Relative Retention in Supercritical Fluid Chromatography as a Source of Partial Molar Properties

Abstract

In addition to its significance as an analytical tool, supercritical fluid chromatography also provides a useful technique for measurement of thermodynamic properties. The purpose of this contribution is to point out some advantages of using the relative retention of a pair of solutes to obtain the solute partial molar properties in supercritical solvents. First, the particular benefits of using the relative retention are shown at the general thermodynamic level of the problem. Next, the Flory−Huggins equation of state (EOS) is employed to derive the correction terms for the composition derivatives of the solute chemical potentials that can readily be used in reducing the experimental retention data to the partial molar properties. When the Flory−Huggins EOS is combined with the regular solution theory, the corrections require pure-component parameters only. Further, as thermodynamic data on isomeric solutes are often of interest in applications of supercritical solvents, the additional simplifications in the correction terms for isomeric solutes are explicitly included.