Hello folks,
I am working on a gradient shimming problem without any success and perhaps someone out there can provide me suggestions or hints to resolve it. The machine is a Varian MercuryPlus (6 years old) console working at 300 MHz. The Z gradient is generated with an homospoil pulse.
The gradient shimming (with gmapsys, autoshim on Z, or with the chempack automation) routine works ok, the rms error is minimized and converged, but the proton spectrum shows splittings. I discovered a broken glass insert, I then pulled out the probe and installed a backup one, manually shim it until a reasonable lineshape was obtained, redo a shimmap and autoshim on Z. The result was not perfect but workable. When I record spectra on other samples/solvent, the autoshim finishes ok, but again signals show splitting related to bad shimming, since I can manually adjust Z1 and Z2 and remove those splittings.
I then tried to record a fresh shimmap - no change
I re-positionned the probe in the magnet - rerun a shimmap - no change
I modified some parameters such as the echo delay (d3) or the window size (gzwin) - again no success
The shimmap looks fine (on Z1-Z4, correct shape for each shim)...
I noticed that when the sample rotation is stopped the lock signal drops by 40%. Can it be related ?
I am running out of ideas. Any suggestions will be greatly appreciated.
Cheers
Pierre
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Pierre Audet
Département de chimie
Pavillon Alexandre-Vachon
1045 Avenue de la Médecine
Université Laval (Québec)
CANADA G1V 0A6
Tél: (418) 656-2131 x4296
Fax: (418) 656-7916
Received on Wed Mar 17 2010 - 03:58:56 MST