Chemical and molecular heterogeneity of humic acids repetitively extracted from a peat

Li Li, Weilin Huang, Ping'an Peng, Guoying Sheng, Jiamo Fu

Research output: Contribution to journalArticlepeer-review

76 Scopus citations

Abstract

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 13C-nuclear magnetic resonance spectrometry (13C-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 (Mw) 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 Mw and an aromatic subunit having smaller apparent Mw. We proposed that each of the eight HA fractions is a mixture of these two subunits.

Original languageEnglish (US)
Pages (from-to)740-746
Number of pages7
JournalSoil Science Society of America Journal
Volume67
Issue number3
DOIs
StatePublished - 2003
Externally publishedYes

ASJC Scopus subject areas

  • Soil Science

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