Carrier Gas

If the gasses are know and only their proportions are being measured, then you should be fine.

If the gasses are unknown, a mass spectrometer in lieu of a katharometer may be indicated.

The h2 is run absent the process gases as calibration....it is then the comparison that determines specific gas volumes of known process gases....

"It functions by having two parallel tubes both containing gas and heating coils. The gases are examined by comparing the rate of loss of heat from the heating coils into the gas. The coils are arranged in a bridge circuit so that resistance changes due to unequal cooling can be measured. One channel normally holds a reference gas and the mixture to be tested is passed through the other channel."

http://en.wikipedia.org/wiki/Thermal_conductivity_detector

Hydrogen from your sample can overwhelm your thermister when pure hydrogen of your sample crosses over the thermister. To avoid this use a carrier gas that is approximately 7 % Hydrogen in Helium. You will effectively measure the difference between your carrier gas background hydrogen and the samples' hydrogen as the base line for your chromatograph will include the 7% H2 in the carrier.