TopShim problem with old probe.

From: Bob Berno <bberno@mcmaster.ca>
Date: Thu Mar 19 2009 - 23:02:46 EDT

Hello fellow Bruker Users.

I was hoping that someone could help me to get TopShim to work on our 
recently upgraded AV500 system.

Here is a bit of the background:
We have an older, unshielded 11.7T magnet.  
The console and shim stack were recently upgraded from an old DRX system 
to a 2nd hand AVANCE system.  
We also upgraded the software from XWinNMR v2.6 on SGI to TopSpin v2.1 
PL3 on a Linux box.
The probe was not upgraded:  it is a 5mm BBIxyz-probe, and is 
approximately 9 years old, and does not have PICS.

This upgrade happened a few months ago.  While the system is performing 
wonderfully, we have thus far been unable to get TopShim (or 
2H-GRADSHIM) to work properly.

Here is what I've seen:
topshim 3d works fine on the sucrose standard.
topshim 1d does not work properly when shimming either 1H or 2H.  The 
problem is that the z-shim becomes mal-adjusted by a very large amount 
(over 1000 units). 

For example:

    * We start with 3D-topshim on sucrose standard,
    * Insert 1%CHCl3 in acetone-d6 (1H-lineshape standard) and observe
      :HUMP= 5/11Hz and FWHM = 0.67Hz.
    * Perform 2H-Topshim and record the 1H-NMR spectrum again.  The
      result resembles a deuterium powder pattern (HUMP is meaningless)
      with FWHM=45Hz.
    * Manually shim using ONLY Z-shim, and very quickly we are back to
      HUMP= 8/16Hz and FWHM = 0.67Hz.
    * We have observed a similar response from 2H-gradshim.


I know that there must be many of you out there who have an older probe 
and have recently upgraded to TopSpin.  
Have any of you encountered symptoms like the ones I describe?  
And more importantly, has anyone found a way of fixing the problem and 
making 1D TopShim work properly?

Thanks in advance.
Bob.

-- 
Dr. Bob Berno
Manager: McMaster NMR Facility
Department of Chemistry
McMaster University
1280 Main Street West
Hamilton, ON
L8S 4L9
(905) 525-9140 x24158 or x24686
Fax: (905) 522-2509
http://www.chemistry.mcmaster.ca/facilities/nmr/index.html

Received on Thu Mar 19 20:18:49 2009