In conclusion, the developed HCD ion source had better sensitivity for analyzing explosives such as HMTD, TATP, RDX, PETN etc in both positive and negative ion modes under high ion source pressures, e.g., 5 and 28 Torr, but the low ion source pressure HCD (1 Torr) gave ultra-trace level detection for TNT (LOD 2 pg) in the negative ion mode . Through ionmolecule reactions, no cluster ions were seen from RDX and PETN at 1 Torr, however these two explosives generated fragment ions with improved sensitivity, especially RDX at lower ion source pressures (1 Torr). Under low ion source pressure (e.g., 1 Torr) in the HCD plasma, electron density reaches maximum levels, allowing compounds with positive electron affinity to participate in electron attachment processes. Accordingly, electron attachment processes revealed TNT's molecular ion, ([TNT] -, m/z 227), as the main ion, whereas electron capture dissociation in the negative ion mode revealed RDX and PETN at 1 Torr . Electron affinity of TNT was calculated to be between 0.6 and 0.7 eV . At low ion source pressure, the electron capture dissociation processes of RDX and PETN yielded their fragment ions as the major ions (1 Torr). At higher ion source pressures such as 5 and 28 Torr, RDX and PETN generated cluster ions with the reagent ions, namely NO2 -, NO3 -, whereas AN produced cluster ions of HNO3 with NO3 -, ([HNO3+NO3] -, m/z 125) . This is because in plasma-excited air, AN decomposes to HNO3, and the resulting HNO3 forms a cluster ion with the majority NO3 -ion in the HCD ion source. TNT had the most pressure-dependent mass spectra of all the explosive chemicals. The predominant ion signal for TNT at 1 Torr was its molecular ion,