Analysis of steroids by capillary supercritical fluid chromatography with phosphorus-selective detection

Steroids were derivatized with dimethylthiophosphinic chloride to produce steroidal thiophosphinic esters. A catalyst, 4-dimethylaminopyridine, was used to promote quantitative and reproducible thiophosphinic ester formation at low reaction temperatures. The derivatives were analyzed by capillary supercritical fluid chromatography (SFC) with phosphorus thermionic detection. The phosphorus thermionic detector exhibited linearity over 3-4 orders of magnitude. A sensitivity of 120 fg P/s was obtained for the dithiophosphinic ester of pregnanediol at a signal-to-noise ratio of 3. The efficiency of capillary SFC and the excellent sensitivity of the phosphorus thermionic detector were demonstrated by the analysis of steroids isolated from both human urine and plasma.