Study on Vibrational Spectral Characteristics of Fentanyl-Class Substances
XU Lin1, HE Hong-yuan1*, LIU Cui-mei2*, HUA Zhen-dong2
1. College of Investigation, People’s Public Security University of China, Beijing 100038, China
2. Key Laboratory of Drug Monitoring and Control, Drug Intelligence and Forensic Center, Ministry of Public Security, Beijing 100193, China
Abstract In this study, the infrared (IR) and Raman spectra of 28 kinds of fentanyl-class substances were analyzed. The spectrum characteristics and the distinguishing ability of IR and Raman for fentanyl-class substances were investigated. On the whole, IR and Raman spectra of fentanyl compounds showed different spectral characteristics and were complementary. For IRspectroscopy, different salt forms of fentanyl-class substances showed significant differences in the range of 3200～2 000 cm-1. The base-form compounds showed strong absorption peaks at 2 972～2 952 cm-1, the hydrochloride compounds showed multiple absorption peaks with medium intensity at 2 600～2 320 cm-1, and the citric acid compounds showed broad absorption peaks with moderate intensity at 3 100～2 800 cm-1. In addition, the IR spectra all showed a strong absorption peak caused by the stretching vibration of C═O bond at 1 750～1 630 cm-1, and a strong single or double peaks caused by the bending vibration of the benzene ring at 710～680 cm-1. For Raman, all types of fentanyl-class substances showed a strong Raman peak at 1 001～1 002 cm-1, which was caused by the in-plane bending vibration of C—H bond on the benzene ring. In the Raman spectra of substituted compounds containing alkyl, phenyl and tetrahydrofuran groups, the peak at about 1 000 cm-1 was the base peak, and the intensity of other peaks was all lower than 30% of the base peak. For Raman spectra of substituted compounds containing fluorine, furan and sulphur groups, there were other high-intensity peaks besides the base peak at about 1 000 cm-1. IR spectrum can distinguish all fentanyl-class substances, even for certain structural analogues with high spectrum similarity. When there is no fluorescence interference, Raman spectra are distinguishable for all fentanyl-class substances. The Raman spectra for homologues with differences in only a methyl group and regioisomers with methyl substituted at different positions were found to be highly similar; however, their spectra demonstrated small but detectable differences. Both the Infrared and Raman methods were simpler, more rapid, less expensive, non-destructive, and fit for in-field testing. Raman may be used non-invasively, minimizing exposure to potentially dangerous substances; however, its fluorescence based problem sometimes affects its usefulness. Compared with Raman, IR shows no fluorescence interference, higher spectrum consistency, and a more complete commercial spectrum library, which is the preferred method for rapid qualitative analysis of fentanyl-class substances in-field.
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