Relative rates of protein transmission through poly(acrylonitrile) based ultrafiltration membranes

Abstract

The ultrafiltration of bovine serum albumin (BSA) and hemoglobin (Hb) was carried out with membranes prepared from acrylonitrile homopolymer (PAN) and its copolymer with acrylamide (PAN-A). Both proteins have similar molecular weights; however, BSA has an isoelectric point at pH 4.8 while Hb is positively charged upto pH 6.8 and is also more hydrophobic. Measurements were made with both single and mixed protein solutions over a pH range 4.0–7.5. The flux and rejection data can be explained by protein adsorption and consequent pore narrowing, as a result of hydrophobic and electrostatic interactions. In the case of the more hydrophilic PAN-A membrane, electrostatic interactions between protein and the negatively charged membrane lead to decreased protein adsorption/pore narrowing and a corresponding increase in flux and decrease in protein rejection as pH is increased above the IEP. For Hb ultrafiltration through the PAN membrane where hydrophobic interactions would be strongest, the rejection is relatively constant and the flux exhibits a minimum at the IEP. The protein rejection trends observed during single protein UF are very different when both BSA and Hb are ultrafiltered together. The binary solution rejection trends can be explained by preferential adsorption of Hb and by BSA-Hb electrostatic interactions.