Rapid Qualitative Analysis of Synthetic Cannabinoids by Raman
Spectroscopy
HU Shuang1, LIU Cui-mei2*, JIA Wei2, HUA Zhen-dong2
1. Beijing Police College, Beijing 102202, China
2. Key Laboratory of Drug Monitoring and Control, Drug Intelligence and Forensic Center, Ministry of Public Security, Beijing
100193, China
Abstract：In July 2021, China imposed a class-wide ban on synthetic cannabinoids, with the definition of synthetic cannabinoids by seven core structures. It is an urgent need for the drug law-enforcing departments and relevant technicians to conduct in-field rapid qualitative analysis of suspected synthetic cannabinoid samples. This study investigated the overall discriminant ability of Raman spectroscopy for synthetic cannabinoids, compared four handheld Raman spectrometers, and discussed the possible reasons that restricted the wideapplication of Raman spectroscopy. ProTT-EZRaman-A7 portable Raman spectrometer, with the overall performance between desktop Raman and handheld Raman, was selected to collect the Raman spectra of 90 synthetic cannabinoid reference substances. Then a general Raman spectrum library with 90 synthetic cannabinoids was established using KnowItAll software, which was compatible with various original spectrum formats. The analysis of 90 synthetic cannabinoid Raman spectra found that when there was no fluorescence interference, Raman spectroscopy could distinguish all synthetic cannabinoids, but showed a low discriminant ability for some structural analogues, especially those with a difference of a methyl or a halogen atom. The performance of different Raman spectrometers varied greatly, so in order to investigate the reasons for that performance differences, four handheld Raman spectrometers were selected to analyze 120 seized synthetic cannabinoid samples. Then the library search was performed using the KnowItAll software and the established general Raman spectrum library. The correct matching rates of the four Raman spectrometers were 71.7%, 68.3%, 46.7%, and 24.2%, respectively. The difference in background fluorescence reduction effect and resolution attributed to that result. The portable Raman spectrometer was simple, fast, and can be used for in-field testing. However, Raman spectroscopy can only be used for preliminary qualitative screening considering the unknown purity of the seized samples, the possible fluorescence interference, the performance of different Raman spectrometers, and the spectral library completeness. This study provided guidance for forensic science laboratories and relevant technicians to apply the Raman spectrum results correctly.
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