Assessment of handheld Raman spectroscopy for forensic analysis of dark-colored bulk explosive fuel–oxidizer mixtures

Abstract

The field identification of explosives is critical for crime response, requiring specialized protocols and often the support of Explosive Ordnance Disposal (EOD) teams to ensure safety. Handheld Raman spectrometers are widely used for this purpose due to their portability, nondestructive analysis, and ability to detect both organic and inorganic compounds with minimal sample preparation. However, their effectiveness is limited for dark-colored explosives—such as black powder, flash powder, and sulfur-chlorate explosives—commonly encountered in criminal activities. These mixtures pose unique challenges, including poor spectral quality caused by light absorption and the risk of ignition during direct analysis. This study addresses these challenges by introducing a simple and effective methodology for the safe identification of oxidizing salts in dark-colored fuel–oxidizer mixtures using handheld Raman spectrometers. The approach involves aqueous extraction followed by Raman analysis of the extract, improving safety and yielding reliable results by circumventing the limitations of direct solid analysis. Results confirmed that direct analysis of these mixtures is unsafe and ineffective, with three mixtures igniting during testing and others providing insufficient spectral data. In contrast, the aqueous extraction method enabled the successful identification of oxidizing salts in all tested samples using basic materials commonly found in crime scene kits. This technique supports field investigations, such as the seizure of suspected explosive materials, helping in decision-making during on-site investigations.