Agilent Technologies 6850 Series II User Information page 189

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Warning Wear safety glasses for the next procedure. FID exhaust can be harmful.
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Thermal cleaning (bakeout)
Elevated background signals (>20 display units with the flame on) may be due
to contamination in the detector. If so, this bakeout procedure may reduce the
background level.
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Released: March 2004
Check that the right type of jet is installed for the column you are using.
Check that the jet is not damaged. Look for scores, galls, a crimped tube,
or a plugged jet.
Injecting large volumes of aromatic solvent can cause the flame to go out.
Switch to a nonaromatic solvent.
The lit offset value may be too low or too high. Adjust the value.
Check the ignitor by turning the flame off, then on again. If the ignitor is
working properly, you will be able to see a glow from the detector
chimney.
Turn the detector off, remove the column from the GC, and cap the
detector fitting.
Cap the inlet fitting.
Reset the detector temperature to 375°C.
Reset the oven temperature to 250°C.
Ignite the flame and monitor the detector signal; it should rise quickly to
some higher value as the FID heats up, then decrease to some reasonably
constant value.
Reinstall the column in the GC.
Restore the original setpoint temperatures and allow the unit at least
2 hours to stabilize. Observe the detector signal to determine if it is now
within the acceptable range.
If repeated bakeouts do not give an acceptable signal level, the gases may
be impure. Higher purity gases and/or traps may be necessary. If cleaning
the gases fails to give an acceptable signal level, a thorough mechanical
cleaning, as described in the following pages, may be necessary.
6850 Series II GC User Information
Routine Maintenance: Detectors
Maintaining a flame ionization detector (FID)
page 189 of 256