At lower ionization pressures, real-time explosive analysis has also been performed (~0.8-1.0 Torr). Among the explosives, only TNT and RDX showed molecular and fragment ions in the negative ion mode, as illustrated in Figures rapid peak and decrease pattern (inset in Fig. ). RDX, on the other hand, has a rapid rising EIC signal but a delayed fall with a large tailing (inset in Fig. ) . The signal of RDX's EIC tails due to its non-volatility. Because the EIC for m/z 227 (TNT) is 0.46 min and the EIC for 129 (RDX) is 0.49 min, no ion signal from RDX was recorded (Fig. ). TNT, on the other hand, gave strong molecular ion signal at m/z 227 in the RDX's EIC (Fig. ). At the reduced ion source pressure, no ion signals were recorded from NG and PETN, as previously stated . The results reveal that the fragments generated by NG and/or PETN in the glow discharge plasma may not be stable at lower ion source pressures (~0.8-1.0 Torr) or that TNT and RDX in the dc-plasma undergo electron attachment and/or capture ionization . Because of the positive electron affinity of TNT molecules, the high electron density in the HCD plasma leads to the formation of a molecular ion, ([TNT] -• , m/z 227), via an electron attachment reaction . As a result, it is reasonable to conclude that the modified HCD ion source may detect and quantify explosives from mixtures at trace and/or ultra-trace levels.