Also that kind of ghosts could be related to shims not set correctly (Z3, Z4
and nonspin shims) and quadrature phase detection (QPD). The better way to
detect the first (due to the shims) is with NMR standards for line shape.
The second commonly is observed when you finish an experiment without the
complete phase cycle used for QPD.
For very dilute samples using solvents like acetone, that kind of ghosts are
related to the dymanic range as Woody explained.
Have a nice day,
JOE
On Mar 18, 10:12am, Richard Fronko wrote:
> Subject: Ghosts in the spectrum...
> To all-
>
> We have experienced ghosts or what appears to be artifacts from the
> solvent peak, acetone, in C-13 spectra. These appear at irregular intervals
> from the solvent peak, 4550 Hz, 9524 Hz and 14164 Hz. These are clearly
> ghosts of the main CD3 multiplet at 20 ppm, given the coupling pattern. They
> are negatively phased relative to the main solvent peaks, and
> unfortunately, interfer with the sample peaks.
>
> Does anybody have an idea where these peaks might come from and what we
> can do about it?
>
> *************((((-))))*************
> Richard Fronko
> DCC Manager
> Microcide Pharmaceuticals, Inc.
> 650-428-3516 voice
> 650-526-3034 fax
> *************((((+))))*************
>
>-- End of excerpt from Richard Fronko
>Peaks as you describe can come from non linear responses in the NMR
>instruments detection componets. Things you can try to see if they improve
the situation:
>1. Run at a lower rf gain setting.
>2. Make full use of the digitizer.
>3. Use double precision acquistion.
>4. Use floating point FT.
>In addition, since these things arise from signals mixing (sum and
>difference) at the non linear response site, if the CDCl3 peak is placed at
>the center of the window then the mixing will probably leave the rest of the
>spectrum clear.
>woody@acornnmr.com
-- ____________________________________________________________JOSE R. MARTINEZ ORTIZ Tel. (787)764-0000 x4819 UNIVERSITY OF PUERTO RICO joenmr@uprnmr1.chem.uprr.pr DEPT. OF CHEMISTRY joenmr@worldnet.att.net PO Box 21352 UPR Station http://home.att.net/~joenmr/ San Juan PR 00931-1352 http://uprnmr1.chem.uprr.pr