New qualitative analysis strategy for illicit drugs using Raman spectroscopy and characteristic peaks method

Area of Science:

• Forensic Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Fast qualitative identification of seized illegal drugs using Raman spectroscopy is hindered by fluorescence and sample complexity.
• Existing methods struggle with accurate identification in the presence of cutting agents and interfering fluorescence.
• Optimizing excitation wavelengths and developing new analytical strategies are crucial for enhancing drug analysis.

Purpose of the Study:

• To compare the effectiveness of 785-nm, 1,064-nm, and sequentially shifted excitation (SSE) for reducing fluorescence in drug identification.
• To evaluate the characteristic peaks method as a novel strategy for overcoming fluorescence and cutting agent interference.
• To assess the sensitivity and accuracy of Raman spectroscopy combined with the characteristic peaks method for analyzing diverse seized drug samples.

Main Methods:

• Comparison of three excitation sources (785-nm, 1,064-nm, SSE) for Raman spectroscopy.
• Application of the characteristic peaks method, independent of cutting agents, for qualitative analysis.
• Analysis of a large dataset of seized illegal drugs: methamphetamine, ketamine, heroin, and cocaine samples.

Main Results:

• Methamphetamine, ketamine, and cocaine samples exhibited minimal fluorescence, showing limited benefit from 1,064-nm or SSE excitation.
• Heroin samples showed significantly improved detection rates with 1,064-nm (60.8%) and SSE (61.4%) compared to 785-nm (13.1%), though fluorescence was not fully eliminated.
• The characteristic peaks method achieved low limits of detection (5%-20%) for drug mixtures, outperforming library searching for 60% of samples.

Conclusions:

• Raman spectroscopy, particularly with 1,064-nm excitation and SSE, offers enhanced detection for fluorescent samples like heroin.
• The characteristic peaks method significantly improves the accuracy and sensitivity of qualitative drug analysis, even with complex mixtures.
• The combined approach of Raman spectroscopy and the characteristic peaks method provides a fast, simple, and accurate solution for seized drug identification.