The other comments on the probe being off center are a good place to start.
We had issues like this and it took awhile to figure out.
Good luck!
Jeff
________________________________
> From: main_at_ammrl.groups.io on behalf of daveonofrei via groups.io
> Sent: Tuesday, October 10, 2023 5:48:46 PM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] Shimming From (almost) scratch on Varian
Thank you to everyone to responded to my last question. I have been trying
to hold off asking too many questions at once, but I have a long standing
issue that I'm really stumped on and could use some advice. I had a Varian
AutoX-style dual broadband probe recently break on my 400 (Protune box broke
a tuning rod, as it seemingly is programmed to do) and I fortunately I had
my backup probe (same type; autoX DB) recently repaired and ready to go.
Pulse calibrations were easy, but this backup probe hasn't been in the magnet
for a very long time and getting good shimming on it has been a huge struggle.
I've tried getting gradient shimming set up and no matter what sample I use
to make my shim maps, or how much manual shimming I do on beforehand I keep
ending up with my z5 shim going to the end of it's range and the resulting
gradient shimming doesn't work very well. I've seen this same issue on my
500 occasionally. Peaks are resolved but not very well and often there is
a shoulder near the very bottom of the peaks after grad shimming. With my
primary probe, I have the shims locked in and I get beautiful lineshape on
routine samples where I can resolve second order splitting often down to
baseline.
I've learned a lot about NMR hardware in the three years I've been managing
this facility but I think I was spoiled in grad school. Most of my graduate
career was spent with a modern Bruker instrument where 3D Topshim got me >95%
of where I needed to be and then it was just manual touch-up from there on
sample to sample. During the shutdowns in 2020 when I had no one using the
instruments, I dabbled with Varian's own 3D gradient shimming on my 500,
but with little success. I'm afraid I'm just not sure where to start in
Varian with a probe for which there is no previously existing set of shims or
even a decent map. Here is one of my attempts at mapping z1-5:
Link
https://drive.google.com/file/d/1-LppePDWZPvqnNufuhFBSzm3dFlGF20q/view?usp=drive_link
The protocols in Varian are not clear to me even with the manuals handy. I
understand in general that the lineshape sample (CDCl3 in Acetone) should be
used for the radial shims (since mostly my chemists use this instrument and
less so the bio folks), and then a more common solvent (CDCl3) for the axial
shims and routine shimming. I've even tried using the autotest sample for
mapping. But no matter what I do I always end up with z5 giving the "out-of-range"
warning.
I have tried reading several primers on the subject but it's like I'm just
feeling my way in the dark. Does anyone have a standardized way to shim a
probe from scratch? Also, Is there some other hardware issue that could be
causing this or am I just really, really bad at shimming?
Best,
David O
San Diego State University
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Received on Wed Oct 11 2023 - 13:52:19 MST