Chromatography Forum

i work on agilent gcms and varian
but in agilent gc ms i have high n2 and low o2 and every i do it not chang
what can i do wan do u find any about that

What carrier are you using?

Before doing troubleshooting. Be sure that you have kept the routine maintanace up to date (fresh septa, tight ferrules, etc.) and that you are using the correct supplies, including the grade of carrier gas.

Low oxygen in a mass spec when you are using hydrogen carrier may not be telling you much. You may need to check over the mass spec with "dust-off" or a similar product.

If you are using helium, and you have noticible m/z 28, there are a coiuple of possibilities:
- Air present is coming in the carrier stream, either lower grade helium than you shoud be using or therere is air in the system passing over a trap that removs oxygen. (If you are not careful when changing gas cylinders, you can get a bit of ailr in the line - which can be removed by bleading the lines at the back of the instrument(s) on the gas line.
- m/z 28 can be generated by decomposition of a stationay phase. While I have seen it mentioned, I have not encountered this myself -- and I do nor remember which stationary phase(s) should give m/z 28 as a decomposition product.

What mode is the inlet in? Splitless? If yes chage it to split and check the air and water.

I agree with Don, your carrier gas scrubber may need changing.

What MS are you running?

H2 as a carrier is a major problem for anything older than a 5973, and many times the problem manifests itself as amu 28/14. It is not real - it is especially problematic, for some reason, on the 5972.

If you are running older than a 5973 and are using He carrier, you may be looking at quadrupole issues - both the 5971 and the 5972 had quad stability issues with the glass quads, and you get "ghost" masses, one of which is 28.