Mass transfer mechanisms in Hyper D media for chromatographic protein separation

In order to elucidate the mass transfer mechanisms that allow improved perf ormance for the separation of proteins of the chromatographic packing mater ial Q Hyper D (BioSepra, Villeneuve la Garenne, France), when compared with traditional packing materials, several experiments were carried out using a commercial HPLC column, with BSA and myoglobin as test proteins. First, e lution chromatographic runs under unretained conditions at several flowrate s and protein concentrations were made. The HETP vs. superficial velocity p lot is almost a plateau, except for the low flowrate region. Elution experi ments were also carried out under weakly retained conditions (with salt con centration 0.3 M NaCl) in the linear region of the adsorption equilibrium i sotherm. Using Rodrigues' equation, the experimental initial slope and plat eau of a Van Deemter plot enable the determination of the effective diffusi vity and particle permeability respectively. Then, breakthrough experiments under retaining conditions were run at several feed concentrations and flo wrates. The experimental adsorption equilibrium isotherm is rectangular; us ing a simplified fixed-bed adsorber model for rectangular isotherms, an app arent (augmented) diffusivity is calculated as a function of flowrate. The determined augmented diffusivities are shown to follow the dependence on ve locity established by Rodrigues et al.; this clearly shows that intrapartic le convection is present as a mass transfer mechanism, since the real intra particle diffusivity is independent of flowrate. (C) 1998 Elsevier Science S.A.