[azmanam]

We're using a Bruker NMR (300 and 400 MHz).

I know you're not supposed to leave the lock on after you take your sample out and leave, but what is the reasoning behind that?  Does it have something to do with the instrument trying to lock on a solvent that's not there?  And when the next person wants to take an NMR, if it's not the same solvent they'll load shim files for a different solvent - while the instrument is still trying to lock on the previous solvent?

Thanks,
-AA

[agrobert]

I think it is so the calibration does not drift.  Although you always relock and shim, it is a reference point that lets others know the machine is working properly.