Thanks to all who have answered to my following request.
Dear all,
We are working with 13C CPMAS NMR of mixtures of crystalline organic
materials.
For quantitative purposes, to get a better determination of the ratio of two
different materials, I would be interested in improving the resolution of
the spectra in a certain region or to get sharper peaks less overlapping or
to shift them to get a better separation....
As we have already tried all the basic and classical tricks we know, my
question is probably stupid but I leave it opened : are there any
possibilities to do that without changing the equipment (i.e. special
sequences, special recording; special processing, solid state shift reagents
(?) etc... etc...).
Any idea ?
Thanks for your help
Francois
=========================================
Dr Francois Croizet
Analytical Chemistry for Development - RX 1114
N.V. Organon - Molenstraat 110
PO Box 20 - 5340 BH Oss - The Netherlands
Tel. +31 (0) 412 66 1130 - Fax. +31 (0) 412 66 3513
E-mail: francois.croizet_at_organon.com
=========================================
=========================================================
>From Johannes Leisen [johannes.leisen_at_tfe.gatech.edu]
=========================================================
Francois,
You should keep in mind, that the 13C chemical shift in solids does also
depend on the conformation of molecules. Hence, especially
noncrystalline solids tend to have very broad lines in CP-MAS and using
higher magnetic fields will not increase the resolution. Crystalline
components will give
relatively narrow lines, but any conformational disorder in the crystals
will broaden the line.
You could try several spectral editing techniques to distinguish between
components. But then it will be very difficult to come up with any
quantification. You might have success with solid state 2D
NMR-techniques like 1H-13C HETCOR, but those are no real routine
experiments.
Regards,
Hanno Leisen
********************************************************
Dr. Johannes Leisen
Research Scientist II
Georgia Institute of Technology
School of Textile & Fiber Engineering
Atlanta/GA 30332-0295
phone: (404) 894-9241; FAX (404) 894-9766
e-mail: johannes.leisen_at_tfe.gatech.edu
=========================================================
>From Prof. Guillermo Mendoza-Díaz [mendozag_at_quijote.ugto.mx]
=========================================================
Dear Francois:
I know it is possible to improve the linewith using a sequence with
phase-modulated decoupling. I know this sequence is made in VARIAN software
and it is call xpolwfg1
I must say that until now I had no need to use it so I do not know how
much is the improvement achieved. Hope this info could help you.
Guillermo Mendoza-Díaz
Universidad de Guanajuato
Facultad de Química
=========================================================
>From Gregory R. Quinting [gregq_at_iei.net]
=========================================================
Francois:
Have you tried recrystallizing the compounds, then grinding the crystals
very fine? The objective being to have 100% crystallinity (nothing
amorphous in other words) and as close as possible to random lattice
orientations. (Those who've thought about the theory more recently than me
might be in a better position to comment and gauge chances of success.) A
luxury would be to spin a single crystal, not knowing if that's possible
with your compounds.
Regards,
Greg
---
Gregory R. Quinting, Ph.D.
Indianapolis, IN USA
=========================================================
>From charlie dickinson [charlie_at_telemann.pse.umass.edu]
=========================================================
We have implemented tppm decoupling and get a bit narrower lines
with less proton decoupling power: I do not have the reference
handy but could look it up if you need it. On our 300 with good
homogeneity we get down to 15-20Hz on crystalline organics spinning
at 5KHz
Received on Tue Jan 29 2002 - 14:07:07 MST