178 Advanced Operation Manual
5 Detectors
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
Tabl e 45 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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