DOSY deep signal distortions

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Hi heveryone, I'm trying to run some DOSY experiments, but the resulting spectra are VERY distorted, and this is not just a problem of phase. The strange thing is that these distortions didn't appear as long as a few days ago... Have you got any suggestion? Further details: The spectrometer is a Bruker 400MHz, and the sequence is the dstegp3s

dosy

asked Jun 25 '13 at 08:57

Ruggero
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Usually the answer is lock phase being set incorrectly.

See

http://qa.nmrwiki.org/question/216/distorted-dosy-id

for an extreme example of distortions probably caused by the lock phase being set wrongly. If it's not so far off, usually you just see a dip on one side of the peaks.

The lock phase is changed by a number of things, including the tuning of the x-channel of broadband probes. The command "autophase" will adjust the lock phase - run this immediately before acquisition of the DOSY data so that nothing changes between adjusting the lock phase and acquiring the DOSY.

Does that help?

link

answered Jun 25 '13 at 17:12

Pete Gierth
401

Dear Pete, thank you for answering my question! Actually, I hit the autophase command every time before DOSY data acquisition... Do you know if there is some other adjustments do do? Could it be that the autophase command was not able do adjust properly the phase? Thank you again! - Ruggero (Jun 26 '13 at 00:51)

It's possible that it didn't get the right answer, but usually it's close - could try changing the lock phase manually by eg +/-5 deg,rerun and see if that's better. Also you can run unlocked - use command "lock_off" which will turn off the lock and stop it turning back on during the experiment. - Pete Gierth (Jun 26 '13 at 12:58)

Note that after running unlocked, you should open a normal proton experiment and run the command "ii", then lock again. The "ii" forces the preamp back into lock mode, otherwise it won't lock! - Pete Gierth (Jun 26 '13 at 13:00)

Again, thank you very much for these precious advices. I will give it a try! - Ruggero (Jun 26 '13 at 23:02)

...Or maybe a hardware problem of the lock system? Or the gradient system? Do you have access to gradient shimming?
Getting a field profile would help diagnose a gradient coil problem I think.
We had a problem with an instrument that would incorrectly enter 'lock-hold' during a gradient experiment, giving distorted lines in phase sensitive, non-magnitude experiments. We diagnosed the problem after I disconnected the 2H lead during the experiment...

Duncan

link

answered Jun 26 '13 at 03:30

djh
1

updated Jun 26 '13 at 03:31

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Asked: Jun 25 '13 at 08:57

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Last updated: Jun 26 '13 at 23:02

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