تسجيل الدخول

تسجيل

Isotope ratio mass spectrometry

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  277

2026-10-24

25

Isotope ratio mass spectrometry

Combustion isotope ratio MS (CIRMS) is now used routinely by some WADA accredited laboratories. After injection, the sample flows through the column and the compounds of interest are separated on the column. Eluted compounds are then combusted oxidatively in a combustion reactor. Nitrogen oxides are removed by reduction to nitrogen and water is then removed by passing the eluent through a water separator. The sample is then introduced into the ion source of the MS by an open split interface. CIRMS provides an additional tool to help distinguish a person whose testosterone to epitestosterone ratio may be naturally beyond the normal range from an individual who has administered testosterone. The synthetic testosterone has a different proportion of 13C to the more abundant 12C than the normal endogenous steroid (de la Torre et al. 2001). The extracted steroids are separated by GC and then converted into CO₂ and the relative amounts of 12C to 13C as CO₂ determined for each eluting steroid in turn. Typically, the testosterone metabolites androsterone and etiocholanolone or androstanediols are monitored (Aguilera et al. 2000), or the metabolites 5a-androstanediol and 5b-androstanediol (Shackleton et al. 1997b; Aguilera et al. 2001), often comparing the results with pregnanediol or pregnanetriol as endogenous internal standards (Shackleton et al. 1997a; Aguilera et al. 1999). Aguilera et al. (1997) have also used GC-CIRMS to detect exogenous hydrocortisone administration to the horse.