Comparison of solid-state 13C NMR spectra of soil organic matter from an experimental burning site acquired at two field strengths
Ronald J. Smernik A C , Eileen Eckmeier B and Michael W. I. Schmidt BA Soil and Land Systems, School of Earth and Environmental Sciences, The University of Adelaide, Waite Campus, Urrbrae, SA 5064, Australia.
B Department of Geography, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
C Corresponding author. Email: ronald.smernik@adelaide.edu.au
Australian Journal of Soil Research 46(2) 122-127 https://doi.org/10.1071/SR07128
Submitted: 31 August 2007 Accepted: 21 January 2008 Published: 18 March 2008
Abstract
Solid-state 13C cross polarisation (CP) nuclear magnetic resonance spectra were acquired for 15 soil organic matter samples on 2 different spectrometers (200 MHz and 400 MHz). Distributions of broad functional group classes—carboxyl, aryl, O-alkyl, and alkyl—were determined by integration across broad chemical shift regions. The distributions derived from the 2 spectrometers were closely correlated (r2 = 0.77–0.93). Only slight biases were identified; carboxyl C contents were on average 8% lower and alkyl C contents 5% higher for spectra acquired on the 400 MHz spectrometer. These results indicate that valid 13C CP spectra can be acquired at field strengths up to 400 MHz, and that spectra acquired at different field strengths can be directly comparable.
Additional keywords: soil organic matter, cross polarization, solid-state 13C NMR.
Acknowledgments
We thank the experimental burning team members and supporting staff, notably Otto Ehrmann, Reiner Lubberich, and Renate Gerlach for making this research possible. Our sincere thanks go to Jan O. Skjemstad for hosting Eileen Eckmeier in his laboratory and for his assistance.
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