Demonstration of a linear composition gradient during water saturation of CO2 in supercritical fluid chromatography

Abstract

Water was added to CO2 by saturation to increase the solvation power of the mobile phase in supercritical fluid chromatography. The saturation was performed at a temperature above the boiling point of water (100°C) to increase the amount of water which could be loaded homogeneously into the CO2 (2.5–3.0 mol% water as compared to about 0.25 mol% water at 25°C). A linear composition of water was produced by altering the density of the CO2 during saturation. Modifications to the injector and CO2 transfer lines prevented phase separation as a result of the instrumentation used in capillary supercritical fluid chromatography (SFC). After fitting vapor-liquid equilibria data to pressure, density, and temperature conditions, approximately 2.5–3.0 mol% of water was introduced in a linear gradient at 110°C. The effect of water on SFC performance was evaluated with standard steroid compounds. This paper provides further evidence for the need to examine vapor-liquid equilibria data prior to SFC.