Date: Mon, 8 Jan 2024 12:38:19 -0500
There appears to be more at work here than originally thought...
I believe this all started after a routine refill of the Prodigy N2 dewar.
Shims are terrible. Far worse in D2O with very broad lines. The
Lineshape standard will sometimes meet specs, but samples in D2O are consistently
bad. This is both with topshim and after attempting to manually correct the shims.
I have 3D shimmed repeatedly. This system, an Avance II 500MHz, generally
needs convection compensation. My usual topshim sequence has been
'topshim convcomp ordmax=6 tuneaz'.
The Bruker engineer took a look remotely and didn't find evidence of a dirty
probe or cracked insert. He suggests the issues are related to an oscillating
lock level and blames the oscillation on convection. He suggested a blockage in
the VT gas. I have traced the line and there is no blockage, kink or break
in the line. I have removed the line and can feel VT gas flow which in
increases and decreases normally with the VT Gas Flow setting.
By lock oscillation, I mean that the lock level will be steady and then
increase or decrease 5-10% over a maybe 20 seconds and then stabilize.
This happens repeatedly to varying degrees.
Does anyone have any suggestions for a cause for this lock oscillation?
30mg Sucrose in D2O - red is usual - blue is current state.
Lineshape Std 0.3% Chloroform in Acetone
Ken Sharp-Knott
Manager of Analytical Services and the NMR Facility
Department of Chemistry
Virginia Tech
(540)267-6502 (Cell)
(540)231-0885 (Office)
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