POLAR AND NONPOLAR COSOLVENT EFFECTS ON THE SOLUBILITY OF CHOLESTEROL IN SUPERCRITICAL FLUIDS

The solubility of cholesterol in supercritical carbon dioxide and ethane containing small amounts (1.76-6.0 mol %) of acetone and hexane cosolvents has been measured. The data show an unusual reversal of cosolvent effects in the different primary supercritical fluids. These results are interpreted in terms of the competition between dispersion and dipole interactions and the molecular features of cholesterol. The highest solubility is observed in the ethane-acetone system where ethane interacts with the hydrocarbon backbone of cholesterol and acetone interacts with the polar OH group. The results are correlated with a modified form of the Peng-Robinson equation of state. The necessity of characterizing solute properties for supercritical fluid extraction of biomolecules is highlighted.