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The effect of in-place regeneration of protein A adsorbents on protein adsorption characteristics is investigated. Regeneration with sodium hydroxide and time of exposure determined the protein capacity of the adsorbent, but no effect was observed on the adsorbent protein affinity. Fixed-bed adsorption of human immunoglobulin G was studied. Breakthrough curves were measured for protein adsorption on fixed-bed columns. These data were analyzed by a simple kinetic model to determine the rate constants for the adsorption process. It was found that forward adsorption rate constant remained constant along the chemical treatment exposure time. Protein A adsorbent selectivity was determined using mouse serum immunoglobulins G 1 and G 3 . Column linear gradient elution showed that adsorbent selectivity decreased with the exposure time chemical treatment. The implications of these results on the design and optimization of protein A chromatographic process are discussed. List of symbolsA cross-sectional column area c solute concentration in the bulk phase, mg/ml c o solute concentration in the bulk phase at column inlet, mg/ ml c 3 solute concentration in the bulk phase at equilibrium, mg/ml D ligand adsorption site F volumetric flow-rate through packed bed, ml/min k 1 lumped forward adsorption rate constant, ml/mg-min k ÿ 1 lumped reverse adsorption rate constant, 1/min K d dissociation constant, mg/ml L length of fixed bed, cm n dimensionless number of transfer units for overall process P molecule of protein P:D complex between protein and ligand-adsorbent q average adsorbate concentration, mg/ml adsorbent q 3 adsorbate concentration at equilibrium, mg/ml q m maximum binding capacity of adsorbent, mg/ml q s m maximum binding capacity of adsorbent, mg/ml adsorbent settled volume r dimensionless separation factor t time, min T chemical treatment exposure time, h V volume of the fixed bed, ml z axial distance along the fixed bed, cmGreek letters t; L dimensionless solute concentration void fraction of the fixed bed dimensionless effluent volume superficial velocity, cm/min

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