Colour quantitation for chemical spot tests for a controlled substances presumptive test database

Crime scene investigators (CSIs) often encounter unknown powders, capsules, tablets, and liquids at crime scenes, many of which are controlled substances. Because most drugs are white powders, however, visual determination of the chemical identity is difficult. Colourimetric tests are a well-established method of presumptive drug identification. Positive tests are often reported differently, however, because two analysts may perceive colour or record colourimetric results in different ways. In addition to perceiving colour differently, it is very common for there to be poor visibility conditions (e.g. rain, darkness) while performing these tests, further obscuring the results. In order to address these concerns and to create uniformity in the reporting of on-site colourimetric test results, this study has evaluated two of the state-of-the-art apps (ColorAssist® and Colorimeter®) for reporting the colour test results quantitatively in red-green-blue (RGB) format. The compiled library database of presumptive test results contains over 3300 data points including over 800 unique drug/test combinations. Variations observed between test replicates, from performing a test on different days, recording with a different device type (e.g. iPod Touch, iPhone models 4, 5c, 5s, or 6), and using different quantities of drug are discussed. Overall, the least variation in Euclidian norm was observed using ColorAssist® with the camera light (25.1±22.1) while the variation between replicates and data recorded using different devices was similar. The resulting library is uploaded to a smartphone application aimed to aid in identifying and interpreting suspected controlled substance evidence. Copyright © 2016 John Wiley & Sons, Ltd.