IHERMAL CONDUCTIVITY DETECTOR (TCD)



GC-TCD commonly used in the analysis of permanent and inorganic gases because it responds to all these substances unlike the FID, which cannot detect compounds which do not contain carbon-hydrogen bonds. TCD detects any species that differs from the carrier gas in thermal conductivity – essentially any gas, given the right carrier. It works by having two parallel tubes both containing gas and heating coils. The gases are examined by comparing the heat loss rate from the heating coils into the gas. Normally one tube holds a reference gas and the sample to be tested is passed through the other.  Using this principle, a TCD senses the changes in the thermal conductivity of the column effluent and compares it to a reference flow of carrier gas. Most compounds have a thermal conductivity much less than that of the common carrier gases of hydrogen or helium. Therefore, when an analyte elutes from the column, the thermal conductivity of the effluent is reduced and a detectable signal is produced. Others, TCD also can be used for initial determination of unknowns, water and solvents analysis, aggressive acids and amines​, trace ammonia in gas samples.

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