MEMBRANE-POTENTIALS IN CHARGED MEMBRANES SEPARATING SOLUTIONS OF WEAKELECTROLYTES

The transport of weak electrolyte ions through a charged membrane has been studied. The membrane potential across cation- and anion-exchange membranes was measured for acetic acid and glycine methyl ester hydro chloride aqueous solutions. Membrane potentials were correlated to a t ransport theory using the Donnan equilibrium and the Nernst-Planck equ ation of ion flux by introducing the dissociation constant of a weak e lectrolyte in aqueous solution. The anion-to-cation mobility ratios in the membrane were determined via a non-linear regression method. In t he case of acetic acid solutions in an anion-exchange membrane, the ra tios were about 0.0001-0.001 times larger than those in water. On the other hand, they were about 10000 times larger than in water if a cati on-exchange membrane was employed. Therefore, the ion mobilities of we ak electrolytes are significantly affected by groups of fixed charge i n the membrane. In the case of glycine methyl ester hydrochloride, the mobility ratio was the same as in water, which means that it behaves as a strong electrolyte. It is suggested that the transport phenomena of weak electrolyte ions in a charged membrane can be explained by the above-described transport theory.