Elementary composition, IR spectra, 13C-NMR spectra and molecular size distribution were determined for fulvic acids (FAs), polyvinylpyrrolidone (PVP)-adsorbed and non-adsorbed fractions of FAs and humic acids (HAs). The analytical data showed that the properties were distinctly different between the PVP-adsorbed and the non-adsorbed fractions. Atomic ratio, IR spectra and 13C-NMR spectra indicated that the PVP-adsorbed fractions contained a larger number of aromatic rings and carboxyl groups including ester than the non-adsorbed fractions. On the other hand, carbohydrates and N-containing compounds such as peptides or amino acids were concentrated in the PVP-non-adsorbed fractions. Weight average molecular weights (Mw ) of the adsorbed fractions were lower and the range of molecular size distribution was narrower than those of the non-adsorbed fractions. Chemical characteristics of HAs varied depending on the types of soils, while the characteristics of the PVP-adsorbed and non-adsorbed fractions of FAs were similar in the various types of soils.
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Watanabe et al. (1992) studied this question.
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