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Sourcing Organic Compounds Based on Isotopic Variation

High Precision Isotope Ratio Mass Spectroscopy (IRMS)

! Instrumentation

IRMS instruments are highly specialized for the analysis of

1 3 C / 1 2 C , 2 H / 1 H , 1 5 N /

14

N,

18

O/

16

O, and

34

S/

32

S via

analysis gases CO2, H2, N2, and SO2 using a tight electron impact ion source, high transmission magnetic sector,

and multiple collectors, delivering relative standard deviations of less than 0.01%

! Isotopic Fractionation as a Fingerprinting Technique

Studies over 50 years have shown that isotopic fractionation due to physiological processes, specifically CO2 transport processes within plants and photosynthesis, leads to variation in isotope ratio in natural compounds

Sourcing Organic Compounds Based on Isotopic Variation

! Synthetic versus Natural Steriods

Synthetically-derived steroids show lower !13C than their analogues in the human body since they are synthesized using starting materials that are extracted from plants with low 13C content, mostly soy.

Endogenous steroids originates from cholesterol that is part of the human diet and are less depleted in 13C.

The differences in the 13C ratios between endogenous

and exogenous steroids are used today to directly detect the abuse of anabolic steroids with GCC-IRMS

! Detection of Synthetic Steriods

!13C ratio before and after administration of exogenous

testosterone metabolites:

5"#adiol: -24.78 to -27.04%

-28.40 to 33.35%

5$#adiol: -23.68 to -27.31%

-28.53 to 31.24%

The differences between the !13C of 5"-adiol and 5$-adiol for the individual subjects were not bigger than 1.8 -1.9% before the testosterone administration and not smaller than 3.9 - 3.6% after testosterone was given. The maximum differences after administration of testosterone were 8.2 and 7.7% respectively

Aguilera, etal: J. Chromatogr. B Biomed. Sci. Appl., 1999,727, 95.

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