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Some FID's with very high purity gases and low
bleed columns will have a background under 2 pA
when they are actually lit. If this is the case, the
Lit Offset value can be lowered in the detector
configuration. If the Lit Offset is set too low, the
flame may never try to re-ignite. If the flame is
lit, a cold glass should show condensation if held
above the FID.
To determine if Lit Offset is the cause of the
problem, set it to [0] and confirm that the flame
stays lit for an entire run. If it does, choose a
lower setting for Lit Offset that is appropriate
for the specific FID background of that GC.
Also, the FID temperature should be maintained
at least 20°C > the final oven temp of the GC
analysis. The FID should never be operated at
less than 300°C. This temperature will not
damage columns with a maximum temperature
lower than 300°C.
Released: April 2004
Procedure
The following procedure will help determine the
root cause(s) for difficulty lighting the FID.
1. Insure the proper jet is installed.
2. Confirm the integrity of the gas supply.
6850 Series Gas Chromatograph Service Procedures
Check gas purities. Leak test the plumbing
modules.
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