Development of Mass Spectrometric Method for Analysis of Cyclic Nitramine Explosives DTIW and HNIW

Mass spectrometric (MS) methods are used for the analysis of two novel nitramine explosiveshexanitrohexaazaisowurzitane (HNIW) and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurzitane (DTIW). The methods include electrospray (ESI) and atmospheric pressure chemical ionization techniques for liquid chromatography/MS (LC/MS), chemical ionization for direct introduction (DCI), and gas chromatography/MS (CI-GC/MS). It is found that HNIW (438 Da) is detectable using both positive and negative modes of DCI and in the negative mode ESI-MS. Several anions were found to complex with HNIW, e.g., CF₃CO₂^-, Cl^-, Br^-, I^-, NO₃^-, and NO₂^-. On the other hand, DTIW could only be detected using positive DCI and CI-GC/MS, where an MH⁺ ion (m/z 263) was formed. The fragmentation pathways of the two nitramines were further studied by MS² experiments. Apparently, the main fragmentation pathway of the MH⁺ ion of DTIW involves the loss of nitrous acid. Several anion adducts of HNIW that were studied dissociate to afford neutral HNIW and the added anions. However, Cl^-, Br^-, I^-, and NO₂^- afford a series of fragments that resulted from the dissociation of the isowurzitane structure. For these anions, limit of detection was also found. To understand some of the HNIW fragmentation pathways, DFT calculations were used.