sumptive identification. This is followed by gas chromatography-mass spectrometry (GC-MS), in which chromatography separates the drug from any diluents or excipients, and then mass spectrometry is used to identify the drug. This is the near universal test for identifying unknown substances. Marijuana is an exception, because it is identified normally through a sequence of tests—a presumptive color test, followed by low-powered microscopic identification, and finally by thin-layer chromatography.

Reporting of Results

Most drug chemists produce terse reports for attorneys and courts. The reports contain administrative data and a short description of the evidence. The weight or number of exhibits is stated and then the results of the analysis. A typical report for a marijuana case might read as follows:


Item 1—a sealed plastic bag containing 25.6 g of green-brown plant material.


The green-brown plant material in item 1 was identified as marijuana.

Some laboratories might mention the tests that were conducted, but in most cases the spectra, chromatograms, and other evidence of the analysis and the chemist’s notes are not submitted. Likewise, possible sources of error and statistical data are not commonly included. From a scientific perspective, this style of reporting is often inadequate, because it may not provide enough detail to enable a peer or other courtroom participant to understand and, if needed, question the sampling scheme, process(es) of analysis, or interpretation.

Summary Assessment

The chemical foundations for the analysis of controlled substances are sound, and there exists an adequate understanding of the uncertainties and potential errors. SWGDRUG has established a fairly complete set of recommended practices.16 It also provides pointers to a number of guidelines for statistical sampling, both for illegal drugs per se (created by the European Network of Forensic Science Institutes) and for materials more generally (created by the American Society for Testing and Materials).

The SWGDRUG recommendations include a menu of analytical chemistry techniques that are considered acceptable in certain circumstances. Because this menu was constructed to be applicable worldwide, it includes

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