Hi Ken,
I know of two different circumstances that confuse things with lock, multiple
deuterium signals and field drift.
Accidental contamination, intentional mixture, and exchangeable nuclei can
all introduce multiple deuterium resonances. It can force the software to
"guess" when it searches for a lock signal and sometimes it chooses wrong. A
quick 2H spectrum would tell you if that's a concern for this sample. You
can fix it by locking manually and making sure to choose the "correct" signal
for reference purposes. If that solvent matrix is a recurring customer then
it's worth adding it to the prosol table as a new solvent choice, which
should mitigate the problem going forward and make more agreeable with
ICON.
AFAIK lock scan searches a fixed frequency window calculated from the set
spectrometer frequency. Field drift eventually moves resonant frequencies to
the window's edge and beyond. Since main field typically drifts downwards
I would've predicted it affecting more shielded nuclei like acetone or methanol
before benzene. If it's been months/years since the last main field calibration
then it's probably worth an update. Also true of recently charged magnets
where the field is still settling. iirc there's some sort of sideband (unsure
of the correct vocab) that can appear in lock scan. If the software assigns
it as the major signal then it could cause the same problem, and should
similarly clear up by recalibrating the main field.
Scary thought, if it is a main field problem, and if it's not clear why that
might have happened...I'd recommend a drift test. Sudden field changes
affecting lock is a canary-in-the-coal-mine for magnet health.
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of Kenneth Sharp-Knott via groups.io
> Sent: Wednesday, November 5, 2025 3:12 PM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] Incorrectly refereced C6D6
Forgive me, I feel like this is something I should know....
I've been working with a C6D6 sample today and about ½ the time it's
completely incorrectly referenced to the point that ½ of it is off the
scale. The samples are run on Bruker in ICON, yes, I'm selecting the correct
solvent... 🙂 Unfortunately, sometimes it happens during an HSQC
and it gets clipped due to the au program setting the sweep width.
1.
Why does this happen? I assume the referencing is set somehow during the lock,
so I guess it's locking on the wrong resonance?
2.
How can I prevent this?
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 Nov 06 2025 - 07:51:56 MST