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This article in SSSAJ

  1. Vol. 67 No. 3, p. 740-746
     
    Received: Mar 29, 2002
    Published: May, 2003


    * Corresponding author(s): weilin.huang@drexel.edu
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doi:10.2136/sssaj2003.7400

Chemical and Molecular Heterogeneity of Humic Acids Repetitively Extracted from a Peat

  1. Li Liab,
  2. Weilin Huang *b,
  3. Ping'an Penga,
  4. Guoying Shenga and
  5. Jiamo Fua
  1. a State Key Lab. of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
    b Dep. of Civil, Architectural, and Environmental Engineering, Drexel Univ., Philadelphia, PA 19104

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.

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Copyright © 2003. Soil Science SocietyPublished in Soil Sci. Soc. Am. J.67:740–746.