The effect of ph and ionic environment on the ultrafiltration of protein solutions with retentive membranes

Abstract This paper discusses the ultrafiltration (UF) of protein (BSA) solutions with retentive membranes over a range of pH values (2—10) and salt concentrations. UF flux transients, following a step input of salt, produced flux drops at pH 2 and 10, but flux increase at pH 5. For long-term runs with fixed feed the flux declined at all pHs and salt contents. Initial and long-term fluxes varied with pH. A flux minimum occurred at pH 5 in the absence of salts, but in the presence of 0.2 M NaCl the monotonically with pH. The final UF flux was found to correlate with the amount of adsorbed protein, particularly in the absence of salts. Maximum adsorption occurred at the isoionic/isoelectric points (≊pH 5), and it was greater in the presence of salts. The results are explained in terms of the effect of different ionic environments on the permeability of the deposited protein. Conformational changes and charge properties of the BSA appear to be the dominant factors determining the flux.