title: Artifact formation due to ethyl thio-incorporation into silylated steroid structures as determined in doping analysis.
abstract: Trimethylsilylation of target substances in a mixture of N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), ammonium iodide and ethanethiol is frequently applied for the application of gas chromatography-mass spectrometry (GC-MS) in steroid analysis. However, artifacts were formed when using this mixture to silylate the steroids androsterone and etiocholanolone obtained from a urine matrix. The artifacts were identified as ethyl thio-containing products of the respective trimethylsilyl derivatives. The conversion of the studied products increased slowly as a function of time, was dependent on the presence of the urine matrix and was significantly accelerated by adding diethyl disulfide to the reagent before incubation. Also ethyl thio-incorporation into testosterone and epitestosterone was established. A mechanism for ethyl thio-incorporation is proposed. The conversion achieved after 120-h sample storage at room temperature was insufficient to significantly influence the analysis of androsterone and etiocholanolone under the studied conditions. However, the results provide fundamental insight into the mechanism of silylation and the occurring side-reactions. Moreover, when investigating the formation of new metabolites, the ethyl thio-incorporation can lead to misinterpretation.
authors.affiliation: Department of Human Toxicology, Utrecht Institute of Pharmaceutical Sciences (UIPS), University of Utrecht, The Netherlands. d.h.vandekerkhof@pharm.uu.nl
authors.forename: D H
authors.initials: DH
authors.lastname: van de Kerkhof
authors.forename: R D
authors.initials: RD
authors.lastname: van Ooijen
authors.forename: D
authors.initials: D
authors.lastname: de Boer
authors.forename: R H
authors.initials: RH
authors.lastname: Fokkens
authors.forename: N M M
authors.initials: NM
authors.lastname: Nibbering
authors.forename: J W
authors.initials: JW
authors.lastname: Zwikker
authors.forename: J H H
authors.initials: JH
authors.lastname: Thijssen
authors.forename: R A A
authors.initials: RA
authors.lastname: Maes
mesh_terms: D016477:Artifacts; D004300:Doping in Sports; D012821:Silanes / Q000737:chemistry*; D013256:Steroids / Q000737:chemistry / Q000652:urine*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D012821:Silanes; D013256:Steroids; D013438:Sulfhydryl Compounds; C007638:ethanethiol