Has anyone else run into the following issue on a Varian cold probe?
On our 800's cold probe, the 13C match appears to have drifted. We now
find the lowest match at what appears to be the limit of the 13C tune
range for both modereately salty samples and the doped water sample.
The C13 channel's performance seems normal otherwise with the same
90 pulse length even when slightly detuned to around 66-70 on the tune
meter. I am wondering if the preset match in the cold probes have a
tendency to drift (especially if the preset match is adjustable and
not a fixed circuit) over time with thermal cycling of the probe. Any
information on this behavior would be greatly appreciated.
Jack
ps We also have also observed a different artifact on the 13C channel
of our Varian 500 cold probe. On that probe, the minimum tune value
increased but the tune position didn't. I discovered that the 13C
channel could be brought back to previous lower tune value by inserting
a short segment of coax (so that channel seem to be sensitive to the
total length of cable). Our 800 cold probe's 13C channel isn't showing
that behavior. Inserting various lengths of coax doesn't change the
tune value (which isn't surprising since in this case the actual
tune stick position has changed.
--
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Jack W. Howarth, Ph.D. 231 Albert Sabin Way
NMR Facility Director Cincinnati, Ohio 45267-0524
Dept. of Molecular Genetics phone: (513) 558-4420
Univ. of Cincinnati College of Medicine fax: (513) 558-8474
Received on Thu Mar 05 2009 - 09:34:23 MST