Chromatography Forum

Hi everyone,

Currently I am facing a problem in FID. When I inject fresh air in GC, I have got CO and CO2 peak in FID. I am using TCD-Methanizer-FID in my system. I concern, if CO and CO2 come from air, it will effect my result where I analysis CO and CO2 as a major product from my feed. I don't know how FID detect air. Is it a problem in my column (HayeSep D) or problem in methanizer catalyst or anything else.

Thanks.

I do not know what part of the world you are in and what news you watch, but a lot of the world are concerned with global warming. Much of this is due to the carbon dioxide levels in the atmosphere which is well over 300 ppm. So yes, you will see CO2 when you inject air.

The carbon monoxide is a different story. CO and O2 will coelute on the HayeSep D column. If the catalyst has become partly carbonized due to high concentrations of hydrocarbons passing through it, the carbon will react with the O2 to form CO and CO2. This will in turn be converted to methane which is then detected by the FID.

Depending on how much carbon is in the catalyst, you can try to burn it off by injecting large volumes of air, otherwise you will need to replace the catalyst bed.

Gasman

How big are the CO and CO2 peaks, and how did you confirm their identity?

I agree with everything Gasman said, I only add that air gases will make a tiny 'peak' where CO elutes just from the air hitting the FID. So if you are talking about a tiny peak, then no problem.

Atmospheric CO2 is 400ppm now and counting...