Potassium Selective Microelectrodes with Precipitate in the Tip

Abstract

THE thermodynamic analysis of physico-chemical processes in the living cell requires a knowledge of intracellular ionic activities. This problem has stimulated research into the design of special microelectrodes which are selectively sensitive to the different ions. This has been achieved by using either reversible, glass insulated, metal microelectrodes^1,2, or the so-called membrane electrodes³. The interphase potential of a metallic silver–silver chloride electrode, the most commonly used, is a function of the activity of chloride ions in the solution and its selectivity properties are determined by the presence of the silver chloride precipitate layer. In membrane electrode systems, selectivity depends on the ion exchange properties of the membrane material, and the transmembrane potential is a function of the ion activity ratio across the membrane for a particular ion. For the cations H⁺, K⁺ and Na⁺, glass membrane electrodes³ are usually used while silicone–rubber membranes packed with certain precipitates or ion-exchange substances are used for various anions⁴.