ABSTRACT
A longstanding need for a reliable monitor of calcium ion activities in medicine and the life sciences was fulfilled in 1967 by a calcium ion-selective electrode based on a liquid membrane of calcium didecylphosphate sensor dissolved in dioctylphenyiphos- phonate solvent mediator. It is relatively easy to convert a liquid ion exchanger to an alternative ionic form. However, the success of the resultant electrode occasionally depends on how the exchanger is formulated. There is much speculation on the relative roles of sensors and mediators in the conventional liquid ion-exchanger membrane electrodes. Thus, the selective sensing qualifies of liquid ion exchangers in electrode membranes are attributed to the greater selectivity of these exchangers for counter-ions compared with resinous ion exchangers. For discrimination among cations within a given group of the periodic system, the influence of the solvent/mediator with neutral carrier sensors is considered of minor importance.
