Analysis of ‘legal high’ substances and common adulterants using handheld spectroscopic techniques

Abstract

The identification of 'legal highs' is challenging as they often do not match their label claim and contain a wide range of impurities and/or adulterants. In addition, there is a need for techniques to be on-site, rapid and non-destructive. The feasibility of using the in-built algorithms of handheld near-infrared (NIR), Raman and attenuated total reflectance Fourier transform-infrared (ATR-FT-IR) spectroscopy for the identification of 'legal high' substances was investigated. Spectral libraries were constructed using three substances found in 'legal highs' (i.e., dextromethorphan, 2-aminoindane and lidocaine) and their 50 : 50 mixtures with caffeine. Model dilution mixtures with caffeine (i.e., 5-95% m/m) and seven 'legal high' Internet products were used to test the method. The 'legal high' constituents in most of the model mixtures were identified within a minimum range of 30-60% m/m for NIR, 20-75% m/m for Raman, and 41-85% m/m for ATR-FT-IR. This demonstrates that simple library mixtures could be used to identify test substances when the concentrations are variable. Below and above these levels, the test mixtures often correlated to the component in higher concentration. Collectively, the instruments identified the main constituents in the seven Internet products with varying correlation criteria. The NIR and ATR-FT-IR provided complementary information compared to Raman when carbohydrate cutting agents were added to the product, yet the Raman showed a high fluorescence signal for three products hindering identification.These initial studies indicate the suitability of three complementary techniques for rapid identification of 'legal high' products. Further development of spectral libraries, algorithms, and use of alternative Raman excitation wavelengths is needed to provide adequate tools for in-field analysis by non-experts.

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

“…There was a correlation to MCC (77.4 ± 0.2 %) for P18 even though 5-APB was present in the sample, this suggests that the cutting agent concentration was in a higher proportion compared to the active ingredient. [31] In the case of P20, a 60 ± 4 % correlation to 5-APB was found as no 5-MAPB signature was present in the Raman library. This demonstrates that a substance may be correlated to a similar structural analogue using the algorithm, which can assist with identifying suspect NPS.…”

“…[38] From these studies, a challenge when using Raman to analyse NPS 'street samples' was fluorescence, often resulting from impurities and/or cutting agents, which can mask the signal from the active ingredients in the product. [31,39,40] Goodacre and coworkers investigated the use of surface enhanced Raman spectroscopy (SERS) to enhance the Raman signal while also reducing interference due to fluorescence. [36,37] Although SERS is a viable approach for fluorescence reduction, careful and invasive sample preparation is often needed.…”

“…The use of Raman spectroscopy may overcome these challenges as it offers a number of advantages for in-field testing such as high discrimination power, [29] minimal to no sample preparation, through package analysis, and low sensitivity to moisture, physical properties [30] and cutting agents. [31] A recent study evaluated the use of hand-held FT-IR, NIR and Raman spectrometers for NPS analysis, where Raman spectroscopy preformed the best when identifying the components in model mixtures. [31] Although the UNODC does not report on the use of Raman spectroscopy for NPS characterisation, [1] it is considered a Category A forensic technique.…”

“…[31] A recent study evaluated the use of hand-held FT-IR, NIR and Raman spectrometers for NPS analysis, where Raman spectroscopy preformed the best when identifying the components in model mixtures. [31] Although the UNODC does not report on the use of Raman spectroscopy for NPS characterisation, [1] it is considered a Category A forensic technique. [29] For that reason, Raman analysis has been employed in research and forensic analysis [32] for the characterisation of drugs of abuse such as 3,4-methylenedioxy-N-methylamphetamine (MDMA), cocaine and heroin.…”

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, ).…”