Analytical Techniques for Forensic Investigation of Oversized and Fragmented Exhibits in Mixed Explosive Detonations

Background/Objectives: Post-blast forensic investigations frequently involve oversized exhibits, such as vehicle fragments, concrete blocks, and metallic debris, which are often contaminated with mixed explosive formulations. These heterogeneous substrates present significant challenges for residue recovery and analysis when conventional methods, optimized for small, homogeneous samples are applied. This study aimed to develop and evaluate forensic strategies tailored to oversized and fragmented evidence from mixed explosive detonations. Methods: Oversized exhibits from ANFO–nitrate detonations were examined using sequential swabbing, solvent extraction, and spatial subsampling techniques. Organic residues were characterized using Thin Layer Chromatography (TLC) and Gas Chromatography–Mass Spectrometry (GC–MS), while inorganic ions were identified through chemical spot tests and Fourier Transform Infrared (FTIR) spectroscopy. The efficacy of syringe filtration was further assessed to improve the residue recovery efficiency. Results: GC–MS analysis of ether extracts confirmed the presence of high-boiling petroleum hydrocarbons, consistent with diesel fractions in ANFO. Inorganic analyses revealed the presence of ammonium and potassium nitrate, whereas chlorate, perchlorate, and metallic additives were absent. Spatial subsampling enhanced the detection sensitivity, and syringe filtration produced the highest recovery yield by minimizing background interference. Conclusions: The integrated workflow, which combines targeted swabbing, sequential solvent extraction, syringe filtration, and complementary analytical methods—proved highly effective for investigating oversized post-blast exhibits. This approach improves residue recovery, enhances analytical reliability, and strengthens evidentiary interpretation, providing a robust framework for the forensic investigation of complex detonation events in the future.