Separation and characterization of the impurities in 3,3-diamino-4,4-azoxyfurazan by ultrahigh-performance liquid chromatography combined with Q‑orbitrap mass spectrometry

Abstract

Recently, 3,3-diamino-4,4-azoxyfurazan (DAAF) as one of most promising energetic furazan compounds has been widely studied because of its excellent explosive performances. Nowadays, the Oxone oxidation method is regarded as a main pathway to synthesize DAAF. However, several unknown impurities are yielded when the Oxone method is used to prepare DAAF. The identification of DAAF’s impurities is beneficial to optimize synthetic route of DAAF and then improve its purity. In this study, chemical structures of DAAF and its main impurities were analyzed by developing an unknown analysis workflow based on ultrahigh-performance liquid chromatography-tandem diode array detector -tandem high resolution mass spectrometry (UHPLC-DAD-HRMS). They were fully separated by UHPLC after the optimization of chromatographic conditions. HRMS based on a Q-Orbitrap system was performed to elucidate chemical structure of the impurities by determining exact mass of the impurities and their MS/MS fragments. Besides DAAF, eight unknown impurities were detected under negative ion mode ([M-H]-) of HRMS with a heated electrospray ionization. Comprehensive analysis of UHPLC-DAD-HRMS provided more information including the retention time, UV–Vis spectrum, elementary composition and MS/MS fragments, and then possible structures of the impurities were proposed in this work. Further, the ion at m/z 211.0328, impurity I and impurity V were confirmed to be DAAF, DAF and DAAzF, respectively, through 1H NMR and 13C NMR after synthesizing their reference materials. In addition, the source of these impurities during the synthesis of DAAF has been analyzed. The impurities were originated from the precursor, the intermediate and byproduct of preparing DAAF through the hydrazine, the isomerism and the nitrosation.