Page 189 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

1522_C04.fm Page 172 Thursday, November 13, 2003 9:54 AM

5
8
0
Delta 15-N −10 1
−5

−15 13
2 9
−20
−30 −29 −28 −27
Delta 13-C
Figure 4.8 Further characterization of confiscated MDMA samples using both
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d C and d N values (From Mas, F. et al., Forensic Sci. Int., 71, 225, 1995. With
15
permission.)
4.4.4 Antidoping Testing
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A major area of interest recently in the antidoping testing community is C-
content determination. This interest derived from the desire to develop a
subjective parameter for detecting misuse of androgens, especially testoster-
one. Since testosterone concentration varies among individuals, the testoster-
one/epitestosterone (the 17a epimer and metabolite of testosterone) (T/E)
ratio was used as an indirect marker of testosterone administration. Since
the T/E ratio also varies among individuals and epitestosterone can be admin-
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istered to circumvent this detection mechanism, determination of C con-
tents in testosterone and epitestosterone is now considered the most effective
approach. The effectiveness of this approach is based on the fact that synthetic
androgens are generally made from a single plant species, which have lower
13 C contents than those derived from endogenous sources.
Several studies have been carried out to use metabolic-pathway related
13 C isotope patterns to differentiate between endogenous human testosterone
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and exogenous testosterone. In the human body, testosterone is synthesized
from cholesterol via dehydroepiandrosterone and is then further metabolized
to androstanediol. Becchi, Aguilera and coworkers found that the averaged
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d C-values for endogenous 5a- and 5b-androstanediol dropped from
–26.52‰ before synthetic testosterone administration (natural background
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or baseline value) to –32.44‰ during testosterone administration. Inde-
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pendent work by Shackleton et al. obtained a similar baseline d C-value of
–26.87‰ and a drop down to –30.21‰ on average for androstanediol sam-
ples after a bolus administration of 250 mg exogenous testosterone. 84,85 This
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drop of about –4‰ lasted for up to 10 d before d C values of androstanediol
returned to their former baseline value. They also reported a narrow range
of –29.15 to –30.41‰ for 5 synthetic testosterone samples manufactured in
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5 different countries. Based on the results reported by Aguilera et al. and
their own, Shackleton et al. suggested a conservative cut-off value of –29.0‰

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