Chromatography Forum

I am setting up an FID. I am considering using a tank of compressed zero air as the air supply. My concern is that not all zero air has exactly the same ratio of oxygen to nitrogen. Would this potentially cause problems with FID performance when installing a new tank, or is it a moot point?

Thanks.

I wouldn't worry about it. First of all, if it's "air", the N2/O2 ratio can't vary by that much. Second, any calibration plot is only valid for a single day/tank/column/etc. in any case, so minor variations will cancel out.

I ran across this link by accident while looking for somehting else:

http://www.parker.com/balston/AGS/Engli ... Purity.pdf

Surprisingly, this shows that different sources of pure air give different FID performance. The author does not explain how this could happen, and it is from a commercial source, so take it for what its is worth.

Peter

I am setting up an FID. I am considering using a tank of compressed zero air as the air supply. My concern is that not all zero air has exactly the same ratio of oxygen to nitrogen. Would this potentially cause problems with FID performance when installing a new tank, or is it a moot point?

If you didn't use zero air, what would you use? Ambient air pushed through a compressor is going to have large and varying amounts of hydrocarbon contamination that will cause much greater variation in your baseline than the variation caused by different oxygen concentrations in zero air in cylinders.