THERMAL CONDUCTIVITY
MEASURING INERT GASES IN A BINARY MIXTURE
The Thermal Conductivity Detector ( TCD ) consists of an electrically heated Wheatstone bridge in a temperaturecontrolled cell . For GC-TCD applications , the carrier gas ( helium ) is passed over the reference arm of the bridge , and the column effluent passes over the analyte arm under the same conditions for flow rate and temperature .
When no impurities are eluting from the column , the heat loss from the analyte arm matches that from the reference arm . When an analyte elutes from the column , it affects the thermal conductivity , changing the electrical resistance , which can be measured as a signal .
Thermal Conductivity is a robust technique for determining the concentrations of gases in a binary mixture . The Thermal Conductivity detector is a universal sensor . Analytical methods involving a TCD can be used where the constituents of the binary gas are known , such as in GC-TCD .
THE THERMAL CONDUCTIVITY SENSOR
P90