Electrochemical Behavior and Analytical Applications of the Ion-Selective Electrodes Based on Oil/Water Interface

Abstract

Electrochemical studies on the ion transfer across the interface between immiscible organic and aqueous electrolyte solutions (oil/water interface) indicate that an oil/water interface works satisfactorily as an ion-selective electrode interface for both amperometric (or voltammetric)and potentiometric analyses of ions. The presence of an ionophore, which specifically binds an ion in the oil phase, renders the interface ion-selective for the ion. This was experimentally demonstrated for the transfer of sodium, potassium, rubidium, cesium, and ammonium ions across the ionophore(L)-containing nitrobenzene/water interface, where L is dibenzo-18-crown-6 (DB 18 C 6), and of sodium and potassium ions across the Lcontaining nitrobenzene/water interface, where L is bis[(benzo-15-crown-5)-4'-ylmethyl]pimerate (BB 15 C 5), DB 18 C 6, dibenzo-24-crown-8 (DB 24 C 8), or dicyclohexano-18--crown-6(DC 18 C 6, isomeric mixture). Theoretical and experimental examinations show that the ion-selective oil/water interface permits two types of electrochemical analyses of ions: amperometry (or voltammetry) and potentiometry. In other words, the oil/water interface can function either as an amperometric (or voltammetric) ion-selective electrode or as a potentiometric ion-selective electrode. The former gives the current response proportional to the concentration of ion, whereas the latter the potential response linear to the logarithm of ion activity (concentration). An advantage of the voltammetric method over the potentiometic one is that two or more ions can be simultaneously determined if their half-wave potentials are reasonably separated. This was experimentally verified for simultaneous determination of sodium and potassium ions using a voltammetric ion-selective electrode based on the DB 15 C 5-containing nitrobenzene/water interface. Other important features of the two types of the electrochemical analyses are discussed.