Hello everyone,
We have a Varian 400 Mercury here, and we've been using homospoil auto shimming on H2 for both our 5mm id/pfg and 10mm BB probes. In the past, we usually update our shimfile/shimmaps every 6-8 months, and everything works pretty good--shimming usually converge after 2 iterations, sometimes 3. Last Monday, however, we started to have trouble with autoshimming on both probes. The symptoms were the same--Z5 constantly went out-of-range, and when we turn off Z5 shim, it took 4 or 5 iterations to converge and on the resultant spectra, there was always a broad base. Both shimmaps on these 2 probes were updated in Feb. Here is what I've done in trying to trouble shoot--
(1) checked find z0: autofind z0 value is pretty close to manually found z0, difference is within 5 units;
(2) checked lock channel: locked a sample and let it sit for 2-3 hrs, the lock level was stable;
(3) checked and cleaned out the upper stack.
(3) in an attempt to update the shimfile (probename_hs_d2o), I manually shimmed with the H1 lineshape sample (CHCl3 in Acetone-d6) on all 14 shimming channels. All shims were responsive--Iock level goes up and down when changing the shims, but I was not able to shim this sample into spec. (0.45/6/12 at 50%/.55%/.11% peak heights). The res. numbers I typically got was ~.3/8-15/15-20. So there is always a broadbase on the lineshape peak. I shimmed the higher order axial and non-axial shims quite extensively. No spinning side bands were observed, but the broadbase was always there. In the past, I never had much trouble shimming this sample into spec.
When shimmed on the doped 4 Hz water sample, I was able to get 3/56/86, and make a decent shimmap with gzsize=4. When ran autoshimming using this new shimmap, the same problem occurs--it takes >3 iterations to converge, and the lineshape is not good--either broadbase on bottom of peaks and/or broad peak in general.
I wonder if anyone from AMMRL has experienced a similar problem. Just to let you know, I am an organic/polymer chemist with no formal training in NMR spectroscopy, so I am learning to take care of this instrument. Any help would be much appreciated!
Tracy Zhang, Ph.D.
Analytical Chemist
GE Advanced Materials
Building 1, 1 Lexan Lane, Mt. Vernon, IN 47620
Phone: 812 831-4651, DC: 8*393-4651, Fax: 812 831-4917
tracy.zhang_at_ge.com
Received on Wed Apr 06 2005 - 18:43:51 MST