Many analytical techniques can identify explosive materials before they are detonated, and these efforts are vital in preventing terrorist acts. After an explosion, however, residues are dispersed over a large area and mixed with other particles from the surroundings, complicating identification.

Félix Zapata and Carmen García-Ruiz, University of Alcalá, Madrid, Spain, used confocal Raman microscopy to identify explosion residues. They tested their method using ten explosives that are commonly used in improvised explosive devices.

Before detonation, homogeneous organic explosives (TNT, RDX, PETN, TATP, and HMTD) all have characteristic Raman spectra. For heterogeneous inorganic/organic mixtures (black powder, dynamite, chloratite, ANFO, and ammonal), the Raman spectrum varies across the sample, and the spectra have fewer peaks.

After detonation, the Raman technique rapidly and selectively identified particles of the heterogeneous explosives as small as 10 μm in diameter. Because some particles of the combustible compounds were not in contact with the oxidizer, they survived the blast. No surviving homogeneous organic explosive particles could be detected, because the combustible species and the oxidizer are contained within a single compound.

Abbreviations

• TNT: 2,4,6-trinitrotoluene
• RDX: Research Department explosive
• PETN: pentaerythritol tetranitrate
• TATP: triacetone triperoxide
• HMTD: hexamethylene triperoxide diamine
• ANFO: ammonium nitrate/fuel oil

• Determination of Nanogram Microparticles from Explosives after Real Open-Air Explosions by Confocal Raman Microscopy,
  Félix Zapata, Carmen García-Ruiz,
  Anal. Chem. 2016.
  DOI: 10.1021/acs.analchem.6b00927