MODEL FOR ION-EXCHANGE EQUILIBRIA OF MACROMOLECULES IN PREPARATIVE CHROMATOGRAPHY

An adsorption model based on the stoichiometric displacement principle was developed for the non-linear ion-exchange of macromolecules. In t his model, the adsorbed phase is a non-ideal surface solution in equil ibrium with a non-ideal bulk liquid, and non-idealities in both phases are quantified in terms of activity coefficient corrections. The equi librium model accounts for the shape and charge of the adsorbates, lat eral interactions on the surface and the effects of modulating salts. Practical methods were developed for evaluating model coefficients, an d the model was applied to overloaded elution chromatography of bovine serum albumin. It is shown that non-idealities in the liquid phase an d lateral interactions on the surface strongly influence elution profi les.