Competitive sorption of low and high molecular weight proteins in model mixtures by Q HyperZ chromatographic medium. Part II: Mass transfer mechanisms

Abstract

The kinetic uptake of Bovine Serum Albumin (BSA) and ferritin in mixtures by the composite anion exchanger Q HyperZ was studied. Transient adsorption experiments were performed to investigate the dominant resistance between external and internal mass transfer in simultaneous and sequential adsorption experiments. From the evolution of protein solution concentration with time, the external mass transfer coefficients determined were very low in simultaneous (7.1 10−7 and 1.1 10−7 m/s for BSA and ferritin respectively) and sequential (4.6 10−7 and 2.5 10−7 m/s for BSA and ferritin respectively) adsorption systems which is in agreement with the low agitation speed used. From the transient protein uptakes, the internal mass transfer was studied and the homogenous diffusion model applied provides a good predictability in single as well as in simultaneous and sequential adsorption experiments. The effective diffusion coefficients were determined in sequential (6.4 10−14 m2/s and 3.8 10−14 m2/s for BSA and ferritin respectively) and simultaneous (4.2 10−14 m2/s for both proteins) systems. In multi-component adsorption system, it was found that BSA was slowed down upon the presence of ferritin on mixture solutions contrarily to ferritin protein. This phenomenon, known as electrostatic coupling effect, indicates that diffusion of charged proteins in ion exchangers are not independent.