Dear Spinners
I have two ageing 300 MHz Bruker Avance MicroBay systems (AV-I) that
have served us rather well over twenty years and are still soldering on.
I don't see any $$ in the foreseeable future to replace them and so I have
to keep these as happy as I can. These systems are run using Topspin 2.1
PL10 and the software cannot be upgraded for this vintage of hardware.
They have developed the unique problem that Topshim for any of 2H based
solvent pretty much fails with the error codes of Raw Check: no signal at
all or Signal to Noise too low.
Even in the cases where the S/N of the lock signal is decent such as
that of DMSO or C6D6, Topshim says it has completed successfully, but the
improvement is by a factor of 1.0 i.e. nothing in the form of B0
homogeneity improvement is made.
The same system does fantastic when I shim on a H2O+D2O or
1H-Acetonitrile solvent i.e. when I use the 1H nucleus to generate the
gradient echo and do the shimming.
I have spent quite a bit of time following every possible lead (I have
taken one of the two systems offline for the past two weeks; the other
system is being used with touching up the shims by hand). Probeheads are
ruled out (different ones are tried) as are the basic hardware related to
the shims such as shim current boards and the shim stack. RX22 board can't
be blamed as well since the whole operation with 1H passes with flying
colors. RX22 is agnostic to the nuclei being pulsed since it does its
amplification at the Local Oscillator frequency of 22 MHz.
By sheer process of elimination, the only culprit I can think of is the
2H preamplifier slice. Here is where the reasoning becomes all the more
challenging. The likelihood of two systems failing exactly the same way
with two identical hardware components becomes rather low when we multiply
the individual probabilities. Nevertheless, the fact that these two
instruments are identical twins (with consecutive serial numbers !) and are
of the same age mitigates the 'unlikelihood' to an extent.
I am coming to you with my Hat in Hand and that is the motivation behind
this long winded story above. Do any of you have an HPPR/1 2H
preamplifier slice for a 300 MHz stashed away that you can donate or let me
borrow for testing my hypothesis i.e. 2H preamplifier failure is leading to
my poor/failed Topshim 2H performance ?
Thank you for sparing your precious time.
Best Regards as always
Rajan
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Rajan K Paranji, Ph.D.NMR Facility Manager
*Department of Chemistry**Room 65, Bagley Hall*
University of WashingtonSeattle, WA 98195
phone : 206 685 2581 fax: 206 685 8665email: rajanp_at_uw.edu
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Received on Fri Dec 09 2022 - 09:26:46 MST