Dissociation events during processing of monoclonal antibodies on strong cation exchange resins

The phenomenon of pH excursion was demonstrated for pH gradient elution of monoclonal antibodies (mAbs) on strong cation exchange resins under high overloading conditions. The mAbs differed in molecular structure and isoelectric point, and the resins in matrix structure and ligand density. In all cases, elution of the proteins was accompanied with distortion of the concentration, pH and conductometric profiles. To elucidate that phenomenon, titration curves were generated for liquid solutions of the proteins as well as for suspensions of the resins with the proteins adsorbed on their surface. The course of the curves was found to be affected by the presence of the proteins both in liquid and adsorbed phases. The effect enhanced with increase in the initial pH of the binding buffer and in the protein concentration. To quantify that phenomenon, a mechanistic model was used, which accounted for the protein dissociation in both phases. The model reproduced the titration curves and the observed trends in changes of their courses. The simulation results indicated that the pattern of pH transitions recorded for different mAbs on the resins mostly depended on their adsorption affinity.