The HCD ion source was used to investigate nitroglycerine (NG), an explosive substance, in the negative mode of operation at 1, 5, and 28 Torr of ion source pressures (data is not displayed). Unlike RDX and PETN, NG did not produce any ion signal at low ion source pressures such as 1 and 5 Torr, despite increasing the amount of NG to 10 ng; nevertheless, at 28 Torr, the adduct ion for NG with NO3 -, ([NG+NO3] -, m/z 289), was seen . In the negative ion mode, NG can produce NO3 -as a fragment ion, which makes it difficult to analyze NG at low ion source pressures . This is because NO3 -is one of the HCD ion source's reagent ions (see Fig. ). As adduct ions with the NO3 -, ([NG+NO3] -, m/z 289), the thermal instability of NG causes poor detection sensitivity. also reported the formation of the ([NG+NO3] -, m/z 289) adduct ion of NG with NO3 -reagent ion . A preliminary experiment was carried out to evaluate the stability of NG by placing a significant amount on a metal substrate, and it was revealed that it decomposed above 100 °C. The ion source pressures have a significant impact on the negative mass spectra of explosive chemicals (Figs. and). In order to explore the ionization mechanism of the explosives with the ion source pressures, additional experiments for the explosives were done at a lower ion source pressure (1 Torr). By applying +0.85 kV and -0.85 kV in the positive and negative ion modes, respectively, at 1 Torr, a dc plasma was created between the transfer tube and S-lens. TATP and HMTD did not produce any ion signals in both positive and negative ion modes at 1 Torr ion source pressure, whereas RDX, PETN, and TNT produced strong ion signals in the negative mode (see Figs. ). ). Using the fabricated HCD ion source, the explosive substances did not produce any dimer ions. At 1 Torr, the LOD values of HMTD, RDX, PETN, and TNT are 20, 40, 800, and 2 pg, respectively. These explosive compounds' LOD values at 5 and 30 Torr can be found elsewhere . The DESI , DBDI , and ac-APCI all produced similar results. The HCD recorded a LOD value of 800 pg for PETN , but found only 500 fg using the DBD ion source, which is 16 times lower than the HCD ion source . This is reasonable because the DESI and DBDI generate ions in ambient conditions and introduce them directly into the mass spectrometer, avoiding thermal degradation of the compounds of interest and their ions. The generated ions in the HCD ion source, on the other hand, may be subject to thermal breakdown due to the high temperature (150 °C) of the ion source observed in this work . The HCD ion source's small size also permits the generated ions to be neutralized by hitting the ion source's walls under lower pressure. Except for TNT at 1 Torr, where TNT was observed as its molecular ion, ([TNT] -, m/z 227)