SURFACE MODIFICATION OF MICROPOROUS POLYAMIDE MEMBRANES WITH HYDROXYETHYL CELLULOSE AND THEIR APPLICATION AS AFFINITY MEMBRANES

Activated membranes for covalent immobilization of hydroxyethyl cellulose (HEC) were obtained by reaction of microfiltration nylon membranes (N66) with bisoxirane or formaldehyde. Covalent linkage of HEC was essential for the reduction of non-specific interactions with proteins and yielded a HEC coating as a layer of extended coils at the porous network of the membrane after both activation methods, thus reducing the water permeability of the modified membranes. Immobilization of iminodiacetic acid (IDA) onto HEC-coated membranes via standard oxirane chemistry provided IDA affinity membranes with almost identical properties to IDA chromatographic sorbents. The extended coil structure of the coating accounts for protein capacities higher than a theoretical monolayer coverage would yield. The thermodynamics of the interaction of metal chelate affinity (MCA) membranes with the proteins lysozyme, ovalbumin (OVA) and concanavalin A (Con A) demonstrated that dissociation constants K-D>10(-5) M are unsuitable for the retention of target proteins on a single membrane disc. This was demonstrated by the separation of a protein mixture of lysozyme (K-D approximate to 10(-5) M) and Con A (K-D approximate to 10(-7) M) on an MCA membrane.