Detectors 5
Advanced User Guide 69
The default setting for Lit offset is 2.0 picoamps. This is a good
working value for all but very clean gases and systems. You may
want to lower this setpoint if the detector attempts to reignite
when the flame is still on, thus producing a shutdown.
To change Lit offset:
1 Press [Config][Front Det] or [Config][Back Det].
2 Scroll to Lit offset.
3 Enter the new value and press [Enter].
Recommended starting conditions for new FID methods
See Table 12 for guidelines and rules to select initial detector
settings for new methods.
Table 12 Recommended starting conditions
Combustible gas mix Make sure that the final hydrogen-to-air ratio is between 8% and 12%
Detector temperature Set to 20 °C above the highest oven temperature, depending on the column type.
A temperature of 300 °C provides a good starting point and easier ignition, and
minimizes water condensation.
The GC will not attempt to ignite the flame at a temperature <150 °C.
Carrier gas flow (hydrogen, helium,
nitrogen)
Packed columns Suggest 10 to 60 mL/min
Capillary columns Suggest 1 to 5 mL/min
Detector gases Flow range mL/min Suggested flow mL/min
Standard installation
Column plus capillary makeup 10 to 60 30
Hydrogen 24 to 60 30
Air 200 to 600 400
With Nickel Catalyst Accessory:
Standard installation
Column plus capillary makeup 10 to 60 30
Hydrogen 24 to 60 30
*
Air 200 to 600 400
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