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Spin accounting and RESTORE – two new methods to improve quantitation in solid‐state 13 C NMR analysis of soil organic matter
Author(s) -
Smernik R. J.,
Oades J. M.
Publication year - 2003
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.2003.00497.x
Subject(s) - spectral line , polarization (electrochemistry) , nmr spectra database , chemistry , analytical chemistry (journal) , relaxation (psychology) , nuclear magnetic resonance , physics , chromatography , quantum mechanics , psychology , social psychology
Summary Rapid T 1ρH relaxation and inefficient cross‐polarization have long been known to affect quantitation in solid‐state 13 C cross‐polarization (CP) NMR spectra of soil organic matter. We have developed two new techniques to overcome these problems. The first, spin accounting, enables accurate gauging of how quantitative a spectrum is likely to be. The result is expressed as the percentage of potential NMR signal that can be accounted for ( C obs ). Spin accounting improves on the established spin counting technique by correcting for rapid T 1ρH relaxation and inefficient cross‐polarization. Spin accounting identifies three components: one that is well represented in CP spectra, one that is under‐represented in CP spectra due to rapid T 1ρH relaxation, and one that is under‐represented in CP spectra due to inefficient cross‐polarization. For a range of eight de‐ashed soils, C obs was in the range 83–106%, indicating that virtually all potential signal could be accounted for after correcting for rapid T 1ρH relaxation and inefficient cross‐polarization. The second new technique, RESTORE ( RE storation of S pectra via T CH and T O ne R ho ( T 1ρH ) E diting), generates subspectra for the three components identified in spin accounting. The sum of the three RESTORE subspectra is essentially a corrected CP spectrum. The RESTORE spectra of all eight soils more closely resembled the corresponding, and presumably quantitative, Bloch decay spectra than did the CP spectra. RESTORE identifies the types of structures underestimated by CP, and the cause of their underestimation. Rapid T 1ρH relaxation most affected carbonyl and carbohydrate carbons, whereas inefficient cross‐polarization most affected aromatic carbons.