Effect of the Carrier Gas on the Sensitivity of a Thermal Conductivity Detector in Gas Chromatography

Abstract

IT appears to be a popular belief that the use of hydrogen or helium as the carrier gas in gas Chromatography gives the highest sensitivity with a thermal conductivity detector, because the difference in thermal conductivity between organic vapours and hydrogen or helium is greater than for any other carrier gas^1,2. This is not necessarily true, however, for the difference in temperature between the hot wire (at t ₁° C.) and the body of the thermal conductivity cell (at t ₀° C.) is inversely proportional to the thermal conductivity K ₁ of the carrier gas: , where a is constant. If the concentration of organic vapour in the carrier gas is x, the sensitivity of the detector is proportional to: When x is small, dK/dx is approximately equal to K ₁–K ₂, where K ₂ is the thermal conductivity of the organic vapour.