On the Measurement of Solute Partial Molar Volumes in Near-Critical Fluids with Supercritical Fluid Chromatography

Abstract

The use of supercritical fluid chromatography measurements to obtain solute partial molar volumes at infinite dilution is investigated by a combination of theory, modeling, and thermodynamic connections to solubility. Though it is common to ignore contributions from solute self-interactions, theory and modeling show that these can be significant in the critical region. In particular, expressions for the first-order solute composition dependence in terms of convergent infinite-dilution quantities are used to estimate the errors introduced by ignoring solute self-interactions. These are considered in light of recent empirical work on solubilities and partial molar volumes that can be connected via thermodynamic relations. Finally, though various assumptions have been made about the solute partial molar volume in the stationary phase, none of these seem consist with solubility measurements which suggest that the stationary phase contribution should be both temperature- and density (pressure)-dependent.