Characterization of RDX and HMX explosive adduct ions using ESI FT-ICR MS

Investigation of two common explosives such as cyclonite (RDX) and cyclotetramethylenetetranitramine (HMX) using a mass spectrometer with ultrahigh resolution and accuracy has not been comprehensively performed. Here, ultrahigh mass accuracy 15-T Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) spectra were utilized to comprehensively characterize the adduct ions of RDX and HMX. Two different ionization sources such as a conventional electrospray ionization (ESI) source and a chip-based static nano-ESI source were used to investigate the adduct ions of RDX and HMX. The ESI-MS analyses of two explosives in negative ion mode provide some adduct ions of RDX and HMX even without prior addition of their corresponding anions. A total of six types of adduct ion were characterized: [M + Cl]^- , [M + HCOO]^- , [M + NO₂ ]^- , [M + CH₃ COO]^- , [M + NO₃ ]^- , and [M + C₃ H₅ O₃ ]^- , where M is either RDX or HMX. The ultrahigh accuracy of the 15-T FT-ICR MS was utilized to distinguish two closely spaced peaks representing the monoisotopic [M + NO₂ ]^- and second isotopic [M + HCOO]^- ions, thereby enabling the discovery of a [M + NO₂ ]^- adduct ion in the ESI analysis of RDX or HMX. [M + NO₂ ]^- and [M + CH₃ COO]^- adduct ions were only observed when using a static nano-ESI source. It is the first report explaining the discovery of [M + NO₂ ]^- adduct ion in the ESI-MS analyses of RDX and HMX.