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Forensic science international

Analysis of chemical warfare agents by portable Raman spectrometer with both 785nm and 1064nm excitation.


PMID 30125768

Abstract

The Raman spectra of twenty-two chemical warfare agents (CWAs) were measured: eleven nerve agents and their precursor, five blister agents, three lachrymators, one choking agent, and one vomit agent, in liquid or solid state in colorless transparent vials were analyzed using a portable Raman spectrometer, Xantus-2 from Rigaku Corporation, equipped with selectable excitation lasers (785nm and 1064nm). With 785nm excitation, characteristic Raman spectra composed of many sharp peaks were observed for twenty CWAs, but nitrogen mustard 3 (HN3) and adamsite (DM) did not show particular peaks owing to broad and intense mountain-like baselines. With 1064nm excitation, Raman spectra similar to those with 785nm excitation were observed for the twenty CWAs, where the wavenumbers of the peak tops and comparative heights were similar to those with 785nm excitation. Characteristic Raman spectra with several sharp peaks could be even obtained for HN3 and DM with 1064nm excitation. The resolutions of the peaks in the spectral region below 1000cm-1 were higher with 785nm excitation than those with 1064nm excitation. In contrast, those above 1000cm-1 were almost compatible with both excitations. The heights of the peaks in the spectral region lower than 1000cm-1 were significantly higher with 785nm excitation than those with 1064nm excitation, but those higher than 1000cm-1 were almost compatible with both excitations. The CWAs could be discriminated based on the Raman spectra showing respective unique fingerprint patterns, even among six alkyl methylphosphonofluoridate congeners. Structural assignment to Raman bands observed in the spectra was also proposed. The influence of mixing with gasoline to match the quality of library search was examined for seven representative CWAs. With 785nm excitation, the hit quality index (HQI) of sarin was higher than 50% when the concentration (V/V) was higher than 25%. Meanwhile, with 1064nm excitation, HQI of sarin was higher than 50% even when the concentration was as low as 15%. With 785nm excitation, the HQI of L1 was higher than 50% when the concentration was higher than 80%. However, with 1064nm excitation, the HQI of L1 was higher than 50% when the concentration was 20%. Measurements with 1064nm excitation seemed superior in identifying CWAs in a gasoline mixture using the library search. The Raman spectra with 785nm and 1064nm excitation were compared in the measurement in the amber glass containers.