Thermospray HPLC/MS: A new mass spectrometric technique for the profiling of steroids

Abstract

The analysis of various steroid classes by thermospray HPLC-MS using solvent systems containing 0.1 M ammonium acetate has been described. For simple unconjugated 3-oxo-4-ene steroids the positive ion spectra are dominated by a parent ion M + H + and with increasing numbers of hydroxyl group intense ions formed by sequential losses of water (M + H − n 18) + become important. Steroids with dihydroxyacetone side-chains readily lose these side-chains and the resulting (M + H − 60) + fragment is the base peak in their spectra. The (M + H − 60) + ion is not important for most steroids with glycerol-type side-chains. Although competition between thermal degradation and vaporization was observed at lower concentrations, the effect was minimized after optimizing conditions and the protonated molecular ion was easily detected when as little as 1–10 pmol of material were injected on-column. Steroid glucuronides when analyzed in the negative ion mode give simple spectra with base peak and parent ion (M-H) -. Lack of fragmentation permits facile and sensitive measurement of individual glucoronides by selected-ion-monitoring. Extensive fragmentation is seen in the positive ion mode with sequential losses of H 2O from the molecular ions (M+NH 4) + and from the aglycone fragment ion. For simple unconjugated steroids the sensitivity of HPLC-MS in selected-ion-monitoring mode can be excellent. When the protonated molecular ion of testosterone was monitored the signal/noise ratio for 30 pg testosterone was about 10.