(640d) Hindered Diffusion of Biomolecules in Porous Chromatographic Beads

Biomolecular diffusion inside porous chromatographic beads is influenced by the shrinkage of the effective cross-sectional area of the pores. This is because biomolecules are often comparable in size to the pore diameters, and the adsorbed molecules occupy a finite volume, which can partially or completely obstruct the pores. A model, taking into account this phenomenon, is being developed for improved understanding of the role played by intra-particle diffusion in chromatographic separation. The model considers the pores as independent, dead-end cylinders, whose diameters can be determined from the experimentally evaluated pore size distribution of the column. The pore diameter and the diffusion coefficients are considered varying along the pore length and are the functions of the quantity of molecules adsorbed. Two kinds of diffusive behaviour have been considered, (1) pore diffusion, which is the diffusion of the non-adsorbed components through the stagnant mobile phase and (2) surface diffusion, which is the diffusion of the adsorbed components. Values of the respective diffusion coefficients are estimated based on the data from a set of experimental studies developed for this purpose. The diffusion aspect is further analysed in the case of multicomponent systems with competitive adsorption/ desorption processes occurring inside the pores, and their effect on the overall separation behaviour in the column. The presentation will describe the salient features of the model, and discuss the results in light of these features.