Category Archives: problems&solutions

Should I wipe clean my NMR tube?

Dirt stains become little magnets once inserted into the big magnet and severely distorts the magnetic field homogeneity, and such distortions cannot be fixed by topshim or manual shimming. See the spectra below.

Red: Before wiping.

Blue: After wiping with KimWipe(r).

What to do if you have insufficient solvent

Normally, you should have 0.4-0.5ml of solvent, which is ca. 3-4cm tall in the NMR tube. If you have less than 3cm of sample, please follow these steps:

– instead of rsh, do rsh shims.short

– always lock after you do rsh

– You can try topshim, but watch if the lock line gets higher or lower after topshim. If it gets lower, topshim did not work, and you need to type rsh shims.short again to get back the better shim. Topshim does not always work for short samples.

– If topshim did not work, type bsmsdisp, and adjust z and z2 to get your lock level higher. z2 is the most important for short samples

– Shim is never perfect for short samples, so you need to be prepared to see low resolution on your spectrum. If every peak has the same tail, asymmetric lineshape, or fine splitting, it is mostly like a shimming problem.

“Sample Missing” and “lock” is not green?

Bruker NMR’s detect the presence of sample by trying to spin it.  If the sample cannot spin, then the bsmsdisp panel will show “sample missing”.  After you lock the sample, the lock button will not be green even though it actually has been locked and the scanning line has risen to the upper part of the lockdisp window.  You can still run your experiment in this situation.

Spinning improves the resolution of your spectrum to some extent.  However, the resolution without  sample spinning is usable in most applications.

Related link:  When it helps to spin and when not.

Typing “dir” cannot find my files…

Upon loading topspin, it will take a little time to load up the spectrum that you used last time. If you type dir when the screen is still blue, you will confuse topspin.

To solve the problem, go to File -> Open, and find the path that contains your data. It is usually /opt/topspin/data/[your login]/nmr. Open any data file. This will reset the default data file path to your own directory. If you type dir now, you will be able to see your directory.

If it seems to take quite long to load up the last data file once you start topspin, it is likely because you have too many data files. Delete some!