Spectroscopic and structural characterization of a Laurentian fulvic acid: notes on the origin of the color

The results of a study in which ultrafiltration fractionation in combination with UV_VIS, fluorescence, FT-IR and NMR spectroscopy was used to characterize a stoichiometrically characterized Laurentian fulvic acid are presented. The non-additivity of the spectra supports the hypothesis that the characteristic brown color of fulvic acid results from donor-acceptor interactions which shift to the red and broader constituent chromophoric bands. The study includes evaluation of the binding behavior of the polar herbicide atrazine with different fulvic acid fractions and the interactions among fulvic acid fractions themselves. Binding is mainly by the largest molecular weight fraction and competition occurs between attrazine and lower molecular weight fractions of fulvic acid.