i like this post (click again to cancel)
1
i dont like this post (click again to cancel) remove favorite mark from this question (click again to restore mark)

Why are some Dosy spectra 1d so distorted (like the one below)?. How can this be overcome?

distorted dosy spectrum

asked Jan 06 '11 at 18:59

%40's gravatar image

@
11

updated Jan 23 '11 at 17:12

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev
5571

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)


8 Answers:
i like this answer (click again to cancel)
1
i dont like this answer (click again to cancel)

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).

link

answered Jan 14 '11 at 04:07

bernie%20o%27hare's gravatar image

bernie o'hare
111

i like this answer (click again to cancel)
1
i dont like this answer (click again to cancel)

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

link

answered Jan 19 '11 at 19:59

Zhenshu%20Zhu's gravatar image

Zhenshu Zhu
21

i like this answer (click again to cancel)
1
i dont like this answer (click again to cancel)

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

link

answered Jan 25 '11 at 16:54

Pete%20Gierth's gravatar image

Pete Gierth
326

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 like this answer (click again to cancel)
1
i dont like this answer (click again to cancel)

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!

link

answered Jan 27 '11 at 17:56

Zhenshu%20Zhu's gravatar image

Zhenshu Zhu
21

i like this answer (click again to cancel)
0
i dont like this answer (click again to cancel)

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?

link

answered Jan 19 '11 at 17:25

%40's gravatar image

@
11

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)

i like this answer (click again to cancel)
0
i dont like this answer (click again to cancel)

oops That should read sine wave

link

answered Jan 19 '11 at 17:27

%40's gravatar image

@
11

i like this answer (click again to cancel)
0
i dont like this answer (click again to cancel)

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.

link

answered Jan 28 '11 at 11:12

bernie%20o%27hare's gravatar image

bernie o'hare
111

i like this answer (click again to cancel)
0
i dont like this answer (click again to cancel)

...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

link

answered Aug 11 '11 at 02:07

djh's gravatar image

djh
1

Your answer
Please start posting your answer anonymously - your answer will be saved within the current session and published after you log in or create a new account. Please try to give a good answer, for discussions, please use comments and please do remember to vote (login to vote)
toggle preview

powered by CNPROG