In MS, the analyte molecules must be desorbed into the gas phase and then ionized using a suitable ion source for detection and quantification. The volatility of condensed substances affects their desorption. Because different explosive compounds have varying vapor pressures, their desorption processes are likewise variable. On the basis of their EICs, we investigated the desorption process of various explosives from their mixture (EICs). On a glass slide, 2 μL of acetonitrile solution containing 1 ng of each explosive compound was poured and air dried. To 378) appeared as a minor ion. For the ([PETN+NO3] -, m/z 378) ion, the concordance between the fast increase and fall and the very low intensity is reasonable. There could be two reasons for this. To begin with, PETN molecules may be thermally labile, hence the majority of PETN molecules were fragmented prior to ionization. Second, the PETN molecules' ion production efficiency with the NO3 -ion is not as good as RDX's with the NO3 -. In the mass spectrum, a fraction of the PETN molecules formed adduct ions with the NO3 -(Fig. ). The PETN adduct ion ([PETN+NO3] -, m/z 378) was detected using the EICs for ([TNT+NO3-HNO2] -, m/z 242) (Fig. ) and [RDX+NO3] -, m/z 284) (Fig. ). The fact that the ([PETN+NO3] -, m/z 378) appears in the RDX spectrum with a relatively low intensity further shows that it is non-volatile (Fig. ). The modified HCD ion source is capable of detecting many explosives at trace levels. As a result, the improved HCD ion source has been found to be capable of concurrently detecting explosives of several types at trace levels.