Analyzer 7
5977B Series MSD Troubleshooting and Maintenance Manual 185
EI Ion Source
The EI ion source (See Figure 40 on page 186) operates by electron ionization.
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.
Ion source body
The ion source body (See Figure 40 on page 186 and Figure 41 on page 187) is
a cylinder. It holds the other parts of the ion source, including the lens stack.
With the repeller, and in the SST/Inert ion source, the drawout plate, it forms
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 unionized sample molecules or fragments.
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