Electrospray and atmospheric pressure chemical ionization tandem mass spectrometric behavior of eight anabolic steroid glucuronides

Abstract

Mass spectrometric and tandem mass spectrometric behavior of eight anabolic steroid glucuronides were examined using electrospray (ESI) and atmospheric pressure chemical ionization (APCI) in negative and positive ion mode. The objective was to elucidate the most suitable ionization method to produce intense structure specific product ions and to examine the possibilities of distinguishing between isomeric steroid glucuronides. The analytes were glucuronide conjugates of testosterone (TG), epitestosterone (ETG), nandrolone (NG), androsterone (AG), 5α-estran-3α-ol-17-one (5α-NG), 5β-estran-3α-ol-17-one (5β-NG), 17α-methyl-5α-androstane-3α,17β-diol (5α-MTG), and 17α-methyl-5β-androstane-3α,17β-diol (5β-MTG), the last four being new compounds synthesized with enzyme-assisted method in our laboratory. High proton affinity of the 4-ene-3-one system in the steroid structure favored the formation of protonated molecule [M + H] + in positive ion mode mass spectrometry (MS), whereas the steroid glucuronides with lower proton affinities were detected mainly as ammonium adducts [M + NH 4] +. The only ion produced in negative ion mode mass spectrometry was a very intense and stable deprotonated molecule [M − H] −. Positive ion ESI and APCI MS/MS spectra showed abundant and structure specific product ions [M + H − Glu] +, [M + H − Glu − H 2O] +, and [M + H − Glu − 2H 2O] + of protonated molecules and corresponding ions of the ammonium adduct ions. The ratio of the relative abundances of these ions and the stability of the precursor ion provided distinction of 5α-NG and 5β-NG isomers and TG and ETG isomers. Corresponding diagnostic ions were only minor peaks in negative ion MS/MS spectra. It was shown that positive ion ESI MS/MS is the most promising method for further development of LC-MS methods for anabolic steroid glucuronides.