Cross-linked macroporous chitosan anion-exchange membranes for protein separations

Macroporous chitosan membranes with controlled pore sizes and good mechanical properties were prepared and crosslinked with ethylene glycol diglycidyl ether to increase their chemical stability. Because of their amine groups, they can serve as anion-exchangers (with an ion-exchange capacity as high as 0.83 meq/g dry cross-linked membrane) and can be employed for protein separations in the ion-exchange mode. At pH<7, their surface is positively charged. and they can adsorb proteins with a pI<6 at appropriate pHs. Five proteins, namely ovalbumin (pI=4.6), human serum albumin (pI=4.8), soybean trypsin inhibitor (pI=4.5), lysozyme (pI=11) and cytochrome C (pI=10.6) were selected as model proteins to investigate their adsorption on the chitosan membranes. Relatively high dynamic capacities were achieved at a flow rate of 2 ml/min, namely 11.6, 19 and 20.8 mg/ml membrane for human serum albumin, ovalbumin and soybean trypsin inhibitor, respectively. These proteins could be efficiently recovered (91-98%) from the membranes using a 1 N NaCl in 0.02 N sodium phosphate solution (pH 6) as eluant. Protein separations were performed from binary mixtures (ovalbumin-lysozyme, human serum albumin-cytochrome C, and soybean trypsin inhibitor-cytochrome C), and high purity products (similar to 99%) obtained in a single pass. These membranes showed high stability and reproducibility. (C) 1998 Elsevier Science B.V. All rights reserved.