Mass spectrometric analysis of 7-oxygenated androst-5-ene structures. Influence in trimethylsilyl derivative formation

Rationale Several authors have described the generation of androsta-3,5-diene-7-one structures from androst-5-ene-3,7-dione or androst-5-ene-3 beta-ol-7-one under acidic conditions and/or at high temperatures. The goal of this study was to observe and to describe the results obtained after the chromatographic analysis of the trimethylsilyl derivatives of reference materials of 7-oxo-DHEA, 7 alpha-hydroxy-DHEA, 7 beta-hydroxy-DHEA, and androsta-3,5-diene-7,17-dione known as arimistane. Methods The purity of the analyte reference materials was verified by liquid chromatography/quadrupole mass spectrometry. The trimethylsilyl derivatives obtained using several mixtures with MSTFA (N-methyl-N-trimethylsilyl trifluoroacetamide) in comparison with solely MSTFA were analyzed by gas chromatography coupled to a time-of-flight detector equipped with a multimode inlet or to a simple quadrupole detector with a split/splitless inlet. Results The study showed that the formation of arimistane from 7-oxo-DHEA occurs using common derivatization reagents used for the analyses by gas chromatography (GC). In addition, the formation of theenolizedTMS derivative of 7-oxo-DHEA was observed in considerable amount when it was reacted with MSTFA. The analysis of 7 alpha-hydroxy-DHEA resulted in the detection of similar to 1% of arimistane. The formation of unexpected artifacts from derivatization is influenced by the reagent itself, the reaction temperature, the inlet used and its configuration. Conclusions The derivatization reagent, instrumental conditions (inlet), as well as the chemical structures of the analytes present in the matrix, can influence the results. So, before describing a new feature as a potential "new" metabolite, special caution must be taken since we could actually be dealing with an artifact.