Gallium (Ga) ions as an affinity ligand were immobilized to the polymer chain grafted onto a porous hollow-fiber membrane to specifically capture phospho-compounds. An epoxy-group-containing vinyl monomer, glycidyl methacrylate, was graft-polymerized to an electron-beam-irradiated porous hollow-fiber membrane. The partial conversion of the epoxy group into an iminodiacetate group was effective in increasing the molar conversion in the subsequent introduction of a nitrilotriacetate group capable

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... of forming a complex with Ga ions. The amount of Ga ions immobilized was 0.55 mmol per gram of the membrane. The overall rate of adsorption of phosphotyrosine to the Ga-ion-immobilized porous hollow-fiber membrane increased with an increase in the rate of permeation of phosphotyrosine solution through the pores because of the negligible diffusional mass-transfer resistance of phosphotyrosine to the affinity ligand.