Hi Ken,
Is it possible that your C6D6 got contaminated with something? If you
acquire a 2H spectrum you can see what the lock is working with. To
do this, open a new dataset and read in the parameter set gradshim1d2h (this
will set the routing correctly.) Then set the pulse program to zg2h,
D1 to like 0.5s, TD to 32k and SI to 64k. If you've got a cryoprobe you
can tune the lock channel, otherwise you can't.
Once you've got the experiment set up, run it normally--lock, tune (if you
can), shim, and acquire with zg and process with the normal efp, etc.
That will show you the 2H spectrum that your lock is trying to work with.
It looks like your spurious signal might be like 3.5ppm away from the signal
you want to lock on, and naively I'd be a bit surprised if C6D6 didn't just
give you either a single peak or a reasonably narrow multiplet.
Anyway, in situations like this I always like to have a look at what the lock
is actually trying to lock on to make sure it looks reasonable.
One other detail--IIRC you just got some shiny new spectrometers, didn't you?
If so, there's an auto-phasing algorithm that might be able to help with this.
If you open edlock and look in the upper left there's a check box for "auto phase
during lock" and a pulldown menu. If that box is checked and "spectrum" is
selected in that menu then it's already enabled and you can ignore the rest of
this email.
If it's not set up and you want to use it, there are a couple of calibrations
that need to be done. If you want to do those, put a sucrose sample
(90% water, 10% D2O) in and lock on H2O+D2O. Then use ha and open the
BSMS service webpage. In there click service and log in. In the
username field put whatever you want (3 characters minimum) and the password
is 1964. Then go back to the main page. Click lock, and then I
believe lock control, and then field lock control. You'll see two buttons
in the lower section of the page--Auto phase calibration, and start H0 calibration.
Run both of those (click the button, and then wait until the routine finishes--
I think both take less than 5 minutes.)
After that open edlock in topspin and make sure the auto phase checkbox is
checked and that the pulldown menu shows spectrum.
This algorithm acquires a 2H spectrum in the background before locking, and
uses that to set the phase and make sure the peaks are in the right place
before it turns the lock on. It seems to work pretty well and if you've
got a solvent with multiple peaks it can do a nice job of getting the field
set correctly.
Cheers,Mike
On Wednesday, November 5, 2025 at 01:13:07 PM MST, Kenneth Sharp-Knott via groups.io wrote:
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.
- Why does this happen? I assume the referencing is set somehow
during the lock, so I guess it's locking on the wrong resonance?
- 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 - 09:02:09 MST