Characterization of cyclotetramethylenetetranitramine (HMX) thermal degradation by isotope analyses with analytical pyrolysis-atmospheric pressure ionization tandem mass spectrometry

Analytical pyrolysis‐atmospberic pressure ionization (Py‐API) tandem mass Spectrometry was used in the structure elucidation of the oxidalive and non‐oxidative thermal decomposition products of cyclotetramethylenetetranitramine (HMX). The [15NO2]‐, [15N8]‐ and [2H8]‐HMX isotope preparations provided fundamental information in the determination of the identities of the various pyrolyzate species. All RDX pyrolysis product ions that were identified by Py‐API tandem mass Spectrometry, i.e. m/z 44, 60, 74, 75, 85 and 98, were present in the pyrolyzate of HMX. In both RDX and HMX investigations, these ions provided identical mass spectral daughter ion analyses. HMX, however, provided additional ions at m/z 30, 58, 69, 71, 83 and 141. Of all thirteen ions identified in the Py‐APJ mass spectrum of HMX, only that at m/z 75 contained a nitrogen atom that originated from the NO2 group. Standards analysis confirmed the identities of the ions at m/z 69, 71 and 141 as methyleneaminoacetonitrile, methylaminoacetonitrile and the caged compound hoxamethylenetetraamine, respectively. Isotopic analyses provided a high degree of confidence on the structural assignments of the ions at m/z 30 and 58 as methyleneimine and methyleneformamide; the ion at m/z 83, however, appeared to be a heterocyclic compound with daughter ion mass spectral elements similar to but not identical with that of 1‐methylimidazole and 3‐methylpyrazole.