Ionization- and Reduction-Difference Spectra of Humic and Fulvic Acids

Abstract

The ionization difference (δE ₁) and reduction difference (δE _r) spectra of humic acids (HAs) and fulvic acids (FAs) were determined. In the present study, δE ₁, and δE _r spectra refer to the difference spectra between the pH 13 and pH 6 solutions and between the pH 10 and NaBH₄-treated pH 10 solutions, respectively. The δE ₁, spectra of 9 out of 17 samples showed absorption bands due to the 4·9-dihydroxyperylene-3·10-quinone moiety. Based on the δE ₁ spectra, the samples were divided into 4 groups. This grouping was approximately the same as that based on the δE _r spectra. The contribution of the δE ₁ and δE _r spectra to the ordinary absorption spectra was discussed.