Infinite-dilution partial molar properties of naphthalene and biphenyl in carbon dioxide from supercritical fluid chromatography: Composition effects in the stationary phase

초록

The temperature and pressure effects on retention of naphthalene and biphenyl in supercritical fluid chromatography are investigated within 35-70 °C and 75-150 bar. The retention factors are used to derive the infinite-dilution partial molar volumes of the two solutes in supercritical carbon dioxide, and the infinite-dilution molar enthalpies of transfer of the two solutes from the stationary phase to supercritical CO<inf>2</inf>. The partial molar volumes are converted to quantifies characterizing short-range interactions between CO<inf>2</inf> and the aromatic hydrocarbon. The resultant partial molar properties are corrected for the pressure- and temperature-dependent dissolution of CO<inf>2</inf> in the stationary polymer (poly(dimethylsiloxane)). The corrections for composition changes in the stationary phase include a composition derivative of the solute chemical potential that can only be obtained from a suitable theoretical model. Therefore, it is difficult to give a conclusive account of the performance of the corrections as these reflect the features of the model employed; here, the Scatchard-Hildebrand-Flory-Huggins theory or the Panayiotou-Vera lattice-fluid model are used for the purpose. However, comparison of the resultant partial molar volumes of naphthalene with literature data from high-precision, vibrating-tube densitometry indicates that the composition corrections improve the agreement between chromatographic and densitometric results.