Separation of proteins by surface modified polysulfone membranes

Ultrafiltration separation experiments on mixed solution of bovine serum albumin and γ-globulin were performed in a stirred batch cell through unmodified and surface modified polysulfone membranes, γ-Globulin permeated through the surface modified membrane to some extent but the bovine serum albumin was 100% rejected towards the end of the concentration process at pH 7.2 and 9.0, although the molecular weight of γ-globulin is higher than that of bovine serum albumin. The unmodified membrane did not extensively separate the proteins in the mixed solution at any pH, unlike the surface modified membrane. It is suggested that the separation between bovine serum albumin and γ-globulin through the surface modified membranes is caused, not by a sieving effect or by charge repulsion between membranes and proteins, but by the balance of hydrophilic and hydrophobic segments on the surface of the modified membranes.