Thermal Conductivity Detector (TCD)

Thermal Conductivity Detector (TCD) is a detector used in gas chromatography (GC) to analyse inorganic gases (such as argon, nitrogen, hydrogen, carbon dioxide) and small hydrocarbon molecules. The TCD compares the thermal conductivity of two gas flows, the pure carrier (reference) gas and the sample. Changes in the temperature of the electrically-heated wires in the detector are affected by the thermal conductivity of the gas that flows around them. The changes in this thermal conductivity are sensed as a change in electrical resistance and are measured.

As commonly used with other GC techniques, a carrier gas is required with low water and oxygen impurities, since water and oxygen can interact with the stationary phase and cause significant problems such as high baseline noise and column bleed in the output gas chromatogram that both reduce the analyser sensitivity and decrease column lifetime. In addition, oxygen and water impurities in the detector gas can affect the TCD as they can cause oxidation of the detector wires.