*Topline: Bruker was right from the beginning. The issue was a problem
with the VT gas flow stemming from a malfunction in the BVT3000.*
After replacing every inch of tubing to the console and from the VT unit to
the probe trying to find a leak, blockage or kink, I noticed that the float
ball in my BVT 3000 did not drop when it was turned off. Fortunately, I
have lots of old instruments with BVT3000's and swapped them out.
Turns out the old unit was obstructing the flow in some way. The flow did
increase/decrease, but was evidently less than 100%. I was unable to tell
a significant difference but clearly, there was one. First clue after
replacement was that the power required to regulate at 25C went from 1.1%
to 0.5%.
After replacing the BVT 3000 and redoing 3D shims I was able to get
excellent lineshape and my D2O samples look excellent. As to the Co59
sample, it still looks a little misshapen, but I'm getting 50Hz instead of
3-4ppm. Not perfect, but likely better than it's been in a long time.
I should have probably caught this sooner, but the BVT3000 seemed to be
regulating the flow.
On another note, I think it would be nice to get a flow meter from these
kinds of flow rates. Any suggestions? The only ones I have found are for
much lower flow rates.
Thank you all for eventually getting me pointed in the right direction.
I've learned a ton about VT, temperature gradients, convection, Co59 and
many other things that I will employ in the future!
--
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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Received on Fri Jan 12 2024 - 10:48:39 MST