Chemical and spectroscopic characterization of humic acids from a soil toposequence in Venezuela
1998
Rivero, C. | Paolini, J. | Senesi, N. | DiOrazio, V.
An investigation was conducted on physicochemical properties of humic acids (HAs) in Venezuelan soils. The HAs were extracted by the NaOH method from a Banco-Bajio-Estero soil toposequence (local names for soils located at high, intermediate and low topographic levels), in the Venezuelan plains (Mantecal, Apure State). The extracted HAs were analyzed for elemental composition and characterized by fluorescence, Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies. The results showed that free radical concentration of HAs increased from soils at the highest to soils at the lowest topographic position. High carbon (C), nitrogen (N), and carboxyl group contents, E4/E6 ratio, aliphatic character and concentration of free radicals, and low oxygen (O) and phenolic hydroxyl group contents and total acidity were typical of HA from soils at the lower relief position. The FT-IR spectra indicated that the HA from the soil at the lowest topographic position tended to have a slightly higher content of carboxyl groups than the HAs from soils at higher topographic levels. The observed fluorescence was attributed to the presence of condensed aromatic moieties and/or conjugated unsaturated systems of various complexity in the HA macromolecules.
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