Thermodynamic pitfalls in chromatography revisited: Supercritical fluid chromatography

Abstract

Relationships between solute retention in supercritical fluid chromatography and thermodynamic properties of solute transfer from the mobile to the stationary phase are reviewed and illustrated with statistical thermodynamic calculations on a model system. Attention is paid to the effect of sorption of the mobile phase fluid into the stationary phase. The nearly linear plots of ln k′ vs. 1/ T at a constant density of the mobile phase fluid (“Van 't Hoff plots”) are shown to be of little use in themselves for determining the solute transfer properties. Apparent linearity of these plots results from cancellation of thermodynamic anomalies near the critical point of the mobile phase fluid.