Electrostatic interactions between immunoglobulin (IgG) molecules and a charged sorbent

The influence of electrostatic interactions on the adsorption of IgG is examined both theoretically and experimentally. The long-range interaction between IgG and the charged sorbent surface is treated in terms of the DLVO theory taking into account the possibility of charge- and potential regulation upon approach of IgG towards the surface. The relevant electrostatic and van der Waals interactions are a combination of interactions between IgG molecules and the sorbent surface (hetero-interaction part) and interactions between adsorbed and incoming IgG molecules (homo-interaction part). Experiments are performed on hydrophilic surfaces, namely negatively charged silica and positively charged amine-functionalised silica. It is concluded that electrostatic interactions have a strong influence on the adsorption behaviour. Excellent agreement was found between experiment and theory with respect to the dependence of the adsorption kinetics on pH and ionic strength. Furthermore, the steady-state adsorbed amount as a function of these variables is satisfactorily accounted for.