Sequential exhaustive extraction of a Mollisol soil, and characterizations of humic components, including humin, by solid and solution state NMR

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doi: 10.1111/j.1365-2389.2007.01006.x
Authors:Song, G.; Novotny, E. H.; Simpson, A. J.; Clapp, C. E.; Hayes, M. H. B.
Author Affiliations:Primary:
Department of Chemical and Environmental Sciences, University of Limerick, LImerick, Ireland
University of Toronto at Scarborough, Canada
University of Minnesota, United States
Volume Title:European Journal of Soil Science
Source:European Journal of Soil Science, 59(3), p.505-516. Publisher: Wiley-Blackwell on behalf of the British Society of Soil Science, and the National Societies of Soil Science in Europe, Oxford, United Kingdom. ISSN: 1351-0754
Publication Date:2008
Note:In English. 66 refs.; illus., incl. 1 table
Summary:A sequential extraction procedure was applied to isolate soil organic components using aqueous solvents at different pH values, base plus urea (base-urea), and dimethylsulfoxide (DMSO) plus conc. H2SO4 (DMSO-acid) for the humin-enriched clay separates. Extracts from base-urea and DMSO-acid would be regarded as 'humin' in classical definitions. The fractions isolated from aqueous base, base-urea and DMSO-acid were characterized by solid and solution state NMR spectroscopy. The base-urea solvent system isolated ∼10% (by mass) additional humic substances. The combined base-urea and DMSO-acid solvents isolated ∼ 93% of total organic carbon from the humin-enriched fine clay fraction (<2 µm). Characterization of the humic fractions by solid-state NMR spectroscopy showed that oxidized char materials were concentrated. in humic acids isolated at pH 7, and in the base-urea extract. Lignin-derived materials were in considerable abundance in the humic acids isolated at pH 12.6. Only very small amounts of char-derived structures were contained in the fulvic acids and fulvic acids-like material isolated from the base-urea solvent. After extraction with base-urea, the 0.5 M NaOH extract from the humin-enriched clay was predominantly composed of aliphatic hydrocarbon groups, with lesser amounts of aromatic carbon (probably including some char material), and carbohydrates and peptides. From the combination of solid and solution-state NMR spectroscopy, it is clear that the major components of humin materials, from the DMSO-acid solvent, after the exhaustive extraction sequence, were composed of microbial and plant derived components, mainly long-chain aliphatic species (including fatty acids/ester, waxes, lipids and cuticular material), carbohydrate, peptides/proteins, lignin derivatives, lipoprotein and peptidoglycan (major structural components in bacteria cell walls). Black carbon or char materials were enriched in humic acids isolated at pH 7 and humic acids-like material isolated in the base-urea medium, indicating that urea can liberate char-derived hydrogen-bonded material or that trapped within the humin matrix. [G.L.B.]
Subsections:Organic geochemistry; Petrology; weathering; soils
Subjects:Aliphatic hydrocarbons; Aromatic hydrocarbons; Carbohydrates; Carbon; Characterization; Clastic sediments; Clay; Fulvic acids; Humic acids; Humic substances; Hydrocarbons; Lignin; Methods; Mollisols; NMR spectra; Organic acids; Organic carbon; Organic compounds; Peptides; PH; Proteins; Sediments; Sequential extraction; Soils; Solvents; Spectra; Soil organic matter
Abstract Numbers:08M/2285
Record ID:2016108131
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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