RE: Ghosts in the spectrum...

Woodrow W. Conover (woody@acornnmr.com)
Wed, 18 Mar 1998 12:55:38 -0800

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

> -----Original Message-----
> From: Richard Fronko [mailto:rfronko@microcide.com]
> Sent: Wednesday, March 18, 1998 10:13 AM
> To: AMMRL 1998
> Cc: Julie Lee; Andrew Staley
> 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
> *************((((+))))*************
>
>