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The universal detector that detects everything: How does the thermal conductivity detector reveal the truth about gases?
In the field of scientific detection, the thermal conductivity detector (TCD) is known for its ability to detect everything and has become an important tool in gas chromatography (GC). TCD's high performance, non-specific and non-destructive design makes it perform well in a variety of applications. By comparing the thermal conductivity of a sample gas to a reference gas, such detectors can detect the presence of almost any gas, including organic and inorganic compounds.
The beauty of a thermal conductivity detector is that it can detect almost any gas, not just flammable substances.
How it works
The operation of TCD is based on an electric heating wire placed in a temperature-controlled detection chamber. When the sample gas flows into it, the heat conduction characteristics of the electric heating wire change. Normally, the heating wire emits a steady amount of heat to the detector body, but when the sample gas enters, since its thermal conductivity is lower than that of a reference gas such as helium or hydrogen, this will increase the temperature of the heating wire, thereby changing its resistance.
This change in resistance can be measured using a Wheatstone bridge circuit, which converts the signal into a measurable voltage change. When the thermal conductivity of the sample gas is reduced compared to the reference flow, a recognizable signal peak is formed on the detector. These peaks not only show what compound is entering the sample, but also indicate its concentration by its area.
This technology is not only sensitive to organic compounds, but can also detect various permanent gases, providing reliable data support for scientific research.
Precautions during operation
When operating the TCD, care must be taken not to interrupt the gas flow during spiral heating, otherwise the heating wire may burn out. In addition, some fluorine compounds may attack the passivation layer of the heating wire, so these substances should be avoided during use.
Although the detection peak of hydrogen will have negative fluctuations when using helium, this problem can be solved by using other reference gases such as argon or nitrogen. However, this choice reduces detection sensitivity for compounds other than hydrogen.
Application scope
TCD has a wide range of applications. In addition to using it to detect various gas concentrations in gas chromatography, it also plays a key role in many industries. Here are some of its main applications:
- Medical use: used in pulmonary function testing equipment.
- Energy Industry: Measure the calorific value of methane in biogas samples.
- Food and Beverage Industry: Quantify or verify food packaging gases.
- Oil and natural gas industry: Calculate the content of oil and gas components during the extraction process.
- Monitor hydrogen: Confirm hydrogen purity in the hydrogen cooling turbine generator.
- Medical Imaging: Detecting helium leakage in MRI superconducting magnets.
Through these various applications, thermal conductivity detectors not only play a role in the laboratory, but also take the stage in many key industries.
Conclusion
As a universal detector, the thermal conductivity detector (TCD) provides a valuable monitoring method for scientific research and industrial applications. Its ability to identify multiple gases simultaneously and its application in various market needs makes it an indispensable part of gas chromatography. Facing the changing environment and needs, in what direction should thermal conductivity detectors develop in the future?
