Membrane application in proteomic studies: Preliminary studies on the effect of pH, ionic strength and pressure on protein fractionation

The effects of pH, ionic strength and pressure on membrane-modulated protein fractionation were studied. Model protein, bovine serum albumin (BSA), was subjected to various pH, ionic strengths and pressures. The protein content and salt rejection in the retentate and flux were monitored. The design of the experiment was carried out with the aid of response surface methodology (RSM). A set of 20 designed experiments was carried out, and the data collected were analyzed using central composite experimental design in response surface methodology (RSM) by Design Expert, Version 5.0.7 (StatEase, USA). The response surface plot for fluxes was higher at lower ionic strengths and at high pH due to the shielding of charge and the electrostatic repulsion of protein with a similar charge while higher pressure reduced the flux through concentration polarization and expansion of adsorbed BSA on the membrane surface. Chloride rejection was highest at pH 8 and was independent of the salt concentration where the negative charge of BSA was stronger. It was observed that higher pressure seemed to favor rejection.