Thermal Conductivity Detector

1. Thermal Conductivity Detector

2. Introduction • Thermal conductivity detectors have been in use since before the beginning of gas chromatography. • Compares the thermal conductivity of two gas flows – the pure carrier (reference) gas and the sample..

3. Uses • Thermal Conductivity Detector used to analyses inorganic gases (Argon, Nitrogen, Hydrogen, Carbon Dioxide, etc) and small hydrocarbon molecules.

4. Detector component

5. Detector component • Tow cells with small volume termed as: • Reference cell • Sample cell • Each cell has a resistance wire or thermistor or filament that posses a high temperature co efficient or resistance.

6. Principle

7. Principle • The sample components in the carrier gas pass into the measuring channel. • A second channel serve as a referencechannel where the pure carrier gas flows. • Electrically heated resistance wire are located into both channels.

8. Principle • The difference in thermal conductivity between the column effluent flow(sample components in the carrier gas ) and the reference flow of carrier alone, produces a voltage signal difference proportional to this difference. • This signal is proportional to the concentration of sample components.

10. Sensitivity • The sensitivity of TCD response to various solutes is dictated by the solutes' thermal conductivities relative to the carrier. • This makes TCD respond universally without dependence upon specific chemical elements or structures.

11. Advantages • Ease and simplicity of use. • Broad application to inorganic and organic compounds. • Its nondestructive character, which permits collection of solutes after detection.

12. Disadvantages • The chief limitation of the thermal conductivity detector is its relatively low sensitivity.

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