Influence of pH and ionic strength on IgG adsorption to vials

It was the aim of this work to investigate the influence of the formulation parameters pH and ionic strength on the adsorption of IgG to borosilicate glass vials. The charge characteristics of IgG and glass surface were determined by isoelectric focusing and electrokinetic measurements. It could be shown that IgG adsorption highly depends on formulation pH and ionic strength. The amount of IgG adsorbed results from an interplay of attractive and repulsive electrostatic interactions between protein molecules and the glass surface as well as among adsorbed protein molecules. The pH value where the ion uptake in the adsorption boundary was minimal coincided well with the pH of maximum adsorption. At pH 4, the presence of Na(2)SO(4) gave rise to a stronger increase in adsorption than NaCl at equal ionic strength, whereas we observed no differences at e.g. pH 7.2 and 8.6. In summary, it can be stated that IgG adsorption on borosilicate glass is to a large extent mediated by electrostatic interactions. Other driving forces like hydrophobic interactions or surface-induced structural alterations contribute to a much lesser extent.