An improved process for separation of proteins using modified chitosan-silica cross-linked charged ultrafilter membranes under coupled driving forces: isoelectric separation of proteins

Functionalized chitosan namely as N-methylene phosphonic chitosan (PC) and quaternized chitosan (QC) silica composite charged ultrafilter membranes were prepared by acid catalyzed sol-gel method in the aqueous media and gelated in methanol for tailoring their pore structure. These membranes were employed for developing a simple membrane process for pH sensitive protein fractionation under coupled driving forces (pressure and electric gradient). Protein transmission (selectivity) and membrane throughput across both membranes were studied using binary mixture of protein under different gradients at pH points: 2.0, 4.8, 10.7, and 13.0. It was concluded that separation from the binary mixture of BSA-LYS, separation LYS at pH 4.8 (pI of BSA) using negatively charged PC-Si membrane or separation BSA at pH 10.7 (pI of LYS) using positively charged QC-Si membrane, was possible with high selectivity. Also in all cases, due to coupling of driving forces, filtrate flux and selectivity were enhanced by several folds. Furthermore, applied electric gradient progressively increased the separation factor values, which was close to 10 for PC-Si and 15 for QC-Si membranes. Relatively high separation value of individual protein from binary mixture and filtrate velocity suggests the practical usefulness of this novel process and biopolymer membranes.