Date: Tue, 1 Apr 2025 18:22:50 +0000 (UTC)
Hi Emily,
Just my $0.02... I figured I'd throw some other possibilities out there
that nobody had mentioned. Alternatively, if nobody else has mentioned
them, it's entirely possible that they're complete nonsense.
How do your new shim maps look? If you regenerate shim maps and your
shims aren't at least decent, you get cruddy shim maps, so gradient shimming
doesn't work so well.
Has the pressure in the magnet dewar changed? i.e. if you had a check
valve on the exhaust before and then you removed that and have some sort of
back pressure from the recovery system, this could cause your shimming to
change. It might be worth looking into that in more detail if the
suggestions from everybody regarding reducing vibrations don't make a big
difference.
Alternatively, if the "new" back pressure, whatever it is, is relatively consistent
then maybe you do just need to shim your magnet up manually to adjust for the changes.
One other detail that I'm not sure will make a huge difference but it is more magnetic
stuff in the magnetic field--a lot of KF clamps I've run into have magnetic screws.
And I'm not sure about the rest of the fittings that got installed on the helium manifold.
The stray field is typically not as well shielded above the bore and if you're seeing effects
in off-axis shims, those parts are in an off-axis location, no? This might just be
something you have to put in some time and shim out. As long as they're not moving
around you should be able to compensate for them if they are the cause.
Cheers,Mike
On Tuesday, April 1, 2025 at 11:03:18 AM MDT, Emily Crull via groups.io wrote:
Hi everyone,
I'm still working on familiarizing myself with VNMRJ 4, and our Agilent has recently
encountered what is presenting as a shim based issue. Over our spring break
(Mar 16th-22nd), we had the hook up for our incoming He collection system installed
(featured in the picture). Since that occurred, we have been having noticeably broader
peaks in the 1H NMR spectra and simply running Z-gradient shims isn't fixing the issue.
This is appearing even in the Ethylbenzene standard we have. We're just seeing humps
with no resolved coupling at all.
Here's what I can say about the magnet itself:
- Based on the coin level I put on top of the bore, it is level, so the
legs appear to be keeping up with the added weight from the install.
- The magnet is from 2012.
- We haven't seen a change in our Helium consumption. Our Nitrogen meter
only registers in 5% increments and it's drop rate didn't change at all either.
- I believe I have updated the shim map using a house made D2O standard,
but the issue still persists. The last shim map was from 2020
- The default "Gradient shim" button in VNMRJ that appears next to the AutoLock
and AutoTune is not improving the peak shape.
- Using the Autoshim drop down menu and selecting "Z-gradient and 4 non-spin shims"
was sometimes resolving the issue.
- The issue is not limited to one account and is being observed on the admin account as well.
Any feedback on other ways to troubleshoot the issue and/or resolve it would be greatly
appreciated. If any other information would be useful in diagnosing the problem, let me know
what it is and I'll try and find it.
Many thanks,
Emily CrullDirector of Chemistry Shared Instrumentation
emily.crull_at_mail.wvu.edu
West Virginia University
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