Detectors 5
Advanced User Guide 75
Selecting reference and makeup flows for the TCD
Sample components with higher thermal conductivities than the
carrier gas produce negative peaks. For example, helium or
hydrogen form a negative peak with nitrogen or argon-methane
as the carrier gas.
Chemically active compounds reduce TCD filament life
The tungsten-rhenium TCD filament has been chemically
passivated to protect against oxygen damage. However,
chemically active compounds such as acids and halogenated
Makeup gas flow, mL/min
Hydrogen
Helium
Nitrogen
Pressure (psig)
(kPa)
10
69
60
414
50
345
40
276
30
207
20
138
4
8
12
16
20
Table 13 Recommended flow rates and temperatures
Gas type Flow range
Carrier gas
(hydrogen, helium, nitrogen)
Packed, 10 to 60 mL/min
Capillary, 1 to 5 mL/min
Reference
(same gas type as carrier)
15 to 60 mL/min
See the figures to select a value.
Capillary makeup
(same gas type as carrier)
5 to 15 mL/min—capillary columns
2 to 3 mL/min—packed columns
Detector temperature
<150 C, cannot turn on filament
Detector temperature should be 30 °C to 50 °C greater than highest oven ramp
temperature.
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