Aux EPC or PCM for Collision Gas 7890/7200

There will always be measurable oxygen - or at least I've never seen a QTOF with none.  On a 7200A, one week is barely pumped down. We recommended two weeks between installation and checkout.  Getting all of the molecules off that are adhered to the walls of the flight tube takes time.  For every molecule flying around there are ~500 adhered to all of the surfaces.

The collision cell is part of the magic. Gas on and gas off totally changes the way it functions and totally changes the way the QTOF system calibrates. You cannot necessarily troubleshoot this like a single quad system.

The entrance lens is not part of the Removable Ion Source, it is inside on the analyzer. To clean it means venting, removing the source radiator, removing the entrance lens, cleaning it, and going backwards to reassemble. 

Wow, I wish I had posted earlier in the process because you have been a tremendous help - I probably could have saved a week if I knew all this beforehand. 

That all makes a lot of sense. I just finished the one hour bakeout and here's how the EI calibrant spectrum looks:

Pretty happy with that signal for now anyway. The transferline is just capped off from when I split the system to try and track down if/where it was leaking so I still need to reinstall the column and 7890 but do you recommend letting it pump down for a few more days before we test/tune/calibrate everything?

Yes, wait longer, especially since you just cleaned the source.   You might get a no-column-flow tune out of it maybe Monday?  The spectral tilt, the relative abundances of 69/131/219/502 won't be ...right... with no column flow, but if they are there and the resolution is even sort of good, I'm impressed it got this far. 

Is there a way to zero or calibrate the CC gas EPC module? I noticed an offset flow value that seems to affect N2 and He readings. I’ve already attempted to zero the flow using the instructions provided in a previous post 'How to Zero a Flow or Pressure Sensor in EPC Modules', but I haven't had any success. Could anyone provide further guidance on how to resolve this issue or suggest additional troubleshooting steps?

Hi, how big is the offset? If the zeroing didn't work, and the offset is a consistent value, my initial gut reaction is that it sounds like a problem with the epc module. Was it working before and this issue just started or are you setting it up new and having this problem?

Can you try increasing or decreasing the pressure at the regulator on the tank and seeing if the value changes? If it changes with pressure, that would definitely point to an actual hardware issue with the gas block, but if not it's much more likely to be a sensor or software issue.

Thank you for your suggestions!

The offset flow is currently reading around 1.3 mL/min for the quench gas (He) and 1.1 mL/min for the collision gas (N2). Since I’m setting up a pre-owned instrument, I don’t have any detailed information on the previous settings or conditions.

I tried adjusting the pressure on the tank as you recommended, but unfortunately, it didn’t have any noticeable effect on the offset flow.