Page 185 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

1522_C04.fm Page 168 Thursday, November 13, 2003 9:54 AM

a mass discrimination (= isotopic fractionation) favoring the heavier iso-
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topes. For C, moving up in the food chain by 1 level is associated with bulk
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d C values in the feeding organism to be 1 to 3‰ higher (i.e., more enriched
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in C) as compared to those found in its diet. The same is true for d N
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values; here the trophic mass discrimination leads to bulk d N values being
generally higher by 2 to 4‰. As a matter of fact, this relation of isotopic
fraction and feeding level can be exploited to prove that salmon sold as wild
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salmon is indeed wild and not farmed. Bulk d C values of wild salmon should
be of the order of –16 to –17‰, i.e., 2 to 3‰ higher than its favorite food,
crustaceans (e.g., prawns) that shows bulk d C values of about –19 to –20‰.
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In contrast, farmed salmon usually exhibits bulk d C values of –22 to –23‰
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thus betraying its origin. So, finding a difference in the isotopic composition
of diet and feeding organism is (1) expected and (2) a very useful analytical
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tool. This is further confirmed by a recent study on two strains of bacteria
(Bacillus globigii and Erwinia agglomerans). 69

4.4.3 Drugs

Drug sample differentiation based on natural stable isotope variation can
rely on isotope composition determination in the bulk sample or in specific
compounds. These approaches are more commonly used to differentiate
products from different geographical regions. It has also been advocated to
differentiate products from different manufacturing batches.

4.4.3.1 Marijuana
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Data shown in Table 4.4 show variations in C/ C ratios derived from the
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combustion of bulk marijuana samples. These results indicate that ambient
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air seems to control the isotopic composition of the plant. The C content
in the samples analyzed decreases in the order of A, B (from rural area), C
(from metropolitan area), D, F (indoor plant). This order coincides with the
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order of the C content in the ambient air under which these plants are
grown. Since a heater using natural gas containing less-than-usual amounts
of C is used in the greenhouse, the carbon dioxide inside the greenhouse
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would be the lightest. The reabsorption of carbon dioxide derived from plants
confined in the greenhouse might have led to further depletion in C con-
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tent. Due to the heavy use of petroleum products, it seems reasonable to
assume that the C content in metropolitan areas are less than that of rural
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areas. Whether the difference in samples D (a male plant) and F (a female
plant) is due to sex difference is not certain as the origin of the seeds is not
well established. This preliminary study certainly provides interesting infor-
mation, but a more extended survey and more specific analysis of pure
chemical components are needed for better understanding.

© 2004 by CRC Press LLC