title: Ultrafiltration and determination of Zn- and Cu-humic substances complexes stability constants.
abstract: This study exhibits that size fractionation of humic substances (HS) and their metal complexes by ultrafiltration is an efficient procedure for simultaneous determination of stability constants. Using sequential-stage ultrafiltration and a radiotracer technique the HS-Cu and HS-Zn complexes studied can gently be size-fractionated and their free metal fractions simply be discriminated. The conditional stability constants Ki obtained for size fractions of these HS metal complexes exhibit a clear molecular size dependence. Accordingly, the highest Ki values (6.6 for Zn and 6.4 for Cu) are found in the HS fractions of >105 kDa. Moreover, the overall stability constants K found for Cu (log K=5.5) and Zn complexes (log K=4.5) of the aquatic HS complexes studied are quite comparable to those reported in the literature.
authors.affiliation: Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin Str. 19, 117975 Moscow, Russia.
authors.forename: T I
authors.initials: TI
authors.lastname: Nifant'eva
authors.forename: P
authors.initials: P
authors.lastname: Burba
authors.forename: O
authors.initials: O
authors.lastname: Fedorova
authors.forename: V M
authors.initials: VM
authors.lastname: Shkinev
authors.forename: B Y
authors.initials: BY
authors.lastname: Spivakov