Joe,
Yesterday, when we were analyzing NMR spectra, I kept dodging the technical
errors in those measured data (“for reasons I won’t go into”).
Here’s an NMR users guide that goes back to the 1990s on the subject of
‘NMR magnet shimming’: or the ‘Art’ of removing inhomogeneities
in the magnetic field within the region where the sample solution sits. In a
mathematical terms, the state of homogeneity is a chief when all magnetic field
vectors become uniform: pointing in the same direction (parallel) and the same
magnitude. It is an absolute requirement for a high quality NMR spectrum!
‘In the old days’, shimming had to be done manually - literally
turning some or all of about a dozen dials (so called axial shims, Z0, Z1, Z3, etc.
and transverse shims X, Y, X**2…. X**2-Y**2! )that alter the DC current
to ‘shim coils’ - until the ‘signal’ (a deuterium resonance)
was maximized. On most modern instruments, shimming is done automatically, but
apparently even now in PacHall, an inattentive operator can screw it up. Worse,
the don’t even notice!
- Ted Molinski
On Oct 11, 2023, at 10:17 AM, Mark Swanson <mark94131_at_gmail.com> wrote:
Hi David,
I've often found this article to be helpful. They go through a manual procedure
starting on page 13.
Cheers,
Mark
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Received on Wed Oct 11 2023 - 11:57:17 MST