Tandem MS Elucidation\nof the Late-Stage Degradation\nMechanism of Nitroplasticizer

Understanding the degradation behavior of nitroplasticizer\n(NP)\nand the subsequent production of nitro-organics is crucial for both\nenvironmental monitoring and material development. A nontargeted approach\nvia LC-QTOF-MS was employed to thoroughly study the degradation mechanism\nof NP in its late aging stage. Both positive and negative modes of\nESI were performed to increase the compound coverage. To shed light\non the fragmentation behavior of NP degradants (e.g., compounds containing\na high density of NO<sub>2</sub> moieties and oxygen sites) in the\npositive mode, which is rarely reported, the high-resolution tandem\nMS information on precursor ions at <i>m</i>/<i>z</i> 251(+), 254(+), 266(+), and 270(+) and a pair of isomeric ions at <i>m</i>/<i>z</i> 284(+) was investigated to extract\ntheir common diagnostic ions and dissociation channels, including\nthe neutral loss of 2,2-dinitropropanol, nitro-nitrite rearrangement,\nhomolytic cleavage of NO<sub>2</sub>, and simple inductive cleavage.\nAdditionally, leveraging the sensitivity for nitroaromatics in the\nnegative polarity, negative ions <i>m</i>/<i>z</i> 182(−) and 233(−) are identified as dinitroaniline\nand dinitronaphthol, respectively, which confirm the secondary hydrolysis\npathway of the antioxidant (e.g., <i>N</i>-phenyl-2-naphthylamine)\npostulated in our previous work. In addition to earlier findings,\nthe detection of these eight degradants further supports the evidence\nof increased acid concentration and aging temperatures in the late-stage\nNP environment, which contribute to intricate degradation behaviors\nin different aging environments.