Chromatography Forum

I was looking for information re. FID makeup gases and how they can improve/disimprove sensitivity. We are currently using helium, as it is the only gas plumbed for use as makeup gas. I was told that using nitrogen or other alternatives can improve sensitivity, I was hoping to find out more about this, why it occurs etc. Any information or a related website (apparently difficult enough to find) would be a big help.

Using nitrogen as a makeup gas will generally give an improvement in sensitivity. The design of the FID also affects the amount of improvement.

In general you want to run the FID so that it is fuel starved and will produce the largest amount of unburned fuel (ions) as possible.

A lot of research has been done (almost all of it proprietary in nature) in adjusting hydrogen and air flows and different makeup gases. I could tell you more but as they say in the spy movies, then I would have to eliminate you. Sorry I cannot elaborate more.

Experiment using nitrogen as makeup and see how much you can improve sensitivity while also adjusting your hydrogen flow.

It may not be worth your trouble or the cost of the additional gas supply installation.

The old Varian 3500 had a FID that was 4 to 10 times more sensitive than that of its competition in its day. Today, I do not know if there is much difference between manufacturers but I hear rumors that a company with initials P and E has improved theirs considerably. Is it better than the rest? I don't know.

Specification comparisons are difficult to evaluate as any FID can be optimized for any one analyte and sometimes the noise factor is not considered realistically in publications.

best wishes,

Rod

Hi Anthony

Check the thread launched by Tony on Jan 4 2006.

Peter