FT-IR Spectra of Soil Constituents: Fulvic Acid and Fulvic Acid Complex with Ferric Ions

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Abstract
FT-IR spectra and corresponding second-derivative spectra, as well as pertinent difference spectra, of fulvic acid and of fulvic acid complexed with ferric ions have been obtained. The data reveal that the major functional groups present in the fulvic acid studied are carboxyl groupings and CH2 groupings of hydrocarbon chains. The presence of ferric ions results in increased ionization of the COOH groups to form COO− ions, as well as a change of the characteristic COO− stretching frequencies of the carboxylate ions. The data thus indicate that ferric ions in soils interact with carboxylate ions of fulvic acids. The second-derivative spectra permit the identification of certain alkyl and aromatic hydrocarbon vibrational modes which cannot be observed in the original FT-IR spectra.