Experimental studies on bi-ionic potentials across permselective membranes

Abstract

1. 1. The theoretical and experimental limitations are discussed of the measurement of the dynamic bi-ionic membrane potential, B.I.P., which arises across a membrane separating the solutions of two electrolytes at the same concentration having different “critical” ions which are able to exchange across the membrane and the same “noncritical” ion species for which the membrane is impermeable. Particular attention is given to the influence of the “diffusion layers” adjacent to each surface of the membrane. 2. 2. The B.I.P.'s with a variety of pairs of critical ions across several types of cation-selective and anion-selective permselective collodion-matrix membranes show that the electromotive efficacy of the various cations and anions corresponds to their position in the Hofmeister series. The absolute magnitude of the bi-ionic potentials depends on minor differences in the mode of preparation of the permselective membranes. 3. 3. The B.I.P. with a given pair of critical ions across a given membrane is independent of the nature of the noncritical ions. 4. 4. The B.I.P. with a given pair of critical ions is nearly constant within the range of concentration in which the diffusion layers do not play a disturbing role. 5. 5. Some problems of membrane specificity and their biological implications are briefly discussed.