An Affinity Complex Titration Isotherm for Mechanistic Modeling in Protein A Chromatography

A pH-dependent affinity complex titration isotherm is derived based on the stoichiometry of target binding and both target and ligand titration equilibria to facilitate mechanistic modeling for protein A chromatography. The final isotherm can be regarded as a direct modification of the Langmuir isotherm with an apparent capacity and equilibrium constant. The model parameters can be estimated from four elution experiments and the same model parameters can be extrapolated to a wide range of situations with accurate chromatogram predictions. The isotherm is shown to be compatible with different mAbs, resins, residence times, wash and elution buffer pHs, gradient lengths from 0 to 30 column volumes and column dimensions. The separation of a mAb mixture is presented as a case study.