A validated model for the simulation of protein purification through affinity membrane chromatography

A mathematical model is proposed for the description of protein purification through membrane affinity chromatography. The model describes all the three stages of the chromatographic cycle and takes into account convection, axial dispersion and binding reaction kinetics in the porous membrane matrix, while boundary layer mass transfer resistance is shown to be negligible. All the model parameters have a precise physical meaning which enables their evaluation through separate experimental measurements, independent of the chromatographic cycle. Model testing and validation has been performed with experimental chromatographic cycles carried out with pure IgG solutions as well as with complex mixtures containing IgG1, using new affinity membranes. The comparison between model calculations and experimental data showed good agreement for all stages of the affinity cycle. In particular, for loading and washing steps binding kinetics was found so fast that adsorption equilibrium was sufficient to describe the observed behavior; as a result, the model simulations are entirely predictive for the adsorption and washing phases. On the contrary, in the elution step the reaction rate is comparable to that of the other simultaneous transport phenomena. The model is able to predict the performance of chromatographic purification of IgG from complex mixtures simply on the basis of the parameter values obtained from pure IgG solutions.