text: gc detector selection? i have an ethylene stream with a lot of trace impurities in it.  for all of them except ammonia i can use a gas chromatograph with a fid (flame ionization detector).  in the case of ammonia a fid will not work.  what type of detector would be best suited for ammonia (5-0.1 ppmv range).  i also looked at a npd (nitrogen phosphorus detector) but it seems to only be good for nitrogen containing organic compounds.  any help (and sources) would be appreciated. the best bet is for you to contact a local college even a junior college will do and ask to speak to the chemistry dept. chair or one of the organic chem. teachers on staff.  i think that will give you them most reliable results, and it is probably safier to ask a professional about something as expensive as a gc.