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Chemical and Molecular Heterogeneity of Humic Acids Repetitively Extracted from a Peat
Author(s) -
Li Li,
Huang Weilin,
Peng Ping'an,
Sheng Guoying,
Fu Jiamo
Publication year - 2003
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2003.7400
Subject(s) - chemistry , size exclusion chromatography , extraction (chemistry) , elemental analysis , peat , carbon 13 nmr , chemical shift , humic acid , carbon fibers , chemical composition , infrared spectroscopy , chemical structure , mass spectrometry , fraction (chemistry) , analytical chemistry (journal) , chromatography , organic chemistry , enzyme , ecology , fertilizer , materials science , composite number , composite material , biology
Eight humic acid (HA) fractions obtained by repetitive base extraction of a peat soil were characterized in terms of chemical compositions, functionalities, and molecular sizes using an elemental analyzer, infrared spectrometry (IR), solid‐state 13 C‐nuclear magnetic resonance spectrometry ( 13 C‐NMR), and high performance size‐exclusion chromatography (HPSEC). Large variations in chemical, functional, and molecular properties were observed among the eight humic fractions. The elemental analysis data showed that, from the first (Fr1) to the eighth fraction (Fr8), the O/C atomic ratio decreased from 0.52 to 0.36 whereas the H/C atomic ratio increased from 1.1 to 1.5. The measured average apparent molecular size (M w ) increases from 7.7 to 22.1 kDa as a function of the extent of extraction. Carbon‐13 NMR and FTIR spectra of the fractions indicated that the contents of oxygen‐containing and aromatic functional groups decreased and the contents of aliphatic groups increased from Fr1 to Fr8. The results suggested that two subunits of HAs might exist: an aliphatic subunit having larger apparent M w and an aromatic subunit having smaller apparent M w We proposed that each of the eight HA fractions is a mixture of these two subunits.