Studying soil organic matter using 13C CP-MAS NMR : The effect of soil chemical pre-treatments on spectra quality and representativity
Articolo
Data di Pubblicazione:
2008
Citazione:
Studying soil organic matter using 13C CP-MAS NMR : The effect of soil chemical pre-treatments on spectra quality and representativity / S. Salati, F. Adani, C. Cosentino, G. Torri. - In: CHEMOSPHERE. - ISSN 0045-6535. - 70:11(2008), pp. 2092-2098. [10.1016/j.chemosphere.2007.08.067]
Abstract:
13C CP-MAS NMR spectroscopy is a technique that has proved to be useful in studying soil organic matter (SOM). Nevertheless, NMR spectra exhibit a weak signal and have very low resolution due to: the low natural abundance of 13C (1.1 % of C) in SOM, the generally low SOM content of soils, and the presence of paramagnetic impurities. This paper studies the effects of soil chemical pre-treatments on 13CP-MAS NMR spectra quality and spectra representativity i.e. soil C mass balance. After chemical pre-treatment to increase total organic carbon (TOC) content and C/Fe ratio, eight soils characterized by different levels of organic carbon content and C/Fe ratios were studied using 13CP-MAS NMR. Moreover, where chemical treatments were not applicable due to high carbon losses, the number of 13CP-MAS NMR scans was increased in order to obtain satisfactory spectra. Results show that chemical pre-treatment of soils with C/Fe > 1 caused high C losses. Bulk soils were therefore studied by increasing the number of 13CP-MAS NMR scans. Acceptable spectra were obtained from 8K scans (1K = 1024 transient). On the other hand, even when a large number of scan (32K) are used, soil with C/Fe < 1 cannot be studied. As these soils are characterized by low C losses after HCl treatments (range of 2.9–25.4%), a pre-treatment of at least 1.39 mol l 1 HCl removes excess Fe and at the same time increases C/Fe ratio resulting in 32K scans providing good spectra.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
13C cross-polarization magic angle spinning NMR spectroscopy ; Chemical treatment ; Organic matter ; Soils
Elenco autori:
S. Salati, F. Adani, C. Cosentino, G. Torri
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