Hi David,
I've often found this article to be helpful. They go through a manual
procedure starting on page 13.
Cheers,
Mark
On Tue, Oct 10, 2023 at 6:03 PM <daveonofrei_at_msn.com> wrote:
> 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 - 10:17:20 MST