GC/IRMS Thermo Delta V High Mass 18 & 30

[segaloco]

Ever since our repair tech last maintenanced our instrument, we've been getting unusually high background noise at mass 18 and mass 30, indicative of water contamination. However, checking through all our equipment so far, we haven't found any potential sources except possibly a Werther P 50 TC AL compressor being used in the system.

Has anyone here encountered this issue before, and if so, how did you solve it? We really need to get this instrument back online ASAP, and any help would be greatly appreciated! (Don't worry, we are calling another tech too, but they've been giving us the runaround saying that contamination on those masses isn't problematic, but our numbers say otherwise)

[CE Instruments]

First isolate the problem. Is it in the MS or do you only see it when the GC is in line ? Isolate each item as much as you can it will make it much easier to find the source of these masses

[trozen]

segaloco,

what are the absolute values at m/z 18 and 30 (at the middle cup) and does it go back to normal when you close the needle valve?

[segaloco]

Sorry for the late reply. We've resolved the issue now, there was residual contamination in the MS itself. Even with the ConFlow valve turned off we were getting around 1700 counts for mass 18 (as the middle cup). As for 30, it would change as runs continued, starting low and growing towards the end, which I was told is indicative of NO2 forming. Thank you for the replies, we had to bake the MS out to relieve the contamination, our numbers have been better now. The main issue was that the contamination at 30 was messing with nitrogen linearity checks (the slope technically passed Thermo's Spec, but the r^2 was so bad that it just didn't feel right to accept in that condition)