At lower ion source pressures (0.8-1.0 Torr), TNT showed a better LOD value (1.00±0.03 pg). The electron attachment reaction of TNT molecules (EA: 2.5 eV) is facilitated by the glow discharge-like plasma at lower ion source pressures, resulting in the formation of the molecular ion ([TNT] -, m/z 227) . Because of the low pressure, only a little amount of NOx was formed, hence TNT molecules were mostly involved in the electron attachment reaction, despite the electron affinity of NO3 being 3.92 eV . For RDX, the m/z 129, [M-NO2-HNO2] -, a fragment ion of RDX, had a better LOD value (10.33±0.45 pg), but the ([RDX+NO3] -, m/z 284) had a greater LOD value (30.75±0.95 pg) . Using a glow discharge ion source operating at 0.80 Torr of air pressure, found improved sensitivity for RDX with a few pg .