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The recommended gas flows for the 6850 FID
are:
Carrier, packed columns: 30 to 60 mL/min
Carrier + Makeup, capillary columns:
30 mL/min
H
: set equal to or > the total carrier/makeup
2
flow
Air: 400 mL/min
Measure the flow rates for each gas indepen-
dently:
a. Cool the GC oven and turn off the inlet
pressure/flow to stop the column flow. If
there is any doubt as to column leaks, or
you are using a wide bore column,
disconnect the column and cap the FID
column fitting.
Released: April 2004
Table 1-1
flow rates.
6850 Series Gas Chromatograph Service Procedures
b. Turn on H
only and measure the actual
2
flow rate. It should be within 10% of
setpoint.
c. Turn off H
, turn on the Makeup gas and
2
measure the actual flow rate.
d. Turn on the H
flow and measure the
2
two gases together. The resulting actual
flow should be exactly the sum of the
two previous measurements. If it is
lower this could indicate a leak in the
column fitting at the detector base or a
partially plugged jet.
e. Turn off H
and Makeup gas flows. Turn
2
on the Air flow and measure the actual
flow rate.
lists reasons and solutions for low FID
307
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