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A molecule ion reactor (MIR), i.e. a gas filled radio-frequency only quadrupole with a longitudinal electrical field (RFQLEF), is used as an atmospheric pressure ionization interface for an orthogonal time-of-flight mass spectrometer (O-TOFMS). A new phenomenon of selective ion 'heating' in a MIR near Mathieu's instability threshold was found and confirmed by computer simulation. The 'heating' in collisions with buffer gas molecules leads to ion decomposition. In the case of multicharged ions, fragments with an m/z value higher than that of the parent ion have a stable motion and can be analysed by an O-TOFMS. Fragmentation of bradykinin and beta-endorphin molecular ions having a selected charge state is demonstrated. The spectra show clear 'ladder' structure. The phenomenon may be used as an alternative to tandem mass spectrometry (MS/MS) for molecule structure analysis.

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A concept of an "ideal" orthogonal-injection time-of-flight (O-TOF) mass spectrometer is proposed and a new high-resolution O-TOF mass spectrometer with an electrospray ion source and a molecule-ion reactor is described. The instrument design was optimized for high resolution and sensitivity using the concept of an ideal O-TOF mass spectrometer. A mass resolving power of about 20,000 (full width at half maximum) and a mass measurement accuracy in the 10 ppm range is demonstrated.

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