We have been having a problem for a while and, especially now when we
are trying to apply chemometrics methods to 2D NMR data, it is
becoming a real issue.
It has to do with contour peak phases in 2D HSQC spectra.
It seems we can never phase every peak in the spectrum -- if you
phase some, others are necessarily out of phase in a distinctly non-
linear way, particularly the intense contours.
This is NOT an issue with a single spectrometer -- it is something to
do either with the types of sample and/or the parameters, and/or ??
The same "problems" are on 500-750 cryo machines in two countries
(and also on non-cryo at 360 MHz). We're using the ea si hsqc expt
(Bruker standard -- sorry, forgot the new name for a bit, but used to
be invietgpsi).
The samples have a range of component intensities, are fast relaxing
(proton fid is dead in about 100 ms). We have tried the obvious
things (is relaxation delay too short -- no, 1s for something that
relaxes in 100 ms, AQ is 200 ms), turing p28 off or not, and various
other things. But we have not yet tried the Adiabatic variants that
may help if it is a J-mismatch problem (with 180s).
Anyone know how we might be able to solve this? (after acquisition
(by processing) would be great (e.g. is it that the early part of the
FID is messed up, but with digital we don't know how to manipulate
that the way we could in the old days), but before would also help
tremendously for the future). Any suggestions? Does anyone need to
see a dataset?
Cheers and thanks in anticipation.
John
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John Ralph
US Dairy Forage Research Center, USDA-ARS and Dept. of
Biological Systems Engineering
1925 Linden Drive West Univ. of
Wisconsin, Madison
Madison, WI 53706-1108
(608) 890-0071 FAX (608) 890-0076
E-mail: jralph_at_wisc.edu
http://www.dfrc.ars.usda.gov
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Full-text Publications available directly from:
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Received on Fri Nov 24 2006 - 08:26:10 MST