Hello everyone,
I have a question regarding gradient shimming with Topspin 3.5. I have a Fourier 300 system that is only able to use gradient shimming (tosphim will not work because of the design of the system). A while back gradient shimming was working fine and then suddenly the shims were not being pulled in properly. I would be able to manually shim the spectrum to come close to the specs, but once I execute 1D2H gradshim, all the peaks split and broaden. I am using two iteration steps: Step #1 highz4 window: 24, Step #2 midz window:20. I looked inside the probe and the quartz inserts are still intact and the NMR tubes are not warped or scratched. I tried remaking the shimmap following the standard protocol in "Gradient Shimming: Principles and Practical Aspects" manual from Bruker. I tried with a GdCl3.6H2O doped D2O sample and the sucrose standard sample because I read somewhere that using the lineshape sample as suggested in the manual for 1D2H setup is not good due to convection. Both gradient profiles look good and are not noisy. However, gradshim would still split/broaden the peak. I then decreased the window size to 20 and 15 respectively and gradshim appears to work properly; peaks are not split and line shape improved.
So my question is, what would typically be the cause for a need to change the window size in gradient shimming? Is there a gradient issue that I should be looking for? Preliminary tests with manual shimming saw all shims responsive, however there might have been one or two mid order off axis shims that required large changes (100+) to see some response (sorry don't recall which ones right now). Are there other hardware issues that could cause this problem?
Thanks,
Joel
------------------------------------------
Core Facility Manager - NMR,
Department of Chemistry
Johns Hopkins University
tel: 410-516-7456
nmr.chm.jhu.edu
Received on Mon Jun 06 2016 - 05:50:25 MST