Atilano,
Addendum: I assumed your air supply is stable. All bets are off if spectral
line movement is due to a compressor cutting on and off, or a drier
cycling, for example. There are solutions to such problems (some relatively
simple), but you'll have to do something about it if it turns out to be the
issue.
Inspecting a stacked plot of successive single or small-count runs will
characterize the situation.
Gerry
On Sat, Jun 13, 2015 at 12:42 PM, Gerry Chingas <gerrychingas_at_boisestate.edu
> wrote:
> I second Huaping Mo's suggestion. In fact, the temperature calibration
> procedure for Bruker's VT unit relies precisely upon the temperature
> sensitivity of spectral lines of the calibration standards. (You might want
> to check out the procedure documentation to see how it relates to your
> issue, and to find some starting references). In general, even within a
> single compound, the temperature sensitivity of individual lines will have
> differing degrees of temperature sensitivity. You can try running your
> sample with VT on, waiting a few minutes each time for stabilization, to
> see if that fixes the problem; or, if you really want to know more
> decisively, you can take a couple of runs at temperatures 5 or 10 C apart
> to see how big the temperature sensitivity is in Hz/C. (Keep in mind you're
> measuring the spectral shift of your sample relative to the lock line.)
>
> This is an example of those "well-known" phenomena that have been known so
> long they're often forgotten, notwithstanding a vast history in the
> literature.
>
> Regards - Gerry
>
>
>
> On Mon, Jun 8, 2015 at 7:34 AM, Huaping Mo <hmo_at_purdue.edu> wrote:
>
>> Dear Atilano,
>>
>> We recently dealt with a very similar issue as yours. While we are in the
>> process of putting together some theoretical analysis and solutions, based
>> on the symptoms you described, I believe a very likely cause is the
>> temperature fluctuation within the sample, either due to ambient
>> temperature change or VT temp control. You may find on some days the
>> spectrum looks perfectly fine and on other days it does not look as good.
>>
>> Best regards,
>>
>> Huaping Mo, Ph. D
>> Purdue University
>>
>> ----- Original Message -----
>> From: "Atilano Gutiérrez Carrillo" <agrmn_at_xanum.uam.mx>
>> To: ammrl_at_ammrl.org
>> Cc: "Atilano Gutiérrez" <atilanonmr_at_gmail.com>
>> Sent: Friday, June 5, 2015 2:15:46 PM
>> Subject: AMMRL: LOCK STABILITY PROBLEM / DILUTED D2O SAMPLES
>>
>>
>>
>>
>> I have the following problem:
>>
>> I have a dilute solution of an organic solid sample solved in D2O, that
>> requires at least 512 scans in order to have a good 1H spectra with an
>> acceptable S/N ratio. Acquisition takes more than an hour. However, D-lock
>> is not enough stable along the acquisition time. Signals asymmetrically
>> broadens as acquisition proceeds. For instance, the 0.00 ppm TSP methyl’s
>> signal, at the end of the acquisition could be as broad as 2 to 3 Hz with
>> more than one maximum. It seems that signals shift up field at every single
>> scan. It is worth to mention that field homogeneity is good. If acquisition
>> is halted at any time and a single scan spectrum is acquired, the 0.00 ppm
>> signal lineshape is almost perfect (0.7 Hz wide at HHFW) . Thought ,its
>> chemical shift would have changed by some hundredths of Hz.
>>
>> Acquisition is taken place in Bruker AVANCE-III 500. I already played
>> with the lock parameters, mainly, those relate to the LOCK LOOP (gain, time
>> and filter), but without any success.
>>
>> I am kindly asking your advice to solve this apparently field drifting
>> problem. What might be the best lock parameters?. This problem happens only
>> on diluted D2O sample solutions, that require a long time acquisition.
>>
>> Regards.
>> Atilano Gutiérrez Carrillo
>> NMR Lab.
>> UAM. Iztapalapa
>> Phone (525) 55- 5804-6541
>>
>>
>>
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>>
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>>
>
Received on Sat Jun 13 2015 - 09:56:02 MST