Model for retention and efficiency in open-tubular supercritical fluid chromatography

Abstract

A model for open-tubular supercritical fluid chromatography at constant mass flow-rate, which takes into account the effects of temperature, density and pressure drop on solute retention and dispersion, is developed and applied to the elution of normal alkanes (C 8-C 40) on a polysiloxane stationary phase using CO 2 mobile phase using CO 2 mobile phase at 40 to 120°C. An exact expression for resolution is derived in terms of observed chromatographic parameters, and the effect of swelling on solute diffusion coefficients in the stationary phase is considered. Plots of apparent plate height vs. temporal average velocity show the onset of gradient-induced band spreading for a variety of conditions. Swelling of the stationary phase is shown to be critical to the achievement of acceptable efficiency for heavy solutes at low temperatures, and the prediction of a second maximum in resolution at high mobile phase velocities suggests the possibility of extremely fast separations by supercritical fluid chromatography.