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 shims.best, 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.