ABSTRACT
Solid ion-selective electrodes are based on materials which can be broadly classified as ion exchangers. Suitable materials are insoluble in ionogenic solvents, athough they adsorb and may absorb solvents. The classification "ion exchanger" includes materials which exchange ions of the same kind as their constituents. For construction of practical devices, the ion-exchange process must be rapid and reversible for one ion or the other. Rapidity is measured by the exchange current density or flux, which must be large compared with the current passed by the measuring device. However, this requirement is scarcely a problem with modem measuring circuits. Rates of ion exchange at the silver-based electrodes appear to be rapid and reversible at high-cation or anion activities. Probably the most important and least well-documented requirement for preparation of stable, reversible-interface, ion-exchanging, solid state membrane materials is control of the impurities.
