INTERMOLECULAR ELECTROSTATIC INTERACTIONS AND THEIR EFFECT ON FLUX AND PROTEIN DEPOSITION DURING PROTEIN FILTRATION

Although membrane filtration is used extensively to process protein so lutions containing a variety of electrolytes, there is currently littl e fundamental understanding of the effect of the solution; environment (and in particular, the solution pH) on the filtrate flux in these sy stems. We have obtained data for the flux and sieving coefficients dur ing the batch (stirred cell) filtration of solutions of bovine serum a lbumin, immunoglobulins, hemoglobin, ribonuclease A, and lysozyme thro ugh 0.16-mu m microfiltration membranes at different pH values. The fl ux declined significantly for all five proteins due to the formation o f a protein deposit on the upper surface of the membrane. The quasi-st eady ultrafiltrate fluxes at the individual protein isoelectric pH's w ere essentially identical, despite the large differences in molecular weight and physicochemical characteristics of these proteins. The flux increased at pH's away from the isoelectric point, with the data well -correlated with the protein surface charge density. These results wer e explained in terms of a simple physical model in which the protein d eposit continues to grow, and thus the flux continues to decline, unti l the drag force on the proteins associated with the filtrate,flow is no longer able to overcome the intermolecular repulsive interactions b etween the proteins in the bulk solution and those in the protein depo sit on the surface of the membrane.