Dear Colleagues:
We have recently had the good fortune of installing two new Neo systems; a
400 and a 500 both with SampleCase's. As a result, I have said good-bye to
TS2.1.8 and am getting familiar with TS4.1.4. With this jump in TopSpin
comes a large jump and revamping of TopShim (1.2.2 --> 2.2.0). Because TopShim
looks quite different to me now in its reporting , Ive been watching it
perform and report on both of these walk-up systems with some regularity.
I have noticed on both of these new systems with RT probes (400 with a BBFO
iProbe and 500 with BBFO SmartProbe) that TopShim's behavior is usually as
follows:
* Iteration 1 is robust and results in a large improvement in homogeneity,
usually ending up with a FWHM somewhere around 0.4-0.5 Hz
* About 75-80% of the time, what follows is ~ 5 iterations where the
FWHM oscillates between ~ 0.3 and 0.9 Hz, resulting in the message "slow
convergence detected, shimming aborted. Using the best result as the final
shim state". When I look at the maps, it appears that in the final 5-6 iterations
TopShim is trying to deal with the effects out at the edges and is unable
to do so reliably.
* I have noticed on both of these systems that z8 does not reliably
converge but instead oscillates +/- 2000 units, on consecutive TopShim runs
on the same sample. This is despite both of these systems having a BOSSIII
shim system where ordmax=8 is supposed to be used according to documentation.
* This behavior is independent of the TopShim observe nucleus (1H/2H).
I am considering using the "fastfine" option on walk-up samples but what I'd
really love to know is how I might tweak TopShim such that the above behavior
is the exception rather than the rule. Is this a matter of using the zrange
option to avoid the edges and thus shrink the region over which flattening is
performed but where the hump is still tolerable?
Id love to hear the group's thoughts on this topic. I should be clear that
the results we are obtaining from these two systems are absolutely fantastic!
This email is just about me (possibly down a rabbit hole) wondering if
with a deeper understanding even more can be gained.
Thanks!
Mike
Michael D. Lumsden
Nuclear Magnetic Resonance Research Resource
Department of Chemistry, Dalhousie University
6274 Coburg Road
P.O. Box 15000
Halifax, Nova Scotia, Canada
B3H 4R2
Phone: 902-494-1635
FAX: 902-494-1310
Web: http://www.dal.ca/diff/nmr3.html
Received on Wed Feb 15 2023 - 09:26:58 MST