Membrane potential is a measurable and reliable parameter to characterize the charge property of membrane. Membrane potentials have been measured across polystyrene based titanium arsenate membrane separating various 1:1 electrolytes at different concentrations. Membrane potential data have been used to calculate transference number of ions, mobility, distribution coefficient, charge effectiveness, permselectivity and also to derive the thermodynamically fixed charge density which is an important characteristic governing the membrane phenomena by utilizing the generally accepted theories for the salt concentration dependence of uni-univalent potentials, proposed by Teorell-Meyer-Sievers and Kobatake method and these are compared in order to obtain a relationship for the theoretical data of uni-univalent potentials. The good agreement between the theoretical and the experimental data of uni-univalent potentials proves the applicability of the relationship derived to the membrane system. Kobatake's equation was used under two limiting conditions, namely in the concentration range and in the dilute range. The two limiting forms of Kobatake's equation gave identical values of theta for the membrane taken in this investigation. Membrane is negatively charged (cation selective) and the selectivity increases with dilution. The structure of the membrane was observed with the aid of a scanning electron microscope. The order of fixed charge density for electrolytes used is found to be KCl > NaCl > LiCl. (C) 2009 Elsevier Ltd. All rights reserved.