Abstract: An apparatus and method for rapidly and reliably detecting compounds of interest using mass spectra. For the apparatus, an ion mobility spectrometer is connected to an electron ionization cell which, in turn, is connected to a time-of-flight mass spectrometer. For the method, mass spectra for a compound of interest are pre-selected and then averaged over a plurality of ion, mobility spectrometer scans to create a mass spectrum which is matched against the fingerprint of the compound of interest produced by fragmenting the ions in the electron ionization cell. Additionally, a feedback mechanism is disclosed for optimizing the maximum allowable extraction frequency in the mass spectrometer.