Ultrafiltration of protein solutions through partially permeable membranes — the effect of adsorption and solution environment

In the ultrafiltration of proteins through partially-permeable membranes both flux and rejection are time-dependent. Flux shows an initially rapid and then a more gradual decline which is attributable to loss of porosity by internal adsorption followed by surface adsorption. Rejection rises steadily as adsorption reduces the effective sieving coefficient of the membrane. The influence of pH and ions on long-term flux is explained by conformational changes and charge effects in the solute deposited on the membrane. Subtle differences in rejection as a function of solution environment can also be explained by these effects.