Creating an Aqueous Precipitation and Crystal Table for Microcrystal Tests of Common Illicit Drugs

When it comes to preliminary testing in forensic science laboratories, a method that is simple, fast, reliable, inexpensive, and non-destructive is desirable. Most methods only fulfill a few of these requests or require complex instrumentation. Microcrystal tests not only meet these requirements, but they also only need a polarized light microscope (which most forensic science laboratories already own). It provides an easy way to test for commonly abused drugs that are found in many different forms. To help make microcrystal test methods more accessible, McCrone Research Institute published “A Modern Compendium of Microcrystal Tests” which provides thirty-four different methods to test for twenty-one drugs. The methods in this compendium had never been cross checked with every drug so it was not known if the crystals were truly unique. This led to a need to test every method with every drug in the compendium. After the completion of testing, the data generated was used to create an aqueous precipitation and crystal table. At first glance this table showed that not every crystal cited in the compendium was unique to a specific drug. By observing all the optical properties that can be obtained by using a polarized light microscope however, the crystals formed by different drugs were still distinguishable from one another for most of the methods. The methods using picric acid to test for methylphenidate and dilituric acid to test for pseudoephedrine were shown to produce indistinguishable crystals for multiple drugs when using fast and reliable methods. More complex testing allows for an identification, but this would go against the point of using a microcrystal test as a preliminary means of identification. Looking at the aqueous precipitation and crystal table, thirty-two of the thirty-four methods produced unique crystals and some combination of these methods still allows for an identification of all twenty-one drugs. The aqueous precipitation and crystal table also proves to be a great identification tool for use in testing.