Characterization of vapor emissions from pentaerythritol tetranitrate solids in nitrogen by atmospheric pressure chemical ionization mass spectrometry and in ambient air by ion mobility spectrometry

The emission of vapors from solid samples of Pentaerythritol Tetranitrate (PETN) in a flow of nitrogen from ~20 to 140°C was characterized using atmospheric pressure chemical ionization mass spectrometry equipped with a 63Ni ion source. Mass analysis of ions derived from vapors from military grade PETN at room temperature, without deposition from solution, included only NO3− (62 Da) and HNO3·NO3− (125 Da) and were attributed to residual levels of nitric acid in the PETN solid. The vapor level of HNO3 persisted until 80°C and after this declined asymptotically to background levels; ions observed above 110°C were nitrate adducts of molecular PETN including (PETN)n·NO3− with mass values of 378 Da (n = 1) and 695 Da (n = 2). Subsequent reheating of the PETN solid caused an increase release of nitric acid and formation, above 140°C, of the same nitrate adducts of PETN,, consistent with thermal degradation of some PETN to nitric acid. A commercial handheld ion mobility spectrometer was used to sample airborne vapors from solid PETN in an open container and heated in ambient air. The ion mobility spectra showed that ionization chemistry was rapidly transformed from O2− to NO3− which persisted indefinitely and produced ion above 80°C with Ko values of 1.48, 1.21, 1.15, and 1.10 cm2/V s. These relatively low-mobility peaks were attributed to cluster ions of nitrate with nitric acid and molecular PETN generated from thermal decomposition and some vaporization of solid PETN. Persistence of nitrate as a reactant ion in the handheld analyzer suggested a need for specialized designs and materials for such explosives vapor measurements.