title: Acid-base characterization of molecular weight fractionated humic acid.
abstract: Acid-base properties of molecular weight fractionated humic acids (HAs) were investigated by the acid-base potentiometric titration. The acidic group contents (C(A(t))) and the average values of apparent pK (pK(app)) were evaluated by applying a modified Henderson-Hasselbalch equation to the experimental titration curves. The average values of pK(app) of the fractionated and unfractionated HAs were about 4.1-4.4, and the distribution of pK(app) values could be represented by the relationships between alpha and pK(app) plots in the range 2-8. The C(A(t)) values increased with a decrease in molecular size, as did the aromaticity. This suggests that the acidic group contents are related to the aromaticity of the HA.
authors.affiliation: Division of Material Science, Graduate School of Environmental Earth Science, Hokkaido University, 060 Sapporo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Fukushima
authors.forename: S
authors.initials: S
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Nakamura
authors.forename: S
authors.initials: S
authors.lastname: Ito