Journal Article

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

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

2003

Overview

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 ^sup 13^C-nuclear magnetic resonance spectrometry (^sup 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^sub 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^sub w^, and an aromatic subunit having smaller apparent M^sub w^. We proposed that each of the eight HA fractions is a mixture of these two subunits.

• Publisher: Soil Science Society of America,American Society of Agronomy
• Subject: Biological and medical sciences / Carbon 13 / Fundamental and applied biological sciences. Psychology / Heterogeneity / Humic acids / NMR / Nuclear magnetic resonance / Organic chemistry / Peat / Peat soils / Soils / Spectrometry