Portable Near Infrared Spectroscopy for the Isomeric Differentiation of New Psychoactive Substances

Rapid and efficient identification of the precise isomeric form of new psychoactive substances (NPS) by forensic casework laboratories is a relevant challenge in the forensic field. Differences in legal status occur for ring-isomeric species of the same class, thus leading to different penalties and judicial control. Portable systems such as near-infrared (NIR) spectroscopy recently emerged as suitable techniques for the on-scene identification of common drugs of abuse such as cocaine, MDMA and amphetamine. This way, the overall forensic process becomes more efficient as relevant information on substance identity becomes available directly at the scene of crime. Currently, no NIR-based applications exist for the rapid, on-scene detection of NPS isomers. Herein, we present the differentiation of cathinone and phenethylamine-type NPS analogues based on their NIR spectrum recorded in 2 seconds on a portable 1350 - 2600 nm spectrometer. A prior developed data analysis model was found suitable for the identification of the methylmethcathinone (MMC) isomers 2-MMC, 3-MMC and 4-MMC. In 51 mixtures and 22 seized casework samples, the correct isomeric form was detected in all cases except for a few mixtures with an active ingredient content of 10 wt%. These results show the feasibility of on-site NPS detection as presumptive test performed directly at the scene of crime with a small size NIR-spectrometer. Additionally, in the illicit drug analysis laboratory the combination of NIR and GC-MS analysis might be suitable for robust identification of NPS isomers and analogues.

2 nd derivative NIR spectra of cathinone isomeric sets of Figure 1, overlay of 5 replicates for each isomer form.Figure S2.
2 nd derivative NIR spectra of MDMA analogues of Figure 2, overlay of 5 replicates for each isomer form.Figure S3.
Identification results of the cathinone drug-isomer mixtures.Table S3.
Identification results of MMC/MEC containing casework samples in glass vials.Figure S5.
FTIR spectra of 4-MMC HCl, case sample MM006, and case sample MM006 after heating.Table S4.
Identification results of MMC/MEC containing casework samples in plastic bags.Note.The result in orange indicates that one of the two isomers is missed, results in gray on library options 1 and 3 are not relevant because they don't allow the detection of multiple drugs in a mixture.These are presented for information only.
Table S3.(part 1 of 2) Identification results of MMC/MEC containing casework samples in glass vials.
Note. Results in red indicate erroneous identifications, results in gray are below threshold and considered inconclusive.Results on library option 2 (multiple drug mixtures allowed) are presented for information only.Instrument: PerkinElmer (Waltham, MA) Spectrum Two FTIR with ATR option, scan range 400 to 1400 cm −1 .

Table S1 .
(part 4 of 4) Identification results of the 0 wt% -100 wt% diluted cathinone mixtures.Note.Results in red indicate erroneous identifications, results in gray on library options 2 (multiple drug allowed) and 3 (including both hydrated and anhydrous 4-MMC) are presented for information only.

Table S2 .
Identification results of the cathinone drug-isomer mixtures.