title: Optimization of silylation using N-methyl-N-(trimethylsilyl)-trifluoroacetamide, N,O-bis-(trimethylsilyl)-trifluoroacetamide and N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide for the determination of the estrogens estrone and 17alpha-ethinylestradiol by gas chromatography-mass spectrometry.
abstract: This paper reports an improved silylation procedure for simultaneous determination of the steroid hormones 17alpha-ethinylestradiol (EE2) and estrone (E1) using gas chromatography-mass spectrometry (GC-MS). This follows a re-assessment of some of the popular silylation procedures using N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), N-O-bis-(trimethylsilyl)-trifluoroacetamide (BSTFA) and N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA), which lead to the formation of trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) derivatives. Silylation of EE2 using MSTFA or BSTFA+1% TMCS in ethyl acetate, acetonitrile and dichloromethane solvents produced multiple peaks corresponding to TMS-E1, and 3-mono-TMS-EE2 and/or 3,17-di-TMS-EE2 in variable proportions depending on the solvent used. When pyridine or dimethyl formamide solvents were used in the silylation of EE2 under the same reaction conditions, only 3,17-di-TMS-EE2 derivative was formed. Derivatization using MTBSTFA reagents using ethyl acetate, acetonitrile, dichloromethane, pyridine and dimethyl formamide resulted in almost 100% conversion of mono-TBS-EE2 to the TBS-E1. Therefore, typical methods used in some previous GC-MS determinations of E1 and EE2 in environmental water and/or sediment samples are subject to speculation. However, we can confirm that any of the TMS reagents can be used with either pyridine or dimethyl formamide under suitable reaction conditions.
authors.affiliation: Colloid and Environmental Chemistry Laboratory, La Trobe University, Bendigo, Vic. 3552, Australia. a-shareef@dhinet.net.mv
authors.forename: Ali
authors.initials: A
authors.lastname: Shareef
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Angove
authors.forename: John D
authors.initials: JD
authors.lastname: Wells
mesh_terms: D000081:Acetamides; D004970:Estrone / Q000031:analogs & derivatives / Q000032:analysis*; D004997:Ethinyl Estradiol / Q000031:analogs & derivatives / Q000032:analysis*; D005463:Fluoroacetates; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D017646:Organosilicon Compounds / Q000737:chemistry; D014269:Trifluoroacetic Acid / Q000737:chemistry; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
chemical_list: D000081:Acetamides; D005463:Fluoroacetates; D017646:Organosilicon Compounds; D014297:Trimethylsilyl Compounds; C086665:N-methyl-N-(trimethylsilyl)trifluoroacetamide; D004970:Estrone; D004997:Ethinyl Estradiol; C047270:N,N-bis(trimethylsilyl)-2,2,2-trifluoroacetamide; C059151:N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide; D014269:Trifluoroacetic Acid