Posted: Mon Feb 06, 2006 12:18 pm
What sort of GC are you using that needs a make up gas to get FID to work ? 
Standard capillary columns operate at about 2ml/min, micro columns for fast GC may be 0.1-0.5ml/min not a big flow difference when you are looking at 300ml/min of air and 30ml/min Hydrogen. A good FID design does not need make up gas 
. Use of Nitrogen make up can be used to optimise the flame for the most sensitivity however the difference is not great. I thnk that at one time at least one gas supplier provided special Nitrogen enriched FID air here in the UK, I do not know if many used it and if it is still available.
Standard capillary columns operate at about 2ml/min, micro columns for fast GC may be 0.1-0.5ml/min not a big flow difference when you are looking at 300ml/min of air and 30ml/min Hydrogen. A good FID design does not need make up gas . Use of Nitrogen make up can be used to optimise the flame for the most sensitivity however the difference is not great. I thnk that at one time at least one gas supplier provided special Nitrogen enriched FID air here in the UK, I do not know if many used it and if it is still available.