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3. Eliminate the column/carrier as the source of
noise (background). Remove the column from
the FID and cap the fitting (an easy way to
do this is to cut the column below the detec-
tor fitting and plug the end of the column
extending from the FID by pushing a septum
over the column edgewise).
4. Relight the flame. Allow it to stabilize and
reevaluate the noise. If the FID noise
becomes acceptable, the problem could be
due to contaminated carrier gas or excessive
column bleed. If the problem persists, con-
tinue the procedure. Otherwise reevaluate
with a known good, thin, well-conditioned,
film column (an uncoated retention gap is a
good troubleshooting tool to isolate column
bleed problems).
Released: April 2004
5. Measure the FID flows with an independent
6850 Series Gas Chromatograph Service Procedures
measurement device such as a bubble meter
or electronic flow meter. Use the FID flow
adapter (part number 19301-60660). The
recommended flows for the FID are:
Column or Column+Makeup: 30 mL/min
H
: Equal or > Column or Column+Makeup
2
if using capillary column (optimum FID signal
to noise performance is achieved at about a
1:1 ratio of H
to inert gas)
2
Air: 400 mL/min
299
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