Identification of new psychoactive substances (NPS) using handheld Raman spectroscopy employing both 785 and 1064 nm laser sources

Abstract

The chemical identification of new psychoactive substances (NPS) in the field is challenging due not only to the plethora of substances available, but also as a result of the chemical complexity of products and the chemical similarity of NPS analogues. In this study, handheld Raman spectroscopy and the use of two excitation wavelengths, 785 and 1064 nm, were evaluated for the identification of 60 NPS products. The products contained a range of NPS from classes including the aminoindanes, arylalkylamines, benzodiazepines, and piperidines & pyrrolidines. Identification was initially assessed using the instruments' in built algorithm (i.e., % HQI) and then further by visual inspection of the Raman spectra. Confirmatory analysis was preformed using gas chromatography mass spectrometry. For the 60 diverse products, an NPS was successfully identified via the algorithm in 11 products (18 %) using the 785 nm source and 29 products (48 %) using the 1064 nm source. Evaluation of the Raman spectra showed that increasing the excitation wavelength from 785 to 1064 nm improved this 'first pass' identification primarily due to a significant reduction in fluorescence, which increased S/N of the characteristic peaks of the substance identified. True positive correlations between internet products and NPS signatures ranged from 57.0 to 91.3 % HQI with typical RSDs < 10 %. Tablet formulations and branded products were particularly challenging as a result of low NPS concentration and high chemical complexity, respectively. This study demonstrates the advantage of using a 1064 nm source with handheld Raman spectroscopy for improved 'first pass' NPS identification when minimal spectral processing is required, such as when working in field. Future investigations will focus on the use of mixture algorithms, effect of NPS concentration, and further improvement of spectral libraries.

Identification of new psychoactive substances (NPS) by Raman spectroscopy

“…Interference by fluorescence or a very noisy spectrum with the 785 nm laser was observed for 16 out of the 31 samples analysed. This would not allow establishing a routine for classifying or identifying drugs of abuse as it was already mentioned . In some other cases, the spectra obtained with the 785 and 1064 nm laser were in good agreement even though fluorescence resulting from the sample containers (glass vial) in which the measurements were performed was observed (results not shown).…”

“…These three families of substances were selected in this study because there is an urgent need of developing a fast, nondestructive, and cheap analytical method for their detection in the field due to the considerable harms and risks they can produce. Raman spectroscopy has been chosen for this purpose because it has been demonstrated to be a very valuable technique to discriminate NPS . Moreover, as mentioned by Zloh et al, it is essential to explore effective ways of identifying and classifying existing and emerging NPS.…”

“…The main challenge when analysing NPS samples can be the high fluorescence due to impurities . Previous studies that reported on the use of handheld Raman devices equipped with different laser excitation wavelengths for the identification of a range of commercially available NPS recommended the use of 1064 nm systems or dual laser devices (785 and 1064 nm) to achieve sensitive detection with low/no fluorescence frequently observed when using 785 nm lasers.…”

Intended and unintended use of cathinone mixtures

“…Adulterants and cutting agents may have similar chemical structures to target drugs in order to add to the complexity of the mixture (Noonan, Tonge, Fenton, Damiano, & Frederick, ; Ryder, ; Ryder, O'Connor, & Glynn, ) and may have a stronger or masking detection signal that the target NPS and hence may hinder identification (Assi, Guirguis, Sheelagh, Fergus, & Stair, ; Guirguis et al, ). Typical examples includes the similarity in the chemical structures of nicotinamide and cathinone, stronger detection signal of benzocaine (Guirguis et al, ), or masking signal of impurities (e.g., dyes or cutting agents such as microcrystalline cellulose; Assi et al, ; Guirguis et al, ). In 2014, adulterants over which UK law enforcement agencies have gained power to seize if they suspect that they are used for cutting NPS included lidocaine, benzocaine, and phenacetin (Home Office, ).…”

“…In Poland, two-thirds of buphedrone samples seized by a law-enforcement raid in 2010 were found to contain 4-MEC and MDPV (Zuba, Adamowicz, & Byrska, 2013). In a large study investigating 60 NPS purchased over the internet during 2012-2013, a product sold as (2-aminopropyl) benzofuran was found to contain 5-(2aminopropyl) benzofuran and pyrovalerone (Guirguis, Girotto, Berti, & Stair, 2017).…”