Infinite-Dilution Partial Molar Properties of Azulene and Acenaphthylene in Supercritical Carbon Dioxide

Abstract

The effects of temperature and pressure on retention of azulene and acenaphthylene in supercritical fluid chromatography are investigated within 33−58 °C and 74−150 bar. The retention factors are used to derive the infinite-dilution partial molar volumes of the two solutes in supercritical carbon dioxide and infinite-dilution molar enthalpies of the transfer of azulene from the stationary phase to supercritical CO2. The partial molar volumes are converted to quantities characterizing short-range interactions between CO2 and the aromatic hydrocarbon. The results obtained by analyzing the retention data in the usual way are compared with a more refined treatment that takes account of the pressure- and temperature-dependent dissolution of CO2 in the stationary polymer (poly(dimethylsiloxane)) within the column. The corrections for composition changes in the stationary phase employ a combination of the Flory−Huggins theory, the regular solution theory, and the Panayiotou−Vera lattice-fluid model. Application of the composition correction makes the partial molar volumes and the transfer enthalpies more negative. It has recently been noted [Liu, H.; O'Connell, J. P. Ind. Eng. Chem. Res. 1998, 37, 3323] that the chromatographic values of partial molar volumes appear to be systematically less negative than those derived from solubility data. Therefore, the composition correction may help to reconcile the disparity between the chromatographic and the solubility values of partial molar volumes.