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Ion Source
The ion source operates by electron ionization (EI) or chemical ionization (CI). The sample
enters the ion source from the GC/MSD interface. Electrons emitted by a filament enter
the ionization chamber, guided by a magnetic field. The high-energy electrons interact
with the sample molecules, ionizing and fragmenting them. The positive voltage on the
repeller pushes the positive ions into the lens stack, where they pass through several
electrostatic lenses. These lenses concentrate the ions into a tight beam, which is directed
into the mass filter.
Common Measures of Instrument Performance
• Abundance of certain ions (e.g., percentage of the 502 ion from the Autotune report).
• Shape of lens ramps and the chosen voltages, especially Repeller Ramp.
• Sensitivity obtainable for a given analysis.
• Ability to tune to a given reference compound (e.g., DFTPP).
Maintaining the Ion Source
Cleaning procedures for MSDs vary. Refer to your Troubleshooting and Maintenance
manual for specific ion source cleaning procedures.
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