Formation of multiple trimethylsilyl derivatives in the derivatization of 17α-ethinylestradiol with BSTFA or MSTFA followed by gas chromatography-mass spectrometry determination

Sate Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Journal of Environmental Sciences (Impact Factor: 2). 02/2007; 19(7):879-84. DOI: 10.1016/S1001-0742(07)60146-6
Source: PubMed


N,O-bis(trimethylsily)trifluoroacetamide (BSTFA) and N-methyl-N(trimethylsily) trifluoroacetamide (MSTFA) are common derivatization reagents used in the GC-MS analysis of estrogen steroids such as estrone (El) and 17alpha-ethinylestradiol (EE2). In this study, three trimethylsilyl (TMS) steroid derivatives, mono- and di-trimethylsilyl EE2 and mono-trimethylsilyl E1, were observed during the derivatization of EE2 with BSTFA or MSTFA and/or GC separation. Factors influencing the production of multiple TMS derivatives and their relative abundance were examined. It was found that both methanol and bisphenol A competed with estrogenic esteroids when reacting with silylation reagents, and thus affected the formation of TMS derivatives and their relative abundance in the derivatization products. Methanol was found to be more reactive than bisphenol A with the BSTFA reagent. None of the three solvents tested in this study could prevent the generation of multiple TMS derivatives during the derivatization of EE2 with BSTFA, followed by GC analysis. A similar result was observed using MSTFA as the derivative reagent followed by GC analysis. Thus, the suitability of BSTFA or MSTFA as the derivatization reagent for the determination of E1 and EE2 by GC-MS, under the conditions reported here, is questionable. This problem can be solved by adding trimethylsilylimidaz (TMSI) in the BSTFA reagent as recommended, and the performance of the method has been proved in this study.

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    • "Prior GC/MS analysis is necessary to carry out steroid derivatization to increase the volatility and thermal stability of the molecules and to improve chromatographic separation and detection. For GC, the preferable derivatization technique remains silylation [Zhou et al., 2007] and most frequently used reagents include N,O-bis(trimethylsilyl), trifluoroacetamide, and N-methyl-N-trimethylsilyltrifluoroacetamide, trimethyliodosilane , trimethylsilylimidazole, and trimethylchlorosilane . Derivatization is aimed at the formation of alkylsilyl derivatives through displacement of active protons in –OH or -NH groups. "
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    • "The eluate was concentrated, derived with BSTFA/TCMS/TMSI (99:1:0.5, v/v/v). The separation and detection of the target compounds were achieved by GCeMS using selected-ion mode based on the method from Zhou et al. (2007) "
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