High Nitrogen after tunning

[GCMS_YE]

my GC-MS (5973) has shown high N2, the ratio to O2 is over 10, somtimes, N2 becomes the base peak after DFTPP tuning. At least no apparent leak as I can see. is this a carrier gas issue (UHP helium) or still a leak in somewhere? Anyone can tell me?

[rb6banjo]

Have you tried a different tank of carrier gas? I had this issue a while back and it turned out that the tank was contaminated with N2.

[Yama001]

It is worth checking if it looks the same after a standard autotune is run; I have seen odd tunes over emphasize the gases on occasion - though N2 as the base peak is pretty out there. I believe the air and water check utility will ask if you want to reset to standard conditions (or some such phrasing) for the same reason.

[twranger]

We had this problem last year, switched tanks which didn't help, went to change the trap and discovered one of the swagelock fittings had been installed incorrectly (for years?!), don't know why it showed up suddenly. Also thought it was curious that it was just nitrogen that showed up, little water/oxygen.

[James_Ball]

Is your Helium cylinder below 500psi? Sometimes when it gets near empty you will find that N2 has settled to the bottom of the cylinder.

Also take some canned air which is a fluorocarbon and spray it around your side plate seal and see if it shows up when scanning with the PFTBA valve closed. It is really easy to get a small piece of lint on the o-ring and have good vacuum but still have a leak large enough to see N2 as the base peak.