CONCENTRATION POLARIZATION AND ADSORPTION EFFECTS IN CROSS-FLOW ULTRAFILTRATION OF PROTEINS

Reported here are the first results of a study which attempts to experimentally quantify the relationships between the localities of protein adsorption and permeate flux in the ultrafiltration of protein solutions. Radioactively labelled serum albumin has been used to investigate the adsorption and polarisation in the cross-flow ultrafiltration of protein solutions. In-situ measurements of both phenomena were made using a scintillation detector mounted directly above the filtration flow channel. This in-situ method allowed direct measurement of the amounts of retained protein, either held dynamically or both weakly and strongly adsorbed to the membrane. The adsorption behaviour of the polymer alone was found using powders prepared by phase inversion. Significant differences in the polarisation and adsorption were observable for filtrations at differing pHs. The major amount of protein is held dynamically, by a factor up to 9 times that of the membrane surface adsorption. This amount is pH dependent. There are significant differences between weakly and strongly held protein near the iso-electric point. There is little difference between these at pHs far from the iso-electric point. The strong adsorption behaviour of the membrane is similar to the observed behaviour of the polymer. Results at the iso-electric point here are unclear, due probably to the complicating effect of molecular aggregation. A conclusion that can be drawn from this work is that it is a combined polarisation-adsorption which appears to control the permeation rate. For a case of similar fluxes distinct differences exist between observed adsorption and polarisation.