CHAPTER 10: Light in Forensic Science: Microcrystalline Tests of New Psychoactive Substances Using Light Microscopy

Microcrystalline tests are chemical tests carried out under the light microscope that can be used to detect a range of analytes including drugs of abuse. Specific microcrystals form when the drug and a reagent are combined within a micro-drop. In this chapter, microcrystalline tests are presented for the group of drugs known as New Psychoactive Substances (NPS). The emergence and proliferation of NPS presents a major challenge for drug analysis laboratories who need to respond quickly in developing new analytical methods. Specific microcrystalline tests can easily be developed for NPS as shown by the examples presented in this chapter. Tests for gamma-hydroxybutyrate, benzylpiperazine, 3,4-methylenedioxy-2-aminoindane (MDAI) and mephedrone (4-MMC) are presented with each showing distinctive microcrystals recorded as photomicrographs. When viewed under polarising light additional features are seen which further adds to the discrimination of the test. Mercury(ii) chloride is a versatile test reagent, often utilized as the starting point when developing new microcrystalline tests. It is shown that when mixtures of MDAI and caffeine are tested with mercury(ii) chloride, microcrystals for both MDAI and caffeine develop in the same micro-drop. When combined with micro Raman Spectroscopy the high specificity of microcrystalline tests is demonstrated by being able to distinguish between the structural isomers of 4-MMC, 3-MMC and 2-MMC.