Effect of the Carrier Gas on the Sensitivity of Thermal Conductivity Detectors in Gas Chromatography

Abstract

IT has recently been suggested¹ that the use of argon or other carrier gases of low thermal conductivity will lead to increased sensitivity of thermal conductivity detectors used in gas Chromatography. While this may be so in certain special cases, it is by no means a general effect, and it is the purpose of this communication to point out some of the many disadvantages of carrier gases of low thermal conductivity. The effects we wish to discuss may be illustrated qualitatively by the use of the approximate equation¹ for the variation of filament temperature (t) with composition (x) of the eluted gas. where k₁,k₂ are the thermal conductivities of the carrier gas and organic vapour respectively. Substituting the thermal conductivity data from Table 1 in equation 1 leads to the predicted relative sensitivities shown in Table 1. The substances investigated, benzene, n-heptane, chloroform, carbon tetrachloride and methyl chloride, would appear from Table 1 to show a higher sensitivity with argon than with helium but ethanol would show a lower sensitivity, and methanol would show a peak reversal compared to ethanol. It should be pointed out that these estimates are only crude approximations since the initial temperature of the detector filament is unknown and is probably considerably higher than 100° C. for our apparatus in which the block temperature is 100° C.