Normal background levels on Waters Xevo TQ-S?

[syntel]

We have a Waters Acquity UPLC/Xevo TQ-S (new instrument to me) and we are seeing very a very high background noise injecting pure solvent/mobile phase (5 to 6e5 TIC). We have rinsed the UPLC using the recommended solvents, and doing direct infusion via the IntelliStart-fluidics gives the same result. I have no real idea of what has been injected into the system previously. The cone has been cleaned. Any tips on what I should look at next? We're using proper solvents.

[dr_bahram1977]

Hi
Let us know what are you doing? If you're scanning in 100-500 amu range, this can be normal. If you're doing MRM on a specific Ions, this is not good.

[syntel]

Thanks for your reply,
Currently I'm doing a regular UPLC -> TIC LC-MS scan to determine the ID/retention times for different analytes. Latter on, it will be purely MRM work. Yesterday I managed somehow to get the system "clean", with a pretty OK baseline using 100% CH3CN, but today it looks like the noise is back up again (waiting to see if it stabilizes now). So the culprit might be the H2O we're using (MilliQ). I understand that it's a sensitive instrument and since the guy who worked with it previously left I can't really compare the background levels with anything. Sometimes it goes up to 1-2e8 which really shouldn't be normal, right? Even when doing full scans. Talked to Waters as well, and they say the system might need a good cleaning.

[dr_bahram1977]

Do a low range scan ( 50-150) and see which ions are dominant. then you can guess what is main source of problem. then, do a high range scan ( 500-150) and see if there is a big ion there or not.

[Gaetan Glauser]

Hi,

We never analyze in full scan mode on our TQ-S, only in MRM. However, before we start an acquisition, we check noise on the tune page at 95% H2O (+FA 0.05%). The scan time is set at 0.4 s and the range is 100-1000 Da. The biggest peaks are in the 10e7 range, so I am not that surprised about your background noise.