Magnum ITD

 

Magnum Ion Trap Detector (ITD) is a benchtop GC/MS product of Finnigan MAT. It operates in the GC/MS mode only, whith an upper mass limit of 650 daltons. The system is routinely operated in electron impact and chemical ionization positive ion mode. This mass spectrometer is quit different from others in a sense that ionization, mass analysis, and detection, occur in the same chamber. This feature contributes to the high sensitivity often observed with respect to quadrupole benchtop type instruments.

The ion trap assembly contains three stainless steel hyperbolic electrodes:

  • top (filament side) endcap electrode
  • bottom (electron multiplier side) endcap electrode
  • central ring electrode.

    These electrodes form a cavity in which ionization, fragmentation, storage, and mass analysis occur.

    Principle of operation


    At the GC column exit, sample molecules are introduced to the ion trap cavity, where they interact with energetic electrons (EI mode) or with preformed reagent positive ions (CI mode). Electrons are emmitted into the cavity only during a fraction of time of the scan. This fraction of time is refered to as ionization time and it's automatically controlled by the automatic scan function. This function coordinate ionization, storage, and ion ejection time for optimum sensitivities and peak shapes. After the ionization time is expired, the RF voltage applied to the central ring ramps. Ions with different masses become successively instable and are ejected to the detector. Finaly ions are collected and the signal is multiplied. The amplified ion current enter the electrometer circuit for further signal processing.