Isotherm Type Shift of Hydrophobic Interaction Adsorption and its Effect on Chromatographic Behavior

Adsorption isotherm type is a key factor in simulating chromatographic profiles. In this study, the adsorption isotherm type of pure bovine serum albumin (BSA) and immunoglobulin G (IgG) on hydrophobic interaction chromatography (HIC) media was found to shift from Freundlich to Langmuir with the increase of salt concentration. For BSA on butyl-, phenyl- and octyl-sepharose, the isotherm type shift occurred when the salt concentrations were higher than 1.8, 1.5 and 1.4 mol/L, respectively. For IgG, the turning points were 1.0 mol/L on phenyl-sepharose and 0.9 mol/L on octyl-sepharose. Circular dichroism spectra and high-performance size-exclusion chromatography found no obvious conformational change or oligomer formation for the proteins in the solutions with different salt concentrations. HIC profiles of BSA and IgG revealed that the isotherm type shift greatly affected the chromatographic behavior, because the original single peak was coincidentally split into two peaks at the salt concentrations over which the isotherm type shift occurred. Combining both the isotherm type shift and peak-splitting phenomena, it was possible that the change of protein protein repulsion among adsorbed protein molecules under different salt concentrations caused the abnormal behavior of adsorption isotherm and chromatographic profiles.