Comparative Studies of Hydrodynamics and Mass Transfer on Perfusion and Monolithic Chromatography Media

Both the monolithic and perfusive chromatographic media have bimodal pore size distribution, which contributes to higher column throughput and higher column efficiencies compared to the conventional particulate stationary phases. A systematic comparative study on these two types of column media was performed to elucidate the similarities and differences of them and also to further understand the hydrodynamics and mass transfer behaviors of these media. Two kinds of reversed-phase perfusive media (POROS R1/H and POROS R2/H) and two monolithic columns (a polymer-based monolithic RP-pro and a silica based monolithic column RP-18e) were used for comparison. Both monolithic columns have larger throughpores and smaller diffusive pores compared to the perfusive columns. A significant difference in pore size distribution and pore geometry was revealed among these four media; Monolithic RP-18e had the most homogeneous while Monolithic RP-pro the most heterogeneous pore size distributions. The effects of pore sizes, geometry, porosity, solute molecular sizes and flow velocity on axial dispersion and column efficiency were examined. Model simulations using the Knox equation, the van Deemter equation and a power-law relationship were applied to elucidate the different velocity dependence of the axial dispersion of the columns; the Van Deemter equation was found to be sufficient to analyze band dispersion of the silica-based monolithic stationary phase only. Compared to the perfusive columns, the larger throughpore sizes of the monolithic columns mainly accounted for the decreased contribution of the axial dispersion to band spreading and thus increased column efficiency. In addition, the homogeneity of the pore size distribution and the solute molecular size also played very important roles in axial dispersion. Finally breakthrough study was carried out to further characterize the mass transfer behaviors of the monolithic columns and compared to one of the perfusive columns.

Keywords: Monolithic columns; perfusion columns; axial dispersion, hydrodynamics; mass transfer