The negative mass spectra of NG, TNT, PETN and RDX at the higher ion source pressure are shown in Figures show the mass spectra of the explosive compounds at the lower ion source pressures. The spectral pattern for the explosives examined separately for both higher and lower ion source pressures is identical with a little change with that recorded concurrently, as shown in Figure . The spectral pattern for 1 ng RDX examined separately revealed adduct ions with both NO3 - and NO2 -ions, ([RDX+NO3] -, m/z 284) and ([RDX+NO2] -, m/z 268) (Fig. ), whereas the simultaneous measurement for 1 ng RDX revealed only the ([RDX+NO3] -, m/z 284) ion signal (Fig. ). Both the NO3 -and NO2 -ions have a trigonal planar shape, with the oxygen atoms of each ion being extremely negatively charged. RDX has three nitro groups (NO2), each of which has a very positive charge on its nitrogen atoms . With RDX and its homologue, These findings revealed that under the hard HCD plasma environment at the higher ion source pressure, the majority of the ions that occurred at lower m/z values originated from the m/z 242.