Bi-ionic potentials across liquid cation exchanger membranes

Abstract

Using cation exchanging solutions of dipicrylaminate, DPA, as membranes of extreme cationic selectivity, bi-ionic potentials, B.I.P.s, are studied in cells of the type: A +M − c 1 liquid DPA salts in o-nitrotoluene {B +M − c}. The factors that have to be considered in constructing an experimental system that approaches the ideal requirements of such a cell are discussed. The B.I.P.s are found to be essentially independent of ion exchanger concentration in the membrane and essentially independent of the concentration of the aqueous solutions as predicted by theory. The magnitudes of the B.I.P.s depend upon the separation of the cations in the Hofmeister series, and are additive in the sense: B.I.P. A +/B + + B.I.P. B +/C + = B.I.P. A +/C + . The sodium-potassium cell measured 108 mv (sodium side positive) while the highest potential of 225 mv was found with the lithium-cesium cell (lithium side positive).