Secondary ion mass spectrometry of powdered explosive compounds for forensic evidence analysis

Residual quantities of explosives deposited on, or absorbed in, nearby surfaces can be of forensic value in post-blast analysis. As secondary ion mass spectrometry (SIMS) may be a suitable analytical approach for the screening of such residues, its performance was evaluated.

The analyses were carried out in a SIMS instrument fitted with a quadrupole analyzer. The sample was sputtered at a 45º incidence angle with a 100 µm primary Ar(+) beam (3 keV, 500 nA). Surface sample compensation was performed with low-energy electrons (500 eV, 0.75 mA).

TNT, RDX, PETN and cloratite were deposited in powdered form on double-sided tape and introduced into the mass spectrometer, without further handling, for SIMS analysis. The analysis conditions including compensation were optimized. A mixture of energetic compounds commonly used for explosive preparation was also analyzed, proving the potential of SIMS in forensic analysis.

This study demonstrated the possibility of detecting explosives by SIMS making use of a simple sampling procedure consisting of sticking the sample in powdered form (compatible with the collection performed in forensic post-blast analysis) onto double-sided tape without handling or preparation.