A new modified Hittorf method for the determination of transport numbers in polyelectrolyte solutions

Abstract

A new method for determining transport numbers in polyelectrolyte solutions is described. The method is a modification of the Hittorf method, the main difference being that the current-induced concentration change is measured in a compartment to which current is supplied through an ion-exchange membrane. As the current in the membrane is carried by counterions only, the solution in the measuring compartment remains free from foreign ions, and thus the concentration change can be monitored accurately by conductivity measurements. Experiments have been carried out with sodium and potassium salts of polyacrylic acid and carboxymethylated hydroxyethyl cellulose of low degree of substitution. The measurements clearly indicate that for polyacrylic acid a difference exists in the ion binding of Na⁺ and K⁺ ions and that the polyion equivalent conductivity is dependent on the counterion species.