Low-frequency Raman spectrum of methamphetamine hydrochloride and its alterations induced by impurities

Methamphetamine is one of the most abused drugs worldwide. Forensic laboratories have developed various methods to analyze methamphetamine for identifying and comparing seizures. These methods basically focus on the physicochemical properties of the methamphetamine molecule. Because methamphetamine is commonly distributed in its hydrochloride salt form, information on the crystalline state of methamphetamine could give new insight for forensic drug analysis. To grasp this information, we applied low-frequency Raman spectroscopy to methamphetamine hydrochloride. A laboratory-built low-frequency Raman microspectrometer was used for measuring low-frequency Raman spectra of optically pure and racemic methamphetamine hydrochloride. A mixture of methamphetamine hydrochloride with dimethyl sulfone, which is frequently added as a diluent to illicit methamphetamines, was also measured. An ab initio calculation was performed to assign peaks in the low-frequency spectra. The phonon modes of methamphetamine hydrochloride, and their changes induced by impurities are discussed. To the best of our knowledge, this is the first reported application of low-frequency Raman spectroscopy technique to methamphetamine hydrochloride.