Simultaneous correlation of hydrophobic interactions in HIC and protein solubility in aqueous salt solutions and mixed solvents

Abstract

The chromatographic retention in hydrophobic and reversed phase chromatography and the solubility of proteins display some common features. The chromatographic retention, as well as the solubility, is modulated by the thermodynamic properties of the solute in the fluid phase. The retention measurements at linear conditions provide information of the solution properties of the protein at infinite dilution, and the solubility measurements produce the supplementary information about the solution properties at the saturation limit. This provides a useful approach to simultaneous correlation of the chromatographic retention and the solubility. The experimental data, used for the correlation, comprise retention measurements of lysozyme on different HIC adsorbents using an aqueous ammonium sulphate eluant, an aqueous ammonium sulphate eluant with an admixture of ethanol, as well as published solubility data. The chromatographic retention data and the corresponding solubility data have been correlated using a chemical potential model derived from Kirkwood's theory of solutions of charged macro-ions and zwitterions in electrolyte solutions. The model correlated the chromatographic retention factor and the solubility data within the precision of the measurements. The model was applied in a pH range from 4 to 11. It was demonstrated experimentally, as well as theoretically, that an admixture of ethanol to the aqueous eluant changes the thermodynamic retention factor on various adsorbents identically when compared to the thermodynamic retention factor in an ethanol free eluant.