ADSORPTION CHARACTERISTICS OF AN IMMOBILIZED METAL AFFINITY MEMBRANE

An immobilized metal affinity (IMA) hollow-fiber membrane was prepared by radiation-induced graft polymerization of glycidy methacrylate (GMA) onto a porous polyethylene hollow fiber, followed by chemical conversion of the produced epoxide group into an iminodiacetate (IDA) group and its chelation with copper(II) ion. The IDA hollow fiber, whose degree of GMA grafting was 120%, was found to retain 0.42 mol of Cu ion/kg of dry weight of the resulting IMA hollow fiber. The pure water flux of the affinity membrane was 0.90 m/h at a filtration pressure of 1 x 10(5) Pa. The 0.1 g/L L-histidyl-L-leucine (His-Leu) solution permeated across the IMA hollow fiber, whose inner diameter and thickness were 0.78 and 0.365 mm, respectively, at a prescribed filtration pressure ranging from 0.2 x 10(5) to 1.0 x 10(5) Pa. The adsorption of His-Leu during permeation of the solution showed that the overall adsorption rate was independent of the filtration pressure, i.e., the residence time, because of the negligible diffusional resistance of His-Leu to the pseudobioaffinity ligand located on the pore surface of the membrane. No deterioration in the adsorption capacity was observed after five cycles of His-Leu adsorption, its elution, and reimmobilization of copper. The adsorption isotherm of bovine serum albumin (BSA) on the IMA hollow fiber was measured and compared with that for the conventional agarose-based bead containing the IDA-Cu ligand. The diol group formed by H2SO4 treatment of the epoxide group remaining after conversion of epoxide into IDA functionality significantly reduced the nonselective adsorptivity of His-Leu and BSA on the membrane.