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Type: Journal article
Title: Impact of remote protonation on 13C CPMAS NMR quantitation of charred and uncharred wood
Author: Smernik, R.
Baldock, J.
Oades, J.
Citation: Solid State Nuclear Magnetic Resonance, 2002; 22(1):71-82
Publisher: Elsevier Science BV
Issue Date: 2002
ISSN: 0926-2040
Statement of
Ronald J. Smernik, Jeffrey A. Baldock and J. Malcolm Oades
Abstract: The impact of inefficient cross polarization (long TCH values), caused by long 13C-1H internuclear distances, on 13C CPMAS NMR spectra of charred and uncharred woods is determined by simultaneously fitting data from complementary variable spin lock and variable contact time experiments. As expected, the impact is minimal for uncharred woods, but is very significant for the charred woods. Quantification of the decrease in CPMAS signal intensity caused by both inefficient cross polarization and rapid T1rhoH relaxation is achieved using an advanced spin counting methodology, for which the term "spin accounting" is proposed. 13C CPMAS NMR observabilities determined using the spin accounting methodology were close to 100% for the uncharred samples, and 69-82% for the charred samples. This represents a large improvement on the 30-40% observabilities determined using other spin counting techniques. Furthermore, it is shown that remote protonation and rapid T1rhoH relaxation are roughly equally responsible for the low signal intensity of standard (I ms contact time) 13C CPMAS spectra of charcoal.
Keywords: Protons; Charcoal; Carbon Isotopes; Magnetic Resonance Spectroscopy; Models, Statistical; Sensitivity and Specificity; Reproducibility of Results; Molecular Structure; Rotation; Wood
Description: Copyright © 2002 Elsevier Science (USA). All rights reserved.
RMID: 0020020492
DOI: 10.1006/snmr.2002.0065
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Appears in Collections:Soil and Land Systems publications

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