Greetings All,
I am having a very unusual problem with spectra collected above ambient
temperature obtained on a Varian INOVA spectrometer. It seems that when I
collect spectra at almost any temperature above 25 deg C, the peaks
broaden and acquire distorted lineshapes. This is on small molecules
(nucleosides) that I have looked at before on a Bruker spectrometer where
the already sharp peaks get sharper and more resolved as the temperature
is raised through 80 deg C. Shimming seems to be fine and the lock level
also increases with the temp. and the appropriate shims adjust
accordingly. Discussions with others have suggested a tempertaure gradient
through the length of the sample and accordingly, adjustments were made to
the LPM flow of the probe body and VT gases to no avail. It is not
specific to the probe since it occurs on different probes (both Nalorac
and varian types). I also played with the "VTC" command and that is
also not the problem. The resonances should sharpen at higher temps but no
matter how hard I shim, no go. Anyone experience this? I'm somewhat at a
loss and any suggestions would be most appreciated.
Thanks and Happy Turkey Day,
Joe
Joseph J. Barchi, Jr.
NMR Facility Head
NCI Frederick
Bldg 376, Rm 209
376 Boyles Street
Frederick, MD 21702
301-846-5905 (voice)
301-846-5920 (lab)
301-846-6033 (FAX)
barchi_at_helix.nih.gov
Received on Mon Nov 26 2001 - 09:19:38 MST