The hollow cathode effect has been exploited in the manufacture of hollow cathode lamps for AAS/AES since Friedrich Paschen discovered it in 1916. Lindinger and colleagues used the HCD as an ion source in proton transfer reaction mass spectrometry for the first time. The purpose of this review is to conduct a literature review on the fabrication of a variable-pressure HCD ion source for MS in detection, quantification and investigation of gas phase ionmolecule reactions of explosives and related compounds. The use of air as a carrier gas in the HCD ion source eliminates the need to change reagent gases like He or Ar on a regular basis, making the ion source more practical for MS applications. The HCD ion source has been designed in such a way that it can accurately and simultaneously detect explosives and related substances at trace to ultra-trace levels. The HCD performs well at high ion source pressures (28.0-30.0 Torr), whereas the conventional GD appears at low ion source pressures (0.8-1.0 Torr). At 28-30 Torr, the explosive and related compounds produced ions in both positive and negative modes; however, at 1 Torr, electron attachment/electron capture processes produced exclusively negative ions. In the positive ion mode, HMTD and TATP produced ions exclusively at higher ion source pressures (5.0-30.0 Torr), but the ion intensities rose when the ion source pressure was increased from 5.0 to 30.0 Torr. As a result, the fabricated variablepressure HCD ion source can be used in combination with an ion trap mass spectrometer that uses air as a carrier gas to detect and quantify explosives and related compounds at trace-toultra-trace quantities in the real world.