Modeling electrostatic exclusion effects during ion exchange chromatography of monoclonal antibodies

Recent experimental studies have shown a reduction in dynamic- binding capacity for both monoclonal antibodies and antigen-binding fragments at very low conductivity, conditions that should generate the greatest electrostatic attraction. This behavior has been attributed to the steric and electrostatic exclusion of the charged protein from the entrance of the resin pores. This manuscript presents a quantitative mathematical description of this phenomenon. The protein partition coefficient was evaluated using models for the partitioning of a charged sphere into a charged cylindrical pore, with the pore size distribution evaluated by inverse size exclusion chromatography. The results were in very good agreement with experimental data for batch protein uptake and dynamic-binding capacity over a range of pH and conductivity. This theoretical framework provides important insights into the behavior of ion exchange chromatography for protein purification.