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

Macroporous chitosan membranes with controlled pore sizes and good mechanical properties were prepared and cross-linked 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 (∼99%) obtained in a single pass. These membranes showed high stability and reproducibility.