Detectors, Chromatography, Gas, Thermal Conductivity

Definition : Chromatography detectors designed to assess the individual molecules that come out (i.e., elute) from the chromatography column of a gas chromatography (GC) system by assessing the reduction in the thermal conductivity of carrier gas (e.g., nitrogen, helium) caused by the sample components (i.e., a thermally controlled detector [TCD]). TCDs have two channels lined with heated tungsten wire in a temperature-controlled cell, one channel for the effluent to pass through and the other for the carrier gas. The difference in resistance between the reference side (carrier gas) and the effluent side, that are components of a modified Wheatstone bridge, produces a current flow that is amplified by an electrometer which output is sent to a computerized system. The system, including an appropriate software, can display a chromatogram showing the constituents of the sample with an amplitude proportional to the quantity in the sample. TCDs are essentially universal and can be used to detect any components which thermal conductivities are different from that of the carrier gas.

Entry Terms : "Katharometers" , "Thermal Conductivity Gas Chromatography Detectors"

UMDC code : 33817

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