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

RATIONALE: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.