivity Coefficients of Ion-Selective Microelectrodes

Abstract

The application of an ion-selective microelectrode to measurements of ion activities requires a determination of its selectivity coefficient, i.e. the ability of a given ion-selective microelectrode to distinguish between the primary ion and the interfering ion. For the measurements of intracellular Na, Ca, Cl, and extracellular K ion activities, it is necessary to determine accurately the selectivity coefficient of each microelectrode because interfering ion activities are much greater than the primary ion activities. In this study we have attempted to evaluate the methods used usually for determining the selectivity coefficients as well as a method modified from others. For this evaluation, selectivity coefficients of recessed-tip and protruded-tip Na⁺-selective glass microelectrodes were determined by the various methods and examined.