I have 5977B.
When this happens it likely one of two scenarios,
1: A leak before the gas trap where carrier gas is leaking out and oxygen is diffusing in. The O2 will be scrubbed by the trap and the N2 will pass through.
2: A contaminated tank of carrier gas that has N2. This can show at any point in the gas tank depletion onece the lighter gas layer is becoming depleted.
Thanks for the reply,
We have checked for leaks several times and none were found. I’m leaning toward contaminated N2 tank but I can’t think of any way to verify that.
Again, thanks for your help
Try varying the carrier gas flow to see if you see a change in N2 abundance. For example if you are at 1ml/min, increase to 1.5 ml/ min and see if the N2 value goes up in the air and water check. This will confirm that the issue is with the carrier gas stream. It will still not give you complete confirmation of a contaminated tank. Changing the tank and purging the line may be your best bet.
Would cleaning the source possibly help? Last tune (5 min ago) still bad. Grasping at straws now…
A source clean will not help with N2 in the background, only the first two scenarios are the likely culprit .
I agree with others that a contaminated He tank or a leak prior to the gas trap could be the issue. Did you get this problem after changing to a fresh tank. I was also once told that if the trap is exhausted you can get some strange N2/O2 ratios
Have you changed gas trap lately ?
Have you purged trap ? That needs to be done thoroughly.
What happens if you bypass trap ?
We had this same issue. In the end we removed the gas traps completely and resolved the nigh nitrogen issue.
If you have a post-column splitter to a detector that uses Nitrogen for make-up, you can get Nitrogen into the MSD if flows are not balanced
I have seen this also happen in a newer lab where all the new plumbing has been purged with nitrogen. This could also be an issue if the tank is far away and the tubing has been pressure tested with Nitrogen. This is difficult because it can take several weeks for the nitrogen to purge out of the lines depending on the volume of tubing in line.
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