i had a similar problem before. the user wanted his 1h spectrum in
protonated THF (d4 is too expensive). without tinking too much, i ran
diffusion experiment with ~50% sine gradient. as i recall, it worked fine.
true, you loose some peak because of gradient, but you also gain some as
rg is set higher.
abil
On Tue, 11 May 2004, Robert Harker wrote:
> Guillermo;
>
> The best solution would be to know exactly the source of the noise and
> eliminate it. Do they show up in other samples?
>
> Anyway, have you tried adjusting Receiver Gain manually to a lower level
> than optimum, maybe 1/4 to 1/8 of clipping and then increasing the
> experiment time accordingly to get the S/N desired for peaks of
> interest? Because of non-linearity of most amps and other
> eccentricities it might work better.
>
> Another solution would be still another post-processing solution using a
> mathematical subtraction instead. Regular peaks should not be too tough
> to simulate mathematically if they were close to ideal but you said they
> were ugly. If the are close to perfect little peaks exactly spaced, it
> will work using a fourier series to the nth place. Keep increasing n to
> see what it does.
>
> Something I have not yet seen or read about in any production NMR lab is
> complex electronic (or analog) filtering which is available in other
> research settings (Physics, Astronomy). Pricey! Transients would need
> to be run through extra-fast computerized processors (or custom analog
> circuits) removing previously ID'd signatures before they are added to
> the FID's. One day;)
>
> ///--)\\\
> R. Harker
> UF, NMR Labs, Gainesville Fl 32611-7200
> rharker_at_chem.ufl.edu
> 352-392-4650
>
>
> -----Original Message-----
> From: Zhou, Zhe (ZZ) [mailto:ZZhou_at_dow.com]
> Sent: Monday, May 10, 2004 9:16 AM
> To: 'Guillermo Moyna'; ammrl_at_chemnmr.colorado.edu
> Subject: RE: Eliminating spikes caused by VERY strong signals...
>
>
> Try to use sw less than 25,000Hz and use DQD.
> Adjust RG manually, may be it should be around 1K, do not use RGA.
>
> Good luck.
>
> ZZ
>
> ________________________________
> Zhe Zhou, Ph.D.
> Research Specialist (NMR)
> Molecular Structure Group
> Analytical Sciences, Dow Chemical Company
> 2301 N. Brazosport Blvd., B-1219
> Freeport, TX 77541
> Tel: 979-238-1387
> Fax: 979-238-0752
> Email: zzhou_at_dow.com
>
>
>
> -----Original Message-----
> From: Guillermo Moyna [mailto:g.moyna_at_usip.edu]
> Sent: Friday, May 07, 2004 8:18 AM
> To: ammrl_at_chemnmr.colorado.edu
> Subject: Eliminating spikes caused by VERY strong signals...
>
>
> Hey gang,
>
> I am wondering if someone has encountered this problem before and got a
> solution for it. We are taking 13C spectra of carbohydrates disolved in
> non-deuterated solvents. The solvent peaks are not in the range of the
> sugar peaks, but since the ratio of sugar peaks vs. solvent peaks is
> 1:100, the artifacts (spikes) originating from the solvent peaks start
> showing at regular intervals in the sugar region after extended
> accumulation. They are small enough not to be a major problem, and we
> can identify them because they are always there no matter which sugar
> you are analyzing, but they don't look all that pretty.
>
> Is there any post-processing trick to remove these things? The data is
> being collected on a Bruker AVANCE 400, but due to the chemical shift
> range of the solvent we cannot use DQD. My solution so far is to record
> a spectrum of the neat solvent with the same number of scans and
> substract this from the spectra of the sugars. This works, but I'd like
> to avoid doing it if there's an alternative solution.
>
> TIA,
>
> Guillermo
>
> +==================-------------- --- -- - - - -
> Guillermo Moyna, PhD
> Assistant Professor of Chemistry
> Department of Chemistry & Biochemistry
> University of the Sciences in Philadelphia
> 600 South 43rd Street
> Philadelphia, PA 19104-4495
>
> "The only existing things are atoms and empty space.
> All else is mere opinion" - Democritus, 370 B.C.
>
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> Fax: (215) 596-8543
> e-mail: g.moyna_at_usip.edu
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> http://www.usip.edu/chemistry/faculty/moyna.asp
> - - - - -- --- -----------=================+
>
Received on Wed May 12 2004 - 14:44:09 MST