DEMONSTRATION OF A LINEAR COMPOSITION GRADIENT DURING WATER SATURATION OF CO2 IN SUPERCRITICAL-FLUID CHROMATOGRAPHY

Water was added to CO2 by saturation to increase the solvation power o f the mobile phase in supercritical fluid chromatography. The saturati on was performed at a temperature above the boiling point of water (10 0-degrees-C) to increase the amount of water which could be loaded hom ogeneously into the CO2 (2.5-3.0 mol% water as compared to about 0.25 mol% water at 25-degrees-C). A linear composition of water was produce d 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 c hromatography (SFC). After fitting vapor-liquid equilibria data to pre ssure, density, and temperature conditions, approximately 2.5-3.0 mol% of water was introduced in a linear gradient at 110-degrees-C. The ef fect of water on SFC performance was evaluated with standard steroid c ompounds. This paper provides further evidence for the need to examine vapor-liquid equilibria data prior to SFC.