Answer :

In gas chromatography, a thermal conductivity detector (TCD) is used to detect gases by measuring changes in the thermal conductivity of the carrier gas when a sample is injected. For TCD to function optimally, it's important to choose carrier gases with the right properties. The two carrier gases of choice for use with a TCD are:

  1. Helium

  2. Hydrogen

These gases are preferred due to their high thermal conductivity. Here's why they are particularly suitable:

  • Helium is chemically inert and provides a high level of sensitivity because its thermal conductivity is much higher than most sample gases. This differential makes it easier to detect the presence of other compounds as they alter the overall conductivity when they pass through the TCD.

  • Hydrogen, like helium, is also valued for its high thermal conductivity, which is even higher than that of helium. It can provide high sensitivity and is relatively cost-effective compared to helium. However, it's flammable, so safety precautions are necessary.

Using these gases ensures that the background noise in the detector is low, which in turn enhances the ability of the TCD to accurately detect and quantify different compounds in a sample. This makes them the standard choices in many laboratory settings where gas chromatography is used.

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