Troubleshooting
6850
6850
Released: April 2004 6850 Series Gas Chromatograph Service Procedures 295
Detectors
Flame ionization detector
Baseline problems
The purpose of this section is to outline a logical
procedure for troubleshooting FID baseline prob-
lems, including noise, high background, drift, or
cycling.
The 6850 FID uses a hydrogen flame to burn
organic samples, resulting in increased ionization
that is measured as a current in the
5 to 10^6 pA range. Normal FID background
levels will be in the 5 to 20 pA range, with no
sample present and the GC oven cool (<100°C).
The FID background level is due to presence of
organic material in the carrier, makeup, FID air
and H
2
gases, and the amount of stationary
phase that is coming off of the GC column. For
successful GC work using FID, it is important to
observe the requirements for gas purity in the
6850 Site Prep and Installation manual. Minimum
gas purity should be 99.9995% or greater. Also
the FID temperature should be maintained at
least 20°C greater than the final oven temp of
the GC analysis. The FID should never be oper-
ated at less than 300°C.
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