Kinetics of tracer flows and isotope interaction in an ion exchange membrane

Summary The thermodynamic formulation of isotope interaction (coupling of abundant and tracer isotope flows) has been tested in a highly permselective anion exchange membrane in the absence of significant electroosmosis. A previous study of Cl^– permeation has now been extended to include permeation of I^–, Acetate, and SO₄^2– in different bath concentrations, with the use of both electrical and chemical driving forces. The flux ratios were abnormal according to the usual criteria for simple passive flow, but were closely predicted by the theoretical expression incorporating the influence of isotope interaction. In the absence of coupled flows of other chemical species the extent of isotope interaction can be determined either from the flux ratio or from the measurement of a single unidirectional flux at two settings of the electrochemical potential difference. Direct evidence of negative isotope interaction was presented.