Among the explosive compounds, TNT ionization is strongly dependent on the ion source pressure (see Figs. ), (c1), and 5(c)). Additional experiments were carried out using air and nitrogen as carrier gases to examine the ion generation mechanism of TNT molecules with ion source pressure. Figure (a) illustrates a schematic of the manufactured HCD ion source, which has two inlets: inlet-1 was used to introduce the analytes into the ion chamber with air while inlet-2 was closed (see Fig. ). A sample was introduced through inlet-2 while inlet-1 was closed to confirm the ionization of TNT with varying ion source pressures, as illustrated in Fig. NO] -, m/z 197), however it had a low intensity. The ionization mechanism of TNT was investigated using ambient ion sources such as DBDI , dc-corona APCI , electrospray-based methods , and ac-corona APCI . TNT produced its are determined by the presence or absence of air in the plasma/glow. As a result, it can be stated that analyzing explosives at the trace-level is a challenging task from an analytical standpoint.