Why are some Dosy spectra 1d so distorted (like the one below)?. How can this be overcome? asked Jan 06 '11 at 18:59 @ |
Dosy is very sensitive to magnetic field disturbances. Make sure no one is walking near the magnet (keep everyone out of the 2G line). More importantly make sure there are no moving metal objects causing field perturbations during the experiment (i.e. a swinging lab door that looks wooden but actually has a metal frame under the wooden laminate). answered Jan 14 '11 at 04:07 bernie o'hare |
Good quenstion! There are lots of attempts to solve the distortion problem. recently, a publication on JMR: a 45 degree pulse instead of 90 degree was used to cancel the antiphase signal. See here: J-modulation effects in DOSY experiments and their suppression: The Oneshot45 experiment Original Research Article In Press, Corrected Proof, Available online 21 November 2010 Adolfo Botana, Juan A. Aguilar, Mathias Nilsson, Gareth A. Morris answered Jan 19 '11 at 19:59 Zhenshu Zhu |
Given the spectrum you posted, I think this is more than just antiphase components - this looks like effects of significant field disturbance. It's possible that the lock settings are not good - try the command "loopadj" before acquiring the spectrum. This will adjust the phase of the lock signal (if this is far off, then the lock can have problems recovering after the gradient pulses of the diffusion experiment, which can result in spectra like yours), and optimise the lock regulation parameters based on the strength of the lock signal. You should check the lock phase after loopadj and compare with the value in edlock for that solvent. If it is a long way off, it's probably worth updating the default phase in the lock table (talk to the system administrator about this). Pete answered Jan 25 '11 at 16:54 Pete Gierth Dear Pete, I believe you are right. The antiphase problem won't be like this. - Zhenshu Zhu (Jan 27 '11 at 17:50) I've run lots of diffusion measurements (Avance III 500) and have never seen anything like this. Occasionally I'll ge a tiny (maybe 1-2% ?) bit of distortion at the base of very sharp peaks. I agree with Peter that you should check field stability and lock settings first, and then the other parms. - Kirk Marat (Feb 02 '11 at 08:59) |
I have another suggestion, using "ased" and check the value of gradient field eg. GPZXX. And try suggestion value provided by Bruker. Improper setting of gradient will also make the spectrum like this. Good luck! answered Jan 27 '11 at 17:56 Zhenshu Zhu |
I dont have enough carma points to attach the spectrum. Imagine a sne wave going through an out of phase peak....on every peak. Posting comments does not seem to work either? answered Jan 19 '11 at 17:25 @ Just upvoted your question, with 11 points you should be able to upload an image. Also it should be possible to edit posts. Do you see any error messages? I already have upgraded version of the software, will try to migrate in two weeks. Thanks for your patience. - Evgeny Fadeev (Jan 19 '11 at 17:40) |
If using a Bruker spectrometer try using the ledbpgp2s1d and ledbpgp2s pulse programs rather than the more conventional stebpgp2s1d, etc... experiments. The previous are the same stimulated echo sequences but include a longitudinal eddy current delay, which when not taken into account may cause some distortion. answered Jan 28 '11 at 11:12 bernie o'hare |
...I've seen a similar thing I think a few years ago, due to a hardware fault. It only came to light doing 1d gradient experiments; the 2d ones the instrument did were all routine magnitude ones. There was a dodgy wire that caused the instrument to incorrectly enter the 'lock-hold' state during gradient experiments. Took a while to track down, we had the clue after I disconnected the 2H line during the experiment and the problem went away. Duncan Dept. Chemistry University of Cambridge answered Aug 11 '11 at 02:07 djh |
Hello, I am running Dosy experiment using ledbpgp2s sequence. I am getting sort of signal distortions as same as the figure above. I tried the solutions you have mentioned in your discussions. I couldn't execute the loopadj as it always says lock gain is too high. I try to change the lock gain manually but still it couldn't keep that value. Finally, i performed Dosy with out lock on. I did lock off,locnuc off and l12 = 0 and run the experiment again but the problem still persists. I tried with other wide bore spectrometer and I don't get the distortion. The problem remains only in the Cryoprobe standard bore spectrometer with icon nmr. I am not sure what to try out more ! Please input your thoughts. Regards Uma answered Mar 30 '15 at 00:08 |
Could you describe the distortions and post a picture? There is button in the toolbar that allows to upload an image. - Evgeny Fadeev (Jan 06 '11 at 19:52)
I've merged your follow up picture post into the original question - the posts are editable, so that they can be improved - Evgeny Fadeev (Jan 23 '11 at 17:14)