RE: Resonance distortions when using wet for solvent suppression

From: Rich Shoemaker <rshoe_at_wwitch.unl.edu>
Date: Thu, 7 Sep 2000 13:09:39 -0500

If indeed these distortions are due to an instability in the field-frequency
lock, it might also help if (after optimizing the lock power and phase) to
lower the lock gain by ~50%. I don't have a Varian Inova, but there is a
well-known phenomenon often called "lock-push/pull", in which an over-driven lock
circuit causes a periodic instability/drift in the field (the lock
pushes/pulls the field about the center value). If the lock phase is also
off, this instability would be asymmetric about the center field.

I have seen artifacts caused by an over-driven lock on many kinds of
instruments (often misinterpreted as spinning sidebands, or a consequence of
floor vibrations), and the problem vanishes if I lower the lock gain. So, I
shim with the lock gain up (for maximum visual dynamic range for shimming),
and then lower the lock gain prior to acquisition.

This may or may not be related to your problem, but it might help.

Rich Shoemaker

----
Richard Shoemaker, Ph.D.                        	Phone--(402) 472-6255
Instrumentation Director, Chemistry             	FAX---- 		  -6964
Research Associate Professor, Chemistry
University of Nebraska-Lincoln
URL:  http://www.chem.unl.edu/nmrlab.html
-----Original Message-----
> From:	Mark.Dixon_at_astrazeneca.com [mailto:Mark.Dixon_at_astrazeneca.com]
> Sent:	Thursday, September 07, 2000 3:53 AM
> To:	ammrl_at_wwitch.unl.edu
> Subject:	RE: Resonance distortions when using wet for solvent suppression
Dear David,
I too have seen these distortions.
Advice given by the Darmstadt Apps. lab. seemed to work for me, namely
maximise your lockphase in the acqi window ( whilst locked on ).
The artifacts are then minimised at the very least, sometimes they go away
completely !  ;-)
Mark Dixon
AstraZeneca R&D Charnwood,
Loughborough, UK.
> ----------
> From: 	David Grace[SMTP:DG_at_NYCOMED.COM]
> Sent: 	Wednesday, September 06, 2000 3:31:33 PM
> To: 	ammrl_at_wwitch.unl.edu
> Subject: 	Resonance distortions when using wet for solvent suppression
> Auto forwarded by a Rule
>
Hello everyone.
We have been using the wet solvent suppression sequence for suppressing the
water resonance in 1D proton spectra. When we do this on our pfg id probe on
the Varian Inova 500 we observe a distortion on resonances removed from the
suppression point. The distortion is most noticeable on sharp intense
singlets. Such a distorted singlet seems unusually sharp on one side and has
a marked negative spike, whilst the other side is normal or maybe somewhat
broadened. Its like I've applied resolution enhancement to one side of the
resonance and line-broadening to the other side! The effect is present even
using only one transient and no steady state pulses.
Has anyone seen this and if so an explanation? It would also be nice with a
solution as well!
best wishes,
David Grace
Nycomed Amersham
Manger NMR group, Oslo, Norway
voice +47 23185006
fax+47 23186014

Received on Thu Sep 07 2000 - 13:24:39 MST