The HCD ion source was designed for the purpose of analyzing explosive compounds . TATP and HMTD mass spectra were measured in the positive mode, and RDX, PETN, TNT, NG, TNB, DNT isomers, 2A-DNT, and 4A-DNT mass spectra were measured in the negative mode by setting the ion source pressures to 1, 5 and 28 Torr. The temperatures of ion sources used in explosives analysis can be found elsewhere . Wiley and Frontiers Media S.A. have granted permission for this reprint . Scheme 1. The HCDI-MS system's versatility in analyzing explosives in both negative and positive modes of operation. ) came from oxygen molecular ions, (O2 + , m/z 32), and protonated acetone, [(CH3)2CO+H] + , m/z 59); whereas, the major ions in the negative ion mode were (NO2 -, m/z 46), (CO3 -, m/z 60), and (NO3 -, m/z 62). Protonated acetone, [(CH3)2CO+H] + , m/z 59), is a reasonable base peak in the positive ion mode. This is due to the presence of organic solvents such as acetone, ethanol, methanol, ammonia etc in laboratory air. In the positive ion mode, the formation of the protonated acetone, [(CH3)2CO+H] + , ion functions as the primary regent ion for the protonation of TATP and HMTD. The HCD plasma energized the ambient air molecules, resulting in the creation of NO2 -, CO3 -, and NO3 -ions, and they appeared in the negative ion mode, as shown in Fig. . (b). The mechanism of generation of NO2 -, CO3 -, and NO3 -ions in plasma-excited air was also explained by Sekimoto and Takayama (2010) .