Detectors 5
Advanced User Guide 77
3 Verify that makeup gas type is the same as that plumbed to
your instrument (next to Makeup line in the parameter list).
Change the gas type, if necessary.
4 Set the reference gas flow rate.
5 If you are using packed columns, turn off the makeup gas (or
proceed to step 6 and enter 2 to 3 mL/min, see “TCD carrier,
reference, and makeup gas” on page 73) and proceed to step
7
6 If you are using capillary columns:, choose a flow mode and set
the makeup gas flow or combined flow.
7 Turn on the filament. Allow about 30 minutes for thermal
stabilization. A longer period may be needed for the highest
sensitivity.
8 If necessary, turn Negative polarity [On/Yes] to invert
negative-going peaks. When a sample contains components
giving both positive- and negative-going peaks, Negative
polarity can be switched on and off during a run as a
timetable event.
Example: Packed mode (packed and large capillary columns)
Column flow is 15 to 60 mL/min. Set the reference flow to 1.5
times the sum of column flow + makeup flow.
Makeup gas is recommended with all capillary columns. It
allows the column to be inserted all the way into the detector
and withdrawn 1 mm. If makeup is not used, the column must
be no more than 3 mm above the ferrule. Minimum makeup flow
is 1 mL/min.
1/8-inch stainless steel column If column flow is 30 mL/min,
set the reference flow to 30 × 1.5 = 45 mL/min. Total detector
flow is 30 + 45 = 75 mL/min.
10 m × 0.53 mm column If column flow is 15 mL/min and
makeup flow = 2 mL/min, set the reference flow to 1.5 × (15 + 2)
= 25.5 mL/min. Total detector flow is 17 + 25.5 = 42.5 mL/min.
Example: Capillary mode (small capillary columns)
If combined column plus makeup flow is between 5 and
10 mL/min, set the reference flow at 3× the combined flow. For
a combined flow between 10 and 15 mL/min, use a multiplier of
2. This will bring the TCD within 25% of the maximum response.
For further optimization, adjust the reference flow.
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