Protein adsorption and desorption on gel-filled rigid particles for ion exchange

Adsorption and desorption rates of lysozyme onto gel-filled rigid particles for ion-exchange chromatography are measured. The adsorbent medium, known as S-HyperD, comprises polystyrene-coated silica particles whose pores are filled with a functionalized poly(acrylamide)-based hydrogel. The equilibrium uptake decreases gradually with salt concentration in the range 0-150 mM, and no uptake occurs at concentrations of 300 mM or greater. In the low salt range, the rates are consistent with a homogeneous diffusion model where the driving force is the bound protein concentration gradient. As a result of highly favorable partitioning in the gel, transport rates are higher than predicted for diffusion in liquid-filled pores. At high salt concentrations, the measured rates are still consistent with the model, but the diffusivity is higher. In all cases, intraparticle transport is independent of hydrodynamics. The behavior of cyclic column operations is successfully predicted using this model.