Abstract

MOSQUERA, Carmen S; BRAVO, Isabel  and  HANSEN, Eddy W. STRUCTURAL BEHAVIOUR OF HUMIC ACIDS FROM CAUCA DEPARTAMENT ANDISOL SOILCOMPORTAMENTO ESTRUTURAL DOS ÁCIDOS FÚMICOS OBTIDOS DE UM SOLO ANDISOL DO DEPARTAMENTO DO CAUCA. Rev.Colomb.Quim. [online]. 2007, vol.36, n.1, pp.31-41. ISSN 0120-2804.

Humic substances are a heterogeneous mixture of chemical compounds, where each fraction (humic acids, fulvic acids and humin) is constituted by different size molecules. Their structure depends on soil type and environmental conditions. In this study different spectroscopic techniques such as: ultraviolet-visible (ratio E4/E6), infrared Fourier transform (IFT) and solid - state ¹³C nuclear magnetic resonance (NMR) have been used to identify the humic acids (HA) chemical structure, as well as the structural changes taking place in acetic anhydride and absolute ethanol. HA was extracted from organic matter of an Andisol soil in Cauca Department , Colombia , using three basic solutions: Na 2 B 4 O 7 .10H 2 O (0,05M), Na 2 P 2 O 7 .10H 2 O (0,05M) and NaOH (0,1M). Humic acids were purified by acid treatment, HCl - HF 1%, high speed centrifugation and dialysis. The ratio E4/E6 revealed changes on humic acids condensation degree in different chemical environment. These changes were documented by the appearance of new bands and also as changes in relative signal intensity distribution of existing bands in the infrared spectra. Differences in relative intensity distribution of the solid state ¹³C MAS NMR resonance bands were noticed. The present work reveals chemical and structural changes of HA obtained from an agricultural soil, and this study is concordant respect to other studies made in this field.

Keywords : Humic acids; nuclear magnetic resonance; ratio E4/E6; organic matter; organic humified matter; ultraviolet - visible spectroscopic.

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