Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) applied to the analysis of explosives

Abstract

Electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) was applied to the analyses of explosives including HMTD (hexamethylenetriperoxidediamine), RDX (cyclotrimethylene trinitroamine), HMX (cyclotetramethylenetetranitroamine), PETN (pentaerythritol tetranitrate), and TNT (2,4,6-trinitrotoluene) in positive- and negative-mode of operation. A mixture of H2O/CH3OH (9/1) containing 0.01 M trifluoroacetic acid (TFA) was used as a solvent for vacuum electrospray. For all explosives described above, intact molecules were detected by EDI/SIMS. HMX which is the least volatile compound tested could be readily detected in both positive- and negative-mode of operations. Nitramines of RDX and HMX were detected as proton- and Na+-bound cluster ions with H2O and CH3OH ligands. TNT and the nitrate ester PETN were not detected in positive mode. In negative mode, RDX, HMX and PETN were detected as adduct ions with NO2−, NO3−, and CF3COO−. TNT gave TNT−• and fragment ions similar to those detected in atmospheric-pressure chemical ionization. The characteristic difference in reactivity between the nitramine compounds (RDX and HMX) and the nitrate ester compound (PETN) is likely to be due to the more diffused negative charge in nitrate ester groups than in nitro groups.