Diffusion and adsorption of proteins in a model pore in the surface forces apparatus

Investigation of pore diffusion hindrance of monoclonal antibody in hydrophobic interaction chromatography using confocal laser scanning microscopy

In this article, hindrance of intraparticle mass transfer during the adsorption of a monoclonal antibody (mAb) on Butyl Sepharose 4FF was investigated under different conditions. In addition to common fluid phase measurements, confocal laser scanning microscopy (CLSM) was applied to evaluate the respective intraparticle concentration profiles. In order to ensure that the observed intraparticle protein distributions are not disturbed by artefacts of CLSM, microscopic data are carefully analysed considering signal attenuation and competitive adsorption between labelled and native species. Using this setup, lower protein concentration in the inner particle region was observed even after long equilibration times in protein solution. Since the observed phenomenon showed a dependency on the amount of adsorbed protein, we assumed that the intraparticle diffusion was hindered by the adsorbed protein molecules. We propose hypotheses on the diffusion hindrance, and compare the experimental results with model-based simulations of single particles that include novel terms for the description of hindered diffusion.

Comparison of protein adsorption isotherms and uptake rates in preparative cation-exchange materials

Adsorption isotherms and effective diffusivities of lysozyme in a set of six preparative cation-exchange stationary phases were determined from batch uptake data in a stirred vessel. Both a pore diffusion and a homogeneous diffusion model were used in estimating diffusivities, with the isotherms fitted to a non-Langmuirian analytical isotherm equation. The capacities inferred from the isotherms are found to be correlated with the surface area accessible to lysozyme, the effective surface concentrations obtained being in agreement with values measured by different methods in various non-chromatographic systems. The pore diffusivities show systematic trends with protein and salt concentration, and effects of pore size and connectivity are also evident. Some trends in the homogeneous diffusivities are quite different to those in the pore diffusivities, but these differences largely disappear when the homogeneous diffusivities are rescaled to account for adsorption equilibrium behavior. Additional information is required to elucidate further the mechanisms of coupled diffusion and adsorption in stationary phases.