An organic-inorganic composite material, i.e. polystyrene cobalt arsenate was chemically synthesized by a sol-gel process. The physico-chemical of the membrane was determined using SEM, TGA and XRD studies. The membrane was found to be crystalline in nature with uniform arrangement of particles and no sign of visible cracks. Ionic potentials were measured across polystyrene cobalt arsenate membranes with 1:1 electrolytes at different concentrations. Observed membrane potentials were positive. The membrane potential offered by the electrolytes was in the order of KCl > NaCl > LiCl. The successful application of TMS and Kobatake theory were used for the estimation of the charge density of membranes. The order of charge density for 1:1 electrolytes solution was found to be KCl > NaCl > LiCl. Kobatake's equation was used under two limiting conditions, namely in the high concentration range and in the dilute concentration range. The two limiting forms of Kobatake's equation gave identical values of charge density for the membrane taken in this investigation. The TMS method was used to investigate the transport number of ions, mobility ratio, distribution coefficient, charge effectiveness, perm selectivity and concentration of fixed charge of the membranes. (C) 2011 Elsevier Ltd. All rights reserved.