Chromatography Forum

When I worked with an air bottle, my background noise was around 20 pA with the FID detector.
I changed the air bottle with an air compressor with many filters. The background noise reached 200, so I guess my air was contaminated.

I switched back to the air bottle, nothing changed. I heated all the system at high temperatures and I changed the FID buse, still no changes. At last I changed my column by a new one, but the background noise was still around 200.

I'm running out of ideas... What could I do to go back to my former background noise at 20 pA?

New filters within date ? My guess would be that something from the compressor or the new (?) lines got into an existing line and contaminated it. What ever you try you will still see it until you eliminate the contamination. Hope it's not now in the GC pneumatics.
For an air line from a compressor I would only ever use a Hydrocarbon filter what else have you in line ?
Should be something fairly volatile so should clear on it's own after a while if you eliminate the source.

Here's hoping you did not use spray PTFE on the joints as one customer did it takes years for the solvents to clear you are better off throwing away the contaminated lines.

Did you use chromatography grade copper? If not you can try removing it and rinsing with MeCL2 or some other solvent.

As long as the 200 pA background is constant (i.e. no short-term noise) then it might not have any effect at all on system performance. Just autozero the detector.

Peter