APPLYING THE SCIENCE 8.3 Good, Not Perfect

GCMS is central to forensic drug analysis because anai) there are compounds that have nearly identical mass spec-are separated and definitively identified by the combination tra. A partial list of compounds of forensic interest includes 

As noted in Applying the Science 8.1, there are separation techniques that wiU discriminate between enantiomers, but the mass spectra do not definitively differentiate them. As a result, instrumental confirmation of identification can be 

The most abundant ion peak in many compounds in the methamphetamine family is found at 58 amu. Mass spectra are processed by assigning the largest peak (called the base peak) a value of 100 and scaling all other peaks to that value. Consequently, many minor peaks may be all but lost. Removing the base peak and renormalizing the 

Source Steeves, J. B., et al. Normalization of Residual Ions after Removal of the Base Peak in Electron Impact Mass Spectrometry. Journal of Forensic Sciences, 45 2000,882-885. 

Unlike the situation noted for marijuana, the morphology of mushrooms and peyote is normally not used as part of their identification, due to the more complex botanical challenge. The plant-matter matrix of peyote and psilocin mushrooms makes the use of color tests impractical, unless the tests are apphed to the extract. In most cases, ethanol or methanol is the extraction solvent of choice for dried plant matter. Some laboratories heat the methanol prior to extraction. The peyote button, and sometimes mushrooms, must be grotmd with coffee grinders or similar equipment or must be macerated prior to extraction. Cleaning these appliances between uses is crucial to prevent cross-contamination. The extracts are then amenable to TLC and instrumental confirmation by GCMS. 

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