Effect of Density on Enthalpy and Entropy of Transfer for Supercritical Fluid Chromatography

摘要

The effect of density on the enthalpy of transfer and the entropy of transfer of the solute between the mobile and stationary phase was investigated for capillary supercritical fluid chromatography (SFC) using carbon dioxide as the mobile phase. The solutes were n-alkanes and n-alkanols and the stationary phases were coated in-situ cross-linked SE-54 and OV-17. Enthalpies were seen to decrease as fluid density increased over a range of 0.20 to 0.50 g/cc. The range of enthalpies were from -5.9 to -8.4 kcal/mol for OV-17 and -3.9 to -8.6 kcal/mol with SE-54. The entropy ranged from -7.1 to -16.2 cal/mol.K for SE-54 and -12.5 to -17.0 cal/mol.K for OV-17. The results demonstrate the interdependence of enthalpy and entropy of transfer with supercritical fluid density during chromatographic separations.