Adsorption equilibrium and kinetics of monomer–dimer monoclonal antibody mixtures on a cation exchange resin

•Adsorption of mAb monomer/dimer mixtures on CEX resin visualized by CLSM.•Monomer/dimer selectivity varies with salt concentration.•Displacement of monomer by dimer occurs within the resin beads at higher salt.•Intraparticle adsorption fronts are consistent with dual shrinking core model.•Low salt monomer/dimer adsorption not predicted by current isotherm models.

Adsorption equilibrium and kinetics are determined for a monoclonal antibody (mAb) monomer and dimer species, individually and in mixtures, on a macroporous cation exchange resin both under the dilute limit of salt gradient elution chromatography and at high protein loads and low salt based on batch adsorption equilibrium and confocal laser scanning microscopy (CLSM) experiments. In the dilute limit and weak binding conditions, the dimer/monomer selectivity in 10 mM phosphate at pH 7 varies between 8.7 and 2.3 decreasing with salt concentration in the range of 170–230 mM NaCl. At high protein loads and strong binding conditions (0–60 mM NaCl), the selectivity in the same buffer is near unity with no NaCl added, but increases gradually with salt concentration reaching high values between 2 and 15 with 60 mM added NaCl. For these conditions, the two-component adsorption kinetics is controlled by pore diffusion and is predicted approximately by a dual shrinking core model using parameters based on single component equilibrium and kinetics measurements.