Varian 4000 GC, Hardware Operation Manual

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Magnet Structure
03-931677-01
Magnet Disks Location
03-931761-01
Collimating Magnets
77-299014-00
External Source Assembled
After the sample is ionized, three lenses are used to direct the resulting ions
towards the ion trap using electrostatic focusing. In the case of EI, the first lens
also extracts ions from the source.
The center (L2) lens also acts to gate the ions into the trap by changing its
polarity. The lenses are nickel-plated stainless steel cylinders with an anodized
insulating layer to prevent the lens from shorting together. Each lens has a
voltage connecting post.
A heater maintains the source at an elevated temperature. Electrical connections
are made to the source through a flexible printed circuit cable that connects to
the electronics through a printed circuit board mounted to the top flange. A heat
shield between the source and the flexible cable protects the solder joints.
Hybrid Configuration
The 4000 MS supports a unique mode of operation called hybrid chemical
ionization. In the hybrid configuration, reagent ions are generated in the external
source then drawn into the ion trap to react with analytes from the GC column.
This approach has a number of potential advantages including avoiding ion
molecule reactions with the neutral reagent and avoiding losses of negative ions
that occur when they move from the external source to the trap. The hybrid mode
requires the external ionization option and a security chip to be present but does
not involve any unique hardware. In the hybrid mode, the external source must
be in place and the transfer line must be positioned with the sample directly
entering the ion trap.
Ion Trap
The ion trap assembly consists of three electrodes separated by quartz spacers,
and contained in a heated oven. The three electrodes are the entrance, ring and
exit electrodes. These electrodes have hyperbolic inner surfaces that together
form a cavity in which ionization, fragmentation, storage, and mass analysis take
place.
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