Is this a leak, contamination, or something else...

[wenleonard]

A couple of days ago the GC-MS was working just fine. Then I checked on my data files from the overnight run and got this noisy baseline.

https://drive.google.com/file/d/0B7ZnVv ... p=sharing

I did a bake on the column, transfer line and MSD, then tuned and still have this readout. I ran an air and water check and a tune evaluation and both indicated that my nitrogen oxygen ratio were low.

https://drive.google.com/file/d/0B7ZnVv ... sp=sharing

However the air and water check has a large hit for 40, I suspected a contaminated Helium cylinder and switched it but no change occurred. What could be causing this?

[rb6banjo]

Did you get a new delivery of helium recently? Perhaps all of the tanks are contaminated with argon? I had this happen a little while back but when I switched tanks, it went away. Only one tank was contaminated. Perhaps you got a suspicious lot of tanks?

[wenleonard]

It is a possibility. I had two tanks with water contamination a couple months ago. Thanks!