title: Ultraviolet absorbance titration for determining stability constants of humic substances with Cu(II) and Hg(II).
abstract: We describe an ultraviolet (UV) absorbance titration method that can be used to determine complexing capacities (C(L)) and conditional stability constants (logK) of humic substances (HSs) with metal ions such as Cu(II) and Hg(II). Two fulvic acids (FA) and one humic acid (HA) were used for this study. UV absorbance of HSs gradually increased with the addition of Cu(II) or Hg(II) after blank correction, and these increases followed the theoretical 1:1 (ligand:metal ion) binding model. The results from the absorbance titration calculation for HSs with Cu(II) and Hg(II) compared well with those from fluorescence quenching titration. The titration of the model compound l-tyrosine with Cu(II) proved the validity of this method, and the K and C(L) were within 2.3% and 7.4% of the fluorescence quenching titration. The results suggest that the UV absorbance titration can be used to study the binding capacities of HSs and/or dissolved organic matter (DOM) with trace metals. The advantages and disadvantages of the absorbance titration method were also discussed.
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China.
authors.forename: Y C
authors.initials: YC
authors.lastname: Bai
authors.forename: F C
authors.initials: FC
authors.lastname: Wu
authors.forename: C Q
authors.initials: CQ
authors.lastname: Liu
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.forename: J Y
authors.initials: JY
authors.lastname: Guo
authors.forename: P Q
authors.initials: PQ
authors.lastname: Fu
authors.forename: B S
authors.initials: BS
authors.lastname: Xing
authors.forename: J
authors.initials: J
authors.lastname: Zheng
mesh_terms: D001578:Benzopyrans / Q000032:analysis / Q000528:radiation effects; D003300:Copper / Q000737:chemistry* / Q000528:radiation effects; D005618:Fresh Water / Q000737:chemistry; D006812:Humic Substances / Q000032:analysis* / Q000528:radiation effects; D008628:Mercury / Q000737:chemistry* / Q000528:radiation effects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D017186:Titrimetry / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D014874:Water Pollutants, Chemical; D003300:Copper; D008628:Mercury; C005023:fulvic acid