تسجيل الدخول

تسجيل

Some Unusual Situations

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p347-348

2026-08-10

30

Some Unusual Situations

There are some situations where the usual schemes of analysis may not be used. These occur where there is visual or other evidence that the controlled substance present is most probably of a certain type. The most common situation that illustrates this is marihuana. As was previously mentioned, marihuana is most often used by smoking the dried, crushed leaves, and flowers of the cannabis plant. This plant material has some distinctive features that can be used to help in identification. These features include the presence of cystolith hairs on one side of the leaf surface and numerous, small white hairs on the other side. The seeds of the cannabis plant are also quite distinctive in appearance. Once the drug analyst recognizes these characteristic features, then it is necessary only to show that the cannabinoid alkaloids that are associated with cannabis are present. These include THC, cannabinol, and cannabidiol, as well as others. This is accomplished by using the presumptive color test for marihuana, the Duquenois–Levine test, followed by some form of chromatography, usually TLC. The vast majority of crime laboratories throughout the world consider this scheme to be sufficient to declare that such plant material is marihuana. If the exhibit occurs as suspected hash oil, where there is virtually no plant material to identify, then this is usually treated as more of an unknown and a confirmatory test must be done. Another situation that is often treated in a different manner than the usual drug is LSD cases. Most often, LSD occurs as blotter acid—impregnated into absorbent paper, which is then eaten. There is no other controlled substance that looks like this. LSD is intensely fluorescent and measurement of the fluorescence spectrum is highly indicative of LSD or one of its known isomers such as LAMPA (lysergic acid methylpropyl amide). There is also a good presumptive color test for LSD; Ehrlich’s test. The Ehrlich’s reagent is also a good spray reagent for thin layer plates and colors LSD light purple. A combination of Ehrlich’s test, TLC, and fluorescence is consid ered a valid scheme of analysis for LSD by many laboratories. Another important exception to the confirmation rule for drugs is marked tablets and capsules. Legitimately manufactured tablets and capsules are normally marked with a logo and some identifying numbers and/or letters. The size, shape, and color of the tablet or capsule can provide valuable and helpful information about the identity of that drug. There are compendia such as the Physician’s Desk Reference that have pictures of many common tablets and capsules and which are helpful in identification. In many laboratories, such an identification coupled with one test such as TLC, is all that is needed to identify the tablet or capsule. It must be recognized, however, that there are some very good counterfeit tablets and that many capsules can be easily opened and adulterated, so the physical identification is not enough for forensic confirmation.