192 5977B Series MSD Troubleshooting and Maintenance Manual
7 Analyzer
HES EI Ion Source
The HES EI ion source operates by electron impact ionization. The sample
enters the ion source from the GC/MS 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, directed into the mass filter.
Ion source body
The ion source body is a cylinder. It holds the other parts of the ion source,
including the lens stack. The repeller, source mount, and filament block form
the ionization chamber. The ionization chamber is the space where the ions
are formed. Slots in the source body help the vacuum system to pump away
carrier gas and un-ionized sample molecules or fragments.
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