Chemical identification and differentiation of positional isomers of novel psychoactive substances – A comprehensive review

Due to the consistently increasing number of novel psychoactive substances (NPSs), reliable and unambiguous drug isomer identification is becoming more challenging for forensic laboratories. Currently, gas chromatography-mass spectrometry (GC-MS) is the gold standard for forensic drug substance identification. However, this technique is typically incapable of confidently differentiating positional isomers. To achieve robust identification of NPS isomers, other approaches must be utilized. The aim of this review is to provide an overview of the methods presented in the scientific literature for the differentiation and identification of NPS positional isomers. The features, advantages, and drawbacks of these methods are discussed, and a generalized workflow for routine analysis of seized NPS samples in forensic laboratories is proposed.