Fast Atom Bombardment and Electrospray Tandem Mass Spectrometry. Some Fragmentation Reactions in Cyclic Nitramines Studied Using Collision-Induced Dissociation

The initial fragmentation pathways of some cyclic nitramines containing nitroguanidine and/or secondary nitramine groups were identified by fast atom bombardment (FAB) ionization mass spectrometry. Their partially nitrated analogues were analyzed as nitric acid salts using both FAB and electrospray (ES) ionization mass spectrometry. The ES technique gave simple mass spectra dominated by the more diagnostic higher molecular-mass species, which were ideal for tandem mass spectrometry (MS/MS) studies. Fragment-molecule adduct ions of the type [MH + NO₂]⁺ and/or [MH + NO]⁺ were observed in the FAB spectra in some cases. Fragmentation processes of these and the protonated molecules, together with some fragment ions, were elucidated. The main fragmentation processes were the loss of H₂O, NO₂ group(s) and to a lesser extent NO. Minor transitions involving ring fragmentations were more favorable for the nitric acid salts than their more highly nitrated analogues.