The characterisation of the surface charge of a cobalt spinet ultratiltration membrane was investigated in the presence of electrolyte solutions by means of streaming potential measurements. The selectivity of a membrane towards different salts depends on the electrostatic interactions between the species in solution and the charge of the membrane surface. Firstly, the values of the streaming potential coefficient were measured during the filtration of NaCl, CaCl2. Na2SO4 and CaSO4 as a function of pH and ionic strength. The iso-electric point was determined for each electrolyte. Secondly, the rejection rates of the electrolytes were measured by ionic chromatography. The rejection was explained by a correlation with the surface charge of the membrane. (c) 2005 Elsevier B.V. All rights reserved.