LARGE-VOLUME INJECTION IN CAPILLARY SUPERCRITICAL FLUID CHROMATOGRAPHY

A system was developed to introduce large sample volumes (100 muL or more) into a capillary supercritical fluid chromatograph (SFC). Capillary columns of 50-mum internal diameter (i.d.) were used without a noticeable decrease in chromatographic efficiency and resolution. The sample introduction system consisted of a series of valves which were operated to effect sampling into an inlet column, followed by a solvent elimination step. A SF extraction step was then used to refocus the analytes at the head of the capillary SFC column. Chromatography of the refocused analytes was accomplished with pressure programming of the CO2 mobile phase. Narrow bands were obtained in the final SFC analytical step for a variety of analytes including alkanes, synthetic triglycerides, polymer additives, and polyglycols in solvents such as methylene chloride, chloroform, acetonitrile, and water. A peak with greater than a ten to one signal to noise ratio was obtained for a 100-muL injectio of a 10 parts per billion (ppb) solution of tribehenin (C22:0) using flame ionization detection (FID). Triton X-100 in water was analyzed at the 3 ppm level using a 100-muL injection. Injection reproducibility at 1 ppm for 10-muL injection of Irganox 1076 polymer additive was 0.16% relative, based on the raw peak areas. The large-volume injection system described allowed sensitivity increases of 1000-fold, coupling with liquid chromatography, injection of a large variety of advents, including water, and a 10-fold improvement in reproducibility.