Hi all,
Thanks to all who responded to my question about water suppression. You all point out that the reason is radiation damping of water.
I find the watergate methods is better than gradient coherence selected methods, and the excitation sculpting also give good result.
Here is the summary.
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You probably experience radiation damping with your high Q probe. There
is a paper from Hoult taking about it.
Good luck, CJ
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Most likely it is caused by radiation dumping of H2O since cryoprobe has
very high Q.
Watergate or any other gradient type water suppression shall do better job.
Good luck,
Xiaogang Han, Ph.D.
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You ought to be able to shim much better than that. Are the 13C lines
also broad? If not, you might have radiation damping. Try the zg
experiment with a small tip angle ~5 degrees and with a 90. If the
FWHM is much larger with the 90 you have radiation damping. If not,
you have other problems.
Good Luck!
Jeff
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is this water line width with or without water suppression.
Without water suppression it is quite normal for water to have a much
larger linewidth due to the increased radiation damping. Cryoporbes have
a very high Q and therefore the radiation damping is quite a bit higher
than on conventional probes.
The quality of water suppression will depend a lot on the type of
sequence you use for your triple resonance experiments.
You can usually acheive excellent suppression by using watergate type
suyppression. Examples of such sequences are hncogpwg3d or hncagpwg3d.
You want to look for "wg" in the sequence name.
Echo Antiecho gradient coherence selected experiments also give good
watersuppression. With cryoprobes it is often advisable to try with or
without trim pulses before the first INEPT transfer or flip back pulses.
Best Regards
Clemens Anklin
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in my experience, excitation sculpting is extremely versatile
and produces excellent-quality spectra; read
T.L. Hwang, A.J. Shaka,
Water suppression that works - excitation sculpting using arbitrary wave-forms and pulsed-field gradients,
J. Magn. Reson. A 112 (1995) 275-279.
Put water on-resonance and try it with a Gaussian soft pulse,
repeating the G - S - G block twice with gradient pairs
being either unequal or applied along different axes.
Optimize the soft-pulse power for the best water suppression.
If the water peak is too broad, simply shorten the soft pulse
(0.5 or 1 ms) until water is fully suppressed.
Good luck,
Konstantin
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