EFFECT OF AMMONIA CARRIER GAS ON THE RESPONSE OF THE FLAME IONIZATIONDETECTOR

The effect of using ammonia as a carrier gas on the response of the fl ame ionization detector (FID) has been investigated. It was found that the FID response, calculated as the effective carbon number (ECN), in creased for all the compounds studied when ammonia, rather than helium , was used. The change was 0-0.9 carbon atom far hydrocarbons, one car bon atom for alcohols and diphenyl ether, and 0.4-1 carbon atom for ph enols and ketones. The increase in ECN was larger for amines (0.8-5 ca rbon atoms), but these numbers also reflected an improvement in chroma tographic performance as a result of reduced adsorption on the column. The largest change in signal-to-noise ratio, a six-fold increase, was obtained for octylamine; ratios for hexyl methyl ketone, diisobutyl k etone, dihexylamine, dibutylamine, and N-methyloctylamine increased by a factor of 2-3 when ammonia was used as carrier gas. To determine th e extent to which the effect on detector response was solely attributa ble to ammonia, a mixture of 5 % ammonia in nitrogen was used as detec tor make-up gas with helium as carrier gas. Under these conditions the noise in the FID increased but for most of the compounds studied the signal-to-noise ratio also increased.