NO3− loss from nitrate adducts of explosives by thermal decomposition in tandem Ion mobility spectrometry and by collision induced dissociation in tandem mass spectrometry

Nitrate adducts of nitroglycerin (NG) and 1,3-dinitroglycerin (1,3-DNG) were produced from atmospheric pressure chemical ionization with chloride reagent ions and in-source decomposition of M·Cl⁻. The nitrate adducts subsequently dissociated in the drift region with enthalpies of 109 ± 9 kJ mol ⁻¹ at 142–150 °C for NG·NO₃⁻ and 101 ± 8 kJ mol⁻¹ at 161–173 °C for 1,3-DNG·NO₃⁻. Similar behavior was not observed generally for other explosives although nitrate adducts of each explosive could be formed using electrospray ionization with a nitrate salt solution. Ion abundances were measured over a range of ion energies with collision induced dissociation in tandem mass spectrometry and models from Density Functional Theory were used to correlate the experimental findings to structural motifs and other adduct properties. The computational modeling showed that adduct stability is dominated by the electrostatic interaction between the nitrate ion and the dipole moment of the neutral explosive. Specifically, explosives having the ability to adapt a conformer with a large dipole moment showed the most stable adducts. Other binding contributions are possible yet were found to be minor in the explosive adducts studied here.