Carbon Dioxide (m/z 44) in My Mass Spectrometer, Normal? Leak? or Other?

I hate to lose. When Jack Cochran informed me that you can’t run EPA 8270 GC/MS when CO2 (m/z 44) is higher than the column background (m/z 207) I felt pretty confident I had him. P&T water samples can contain pretty high levels of CO2 so it was just a matter of finding an example to prove him wrong. I found a high temp run where m/z 44 was higher. The 360°C analysis without the column flying apart is proof that there is no oxygen in the system. It did not take long to determine that I had just as many examples that proved quite the opposite. So what is going on? After careful examination of the lab books it appears to be related to how long the instrument has been pumped down following a column installation. While there may not be a leak, it’s not good practice to run with m/z 44 as an interference that will affect sensitivity, so make sure your system is adequately pumped down (especially before tuning)....I guess Jack got me again. Oh yes...and the answer: Other.