Rapid detection of psychoactive and new psychoactive substances using qualitative color tests: chemistry, techniques, and applications

Abstract

This review may serve as a guide to develop technical and analytical guidelines for the selection and application of color test screening protocols for the detection of psychoactive substances (PSs), including new psychoactive substances (NPSs), to support their rapid identification or confirmation by competent authorities and users, particularly in the context of seizure and control procedures, thereby helping to mitigate the risks of intoxication and reduce the harm associated with their consumption. Given the global increase in the use of PSs and the rapid emergence of NPSs, these compounds pose critical challenges that require simple and rapid identification tools, such as colorimetric tests. These tests include Marquis, Mecke, Mandelin, Ehrlich, Duquenois–Levine, Zwikker, Froehde, Scott, nitric acid, ferric chloride, Simon, Dille–Koppanyi, Liebermann, Chen–Kao, Zimmermann, Hofmann, and Robadope. They operate through specific chemical reactions with key functional groups for presumptive identification. Each test is meticulously described, including its reagent formulations, preparation procedures, and applicability for detecting PSs and NPSs. The characteristic colors observed upon interaction with PSs or NPSs are also detailed, along with the underlying chemical reactions. However, the efficiency of this screening depends on the absence of adulterants with structures analogous to PSs and NPSs as well as on the absence of matrix effects in complex samples, where chromatic interferences can distort results and compromise analytical sensitivity. Given this complexity, integrating colorimetric testing into monitoring protocols optimizes regulatory control and facilitates access to chemical information. This transforms the analysis into an evidence-based care and prevention tool.