Chromatography Forum

We are dealing with the nationwide issue of low helium supplies. I switched over to UHP nitrogen in my Varian 3800 GC - MS (2000) yesterday and pumped down overnight. In the column parameters, I made sure to switch the inlet I'm using from Helium to Nitrogen. Is there anything else I need to do? The inlet is maintaining pressure well but I certainly can't pass an air/water check, and I don't think the the problem is a leak. When I attempt an autotune, it can barely detect 69 m/z and all the calibration masses are way off calibration (i.e. it's detecting 131 at 135, etc). Any suggestions for using nitrogen as a GC-MS carrier gas?

-Aaron

Why not try H2?

N2 can be ionized at 15.5 eV, which is a lot lower than that of He(24.8 eV) and H2(18eV). That can cause a lot of problems when using EI. This topic had been talked about in the forum.