Gas chromatography-combustion-isotope ratio mass spectrometry analysis of 19-norsteroids: application to the detection of a nandrolone metabolite in urine

Determination of whether the major metabolite of nandrolone in urine, 19-no randrosterone (19-NA), is exogenous or endogenous in origin is one of the m ost exciting challenges for antidoping laboratories. Gas chromatography-com bustion-isotope ratio mass spectrometry (GC-C-IRMS) can be used to differen tiate these two origins by carbon isotopic ratio analysis. A complete metho d for purification of 19-NA in urine has been established. Acetylated ketos teroids, and in particular 19-NA, are isolated from the urine matrix before analysis after hydrolysis and purification of urine by reversed-phase and normal solid-phase extraction. The limit of detection for 19-NA was about 6 0 ng with recoveries of 54-60%. Evidence of exogenous administration of 19- NA may be established from isotope ratio determination from the C-13/C-12 r atios of several synthetic 19-norsteroids compared to those obtained for en dogenous steroids. (C) 2001 Elsevier Science B.V. All rights reserved.