AMMRLers,
I have been seeing a pretty weird problem on my 500. Sometimes when I
swap probes, the shim goes to (really bad). As in linewidths of (many)
10s of Hz. But only sometimes.
The most recent example is that last week the 5 m probe was in and
shimmed pretty well. Swapped it for the 2.5 on friday and all was
well. Swapped the 5 back in on Monday and again, all was well. I did a
little shimming on Monday and saved the file. Tues. I swapped the 2.5
back in. The lineshape was terrible, the field had to be changed to get
the system to lock, and the o1 necessary to put water on resonance was
off by about 1100 Hz. Today I put the 5 back in, read in Monday's shims-
and the field was fine, but the shims... not so good.
Last month, this happened about every probe swap. I looked up the bore
and didn't see anything. I cleaned the bore anyway, and the problem
seemed to go away - until yesterday. When this first started, I blamed
the surrounding- esp. as it seemed that the nearby (touching 5 gauss
lines) 250 also seemed to be changing. Now, I don't think so. I can't
find any changes in the nearby labs- and the shims are fine as long as a
probe is left in the magnet. I am sure the probes are aligned the same
every time- I have marks on the probe and magnet.
Last month, z4 was the big changer. Today, z4 was not too bad, but
lower x,y,z all needed some adjustment.
Ideas, thoughts, suggestions??? Please note that not-swapping probes is
not an option.
kas
--
Karen Ann Smith karenann_at_unm.edu
Director, NMR Facility Adj. Asst. Prof.
Dept. of Chemistry Clark Hall
University of New Mexico Albuquerque, NM 87131
505.277.4031 url: http://www.unm.edu/~karenann
Out of this world screensaver: http://setiathome.ssl.berkeley.edu/
"There is nothing a good day of cycling won't cure."
Received on Wed Apr 10 2002 - 16:38:49 MST