Biochemical Techniques and Instrumentation

2.6.3.6.4. Thermal Conductivity Detector (TCD)

Thermal conductivity detector consists of two pairs of electrically heated wire or thermisters. They are placed at the exit of reference and sample columns. The two thermisters will be connected to a balancing bridge. When only the carrier gas passes through the column, the thermal conductivity of the thermisters will be same and there will not be any imbalance in the bridge. When sample is applied, the sample components will be eluted one by one in the effluent gas, which will bring about changes in the conductivity of the gas surrounding the thermister in the sample column. This change in conductivity will change the resistance of the thermister causing an imbalance in the balancing bridge. This imbalance is amplified and fed to a strip chart recorder to give the chromatogram. Thsi detector is not as sensitive as other detectors but it is non-specific and non-destructive.