Systematic analysis of post-blast organic traces in soil, application of color tests, TLC, GC–MS, and ITMS

Abstract

The post-blast trace analysis of explosives is inherently complex, requiring the separation and identification of multiple unknown compounds within contaminated matrices. The study explores modified methods for the extraction, analysis, and detection of post-explosion residues, of the three main organic explosives groups, focusing on key explosives such as NC (Nitrocellulose), NG (Nitroglycerin), Tetryl, TNT, RDX, PETN, as well as sheet and plastic explosives. A comprehensive protocol was developed, involving sample extraction, filtration, and clean-up processes, followed by analysis using a range of analytical techniques. The study introduces an optimized spot test scheme and proposes novel TLC mobile phases for improved separation and characterization of explosives. In addition, a new GC/EI-MS method was developed for the selective detection of PETN, overcoming common thermal degradation issues.

The presented GC–MS findings of this study demonstrate the significant advancements made in overcoming these obstacles, providing a clearer understanding of the analytical improvements enabling its reliable detection. Ion Trap Mobility Spectrometry (ITMS) was employed for evaluating the concentration-time decay of explosive residues on hand swabs, revealing that NG exhibited higher persistence than TNT. The study determined the Minimum Detection Limits (MDL) to be 2 ng for TNT, 3 ng for RDX and NG, and 4 ng for PETN. The research underscores that the effectiveness of explosive detection methods depends on aligning techniques with the physical and chemical properties of the analytes. Results also emphasize the importance of using confirmatory techniques beyond TLC and spot tests, as these methods are presumptive analyses and insufficient for independent compound identification. The proposed TLC mobile phases achieved significant resolution of the studied explosives, achieving significantly improved R_f values for a wide range of explosives across different groups, confirming their suitability for forensic applications. This study establishes that GC/EI-MS with its basic set, can be used for PETN analysis, while ITMS offers a fast and reliable approach for field detection and persistence studies. Collectively, these findings contribute to the analytical protocols for forensic explosive residue analysis.