Methods and apparatus for monitoring air samples for the presence of the explosive TATP are disclosed. A preferred approach employs proton transfer reaction mass spectrometry PTR-MS). The system may be operated continuously on a real time or near real time basis. A delivery tube of specific dimensions and materials is employed to introduce the sample into the ionization chamber which in turn generates the ions which are delivered to the mass spectrometer for determining the m/z values. The system may employ a plurality of ionization chambers to reduce the amount of false negative identifiers. A multiple inlet ion funnel may be employed to combine the ions from each of the ionization chambers. Chemical ionization may be employed. A validation module may be employed to reduce the amount of false positive identifiers.