Hi Ken,
That...is not a normal-looking 59Co spectrum. Temperature sensitivity is on
the order of 1.4-1.5 ppm/K (literature reports vary). Your spectrum is 2 ppm
wide so yours is a temperature gradient of 1.5 K (!?). That would certainly
explain why you're having problems with aqueous samples. As for why the
gradient is so high is another matter.
Geoff
________________________________
> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of Kenneth Sharp-Knott <kknott_at_vt.edu>
> Sent: Thursday, January 11, 2024 20:13
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [External] [AMMRL] Shimming issues related to oscillating lock level
Topline: Issue still not resolved - D20 samples unusable - CDCl3 looks normal
I'm now going to spam you with the information I've collected over the week
based on all of the excellent suggestions from the AMMRL users!
1. This doesn't seem to be an issue with shimming, but rather something =
impacting both the linewidth and chemical shifts of D2O samples in particular.
2. I cannot correct the lineshape manually. It is not correctable with tcorr.
3. Spinning vs Non-Spinning - Improved lineshape standard. Strange change to D2O sucrose sample. PDF attached
4. Menthol in CDCl3 lineshape is excellent
5. Possibly very very small chemical shift changes
6. Menthyl Anthranilate is DMSO is good
7. The probe coil temp is stable at 27
8. The VT gas flow is stable
9. The VT heater power is stable (no fluctuation beyond 0.1% heater power)
10. The VT sample temp is stable (no fluctuation beyond 0.1 Celsius)
11. Shim Coil Temp is stable at 300K
12. In order to eliminate the possibility of issue related to our house air,
I've tried using both our usual house air and boil off liquid high pressure N2 - no difference
13. Co59 samples chemical shift is stable for 10 minutes (every 10 seconds)
14. Co59 sample - there was some change in phase.
15. Room Temperature BBO probe does not exhibit any issues - shimming/lineshape is perfect across all solvents
16. Attached borescope of the probe shows there was some gunk on the sample cavity walls. I cleaned it - no change
17. After returning the Prodigy to the magnet (24 hour pump down) - no change
18. The lock level oscillation is observed with acetone - not D2O
19. The Prodigy platform is overdue for service (scheduled this month), but
there are no indications it is having trouble maintaining vacuum or dewar pressure.
I was pretty certain there was some kind of temperature gradient through the
sample, but the Co59 shift being rock solid has me doubting that. I'm pretty much at a total loss.
Sending it to the AMMRL team for more suggestions
Considering opening it up for organic solvent use until the engineer services the Prodigy platform.
--
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 Thu Jan 11 2024 - 13:00:28 MST