Structural Core Discrimination of Emerging Synthetic Cannabinoids: A Presumptive Colorimetric Test

Abstract The continuous structural modifications of new psychoactive substances (NPS), particularly synthetic cannabinoids (SCs), present significant analytical challenges in their rapid identification. Following the discovery of a novel third-generation SC in seized herbal material with no matches in national databases, a simple analytical approach based on core structure recognition was developed. An effective yet straightforward colorimetric assay was developed to distinguish structural cores of SCs through their distinctive fluoride reactions. This method can clear distinguish between SCs containing isatin cores and those with indole or indazole moieties due to their distinct spectroscopic signatures. The method was validated against reference standards, demonstrating a strong linear relationship ( R 2 = 0.9998), high precision (relative standard deviation (RSD) < 2%), low detection limit (2.89 µM), and quantitative recovery (> 101%) from herbal matrices. To our knowledge, this is the first approach to identifying core structures of SCs prior to mass spectrometry analysis of unknown compounds, significantly streamlining their structural elucidation. Moreover, the net colour changes produced enable reliable, rapid detection of the compounds with the naked eye at concentrations representative of those found in seized herbal materials, making the method suitable for both forensic laboratories and rapid on-site screening by law enforcement agencies. This approach offers an effective solution for presumptive testing of emerging SC variants in both laboratory and field settings.