Role of electrophoretic mobility of protein on its retention by an ultrafiltration membrane. Comparison to chromatography mechanisms.

Lysozyme and lactoferrin, two globular proteins, were first studied separately in order to elaborate a strategy for the improvement of their separation by ultrafiltration (UF) with zirconia-based membranes of different charge sign and pore radius. The electrophoretic mobility (mu) at fixed pH and variable ionic strength was used for the characterisation of both proteins and zirconia particles, similar to the active layer of the membrane during the UF run. Specific adsorption of phosphate ions was shown for both proteins resulting in new isoelectric points.