| Abstract
| - Supported liquid membranes are used here to establishsteady-state concentration profiles across ion-selectivemembranes rapidly and reproducibly. This opens up newavenues in the area of nonequilibrium potentiometry,where reproducible accumulation and depletion processes at ion-selective membranes may be used to gainvaluable analytical information about the sample. Untiltoday, drifting signals originating from a slowly developingconcentration profile across the ion-selective membranemade such approaches impractical in zero current potentiometry. Here, calcium- and silver-selective membranes were placed between two identical aqueous electrolyte solutions, and the open circuit potential wasmonitored upon changing the composition of one solution.Steady state was reached in ∼1 min with 25-μm porouspolypropylene membranes filled with bis(2-ethylhexyl)sebacate doped with ionophore and lipophilic ion exchanger. Ion transport across the membrane resulted onthe basis of nonsymmetric ion-exchange processes at bothmembrane sides. The steady-state potential was calculatedas the sum of the two membrane phase boundary potentials, and good correspondence to experiment was observed. Concentration polarizations in the contactingaqueous phases were confirmed with stirring experiments. It was found that interferences (barium in the caseof calcium electrodes and potassium with silver electrodes) induce a larger potential change than expectedwith the Nicolsky equation because they influence thelevel of polarization of the primary ion (calcium or silver)that remains potential determining.
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