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Hello,

I am running Dosy experiment using ledbpgp2s sequence. I am getting sort of signal distortions. 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

asked Mar 30 '15 at 22:03

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Umayal Rakesh
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updated Mar 30 '15 at 22:04


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Hi,

Can you post a picture of the first row of the spectrum?

If you can't run loopadj, just run autophase (this is the important bit of what loopadj does). Loopadj runs autogain because it is using the value of the lock gain after autogain as a measure of the signal:noise ratio of the lock signal.

Presumably since you have a very high lock gain you are using CDCl3 solvent? In which case in the cryoprobe you will also have serious convection issues. You can reduce the effect of convection by putting your sample in a 3mm tube, or you can use the convection compensated sequence dstebpgp3s.

Pete

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answered Apr 05 '15 at 08:37

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Pete Gierth
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Hi,

Thank you for the answer. I couldn't able to post the picture here. It is something like, the spectrum has dips at one side of each signal. yes, I am using CDCl3 as solvent. But I have also tried with just D2O (to check J modulation effects to have caused this problem) and the same distortions were there.

Regards Uma

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answered Apr 16 '15 at 02:08

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Umayal Rakesh
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Is it maybe a processing problem? Or maybe a shimming problem? I wish you could give more information about your sample. Type of compound(s) , concentration, temperature at which you are doing your experiment, how your 1D looks (do you have the same distorsions in a normal 1D, or in a 1D dosy?)...

Not being able to post images is quite awful...I hate these kinds of rules in this type of forum. Try to upload your image on an image hosting website and then posting links here. I'm not certain this will work, you might not be able to post links.

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answered Apr 23 '15 at 02:27

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updated Apr 23 '15 at 12:02

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Thank you Gravatar for the reply. The same problem persists even with the 1D dosy. I tried the same experiment on same sample, same solvent with a QNP probe on WB magnet and I dont see any signal distortion. The distortion is similar to the one asked earlier in this forum. Here is the link, http://qa.nmrwiki.org/question/216/distorted-dosy-id

I doubt more than a sample or pulse sequence problem, the distortion may have occured due to instrumental effects (occurs only with Cryoprobe, SB magnet so far), or locking or shimming misadjustments.

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answered Jun 01 '15 at 20:26

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Umayal Rakesh
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I'm guessing you parametrized your dosy correctly? (D20 and P30 in Bruker systems) Otherwise, it's possible it's a convection problem as suggested by Pete. Other than using the 3mm tubes,I would recommend using convcomp when you're running topshim. Also if possible try switching your solvent(CDCl3 has a particular convection problem).

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answered Jun 08 '15 at 03:44

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