Xevo G3 QToF – Strong background peak preventing calibration even with infusion OFF
Hi everyone! I’m troubleshooting a Waters Xevo G3 QToF and I’m having an issue that is preventing us from calibrating the instrument.
We are trying to calibrate with our usual calibrant, but there is a very strong background peak already present even before we introduce the calibrant. The background signal is strong enough that the calibrant peaks are overwhelmed/interfered with, so we cannot get a proper calibration.
The situation is:
- LC flow is OFF
- Sample infusion is OFF
- LockSpray infusion is OFF
- Both Sample Flow Control and LockSpray Flow Control show “Idle”
- Sprayer position = Sample
- However, we can still see what appears to be a continuous spray from the sample sprayer
- There is a strong signal on the QToF even though we have not infused calibrant or sample
- The major unexpected signal appears around m/z 60
- The signal is strong enough that when we try to introduce the calibrant, the background peak overwhelms the calibrant signal and we cannot calibrate properly
Current Fluidics settings are:
Sample Flow Control
- Infusion flow rate: 5.0 µL/min
- Flow state: Infusion
- Reservoir: C
- Status: Idle
LockSpray Flow Control
- Infusion flow rate: 10.0 µL/min
- Flow state: Infusion
- Reservoir: B
- Status: Idle
Sprayer position: Sample
I understand that the displayed “Flow State: Infusion” does not necessarily mean the pump is actively running because the actual status is Idle.
What is confusing us is that we appear to have continuous spray/background signal despite both fluidics being Idle.
Our main concern is that this is preventing calibration. We don't want to start replacing valves, tubing, or other consumables without knowing what is actually causing the problem.
Has anyone experienced this on a Xevo G3 QToF?
Could this be caused by:
- A fluidics valve not switching completely?
- IPA/wash solvent leaking or being routed to the sample sprayer?
- Residual pressure/solvent in the fluidics line?
- A divert-valve or fluidics routing issue?
- A problem with the sample fluidics pump/valve?
- Or could the strong m/z ~60 signal be coming from another source entirely?
What would you check first, and is there a way to completely stop/isolate the sample fluidics so we can determine where this signal is coming from?
I’ve attached a screenshot of our current Fluidics/Tune page. Any advice from anyone familiar with the G3 would be greatly appreciated.
