title: Effects of calcium on the chromophores of dissolved organic matter and their interactions with copper.
abstract: The binding of Ca(2+) and Cu(2+) by dissolved organic matter (DOM) exemplified by Suwannee River Humic Acid (SRHA) was examined in this study. Metal-DOM interactions were quantified using linear and log-transformed DOM absorbance spectra acquired at varying pHs and total Ca(2+) and Cu(2+) concentrations. The binding of Cu(2+) by DOM was examined in the presence of three different Ca(2+) concentrations. Interactions of Ca(2+) with DOM chromophores were accompanied by the emergence of features in the differential spectra that were dissimilar from those characteristic for the binding of Cu(2+). The amount of Ca(2+) and Cu(2+) bound by DOM was ascertained using changes of the slopes of log-transformed absorbance spectra in the range of wavelength 350-400 nm (denoted as S350-400) and comparing the data with model predictions. The observed effects indicated the occurrence of the replacement of a characteristic number of protons by the bound Ca(2+) and Cu(2+) ions.
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195-2700, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Environmental Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China. Electronic address: yanmq@pku.edu.cn.
authors.forename: Mingquan
authors.initials: M
authors.lastname: Yan
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195-2700, United States.
authors.forename: Gregory
authors.initials: G
authors.lastname: Korshin
mesh_terms: D002118:Calcium / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D008956:Models, Chemical; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D006812:Humic Substances; D014874:Water Pollutants, Chemical; D003300:Copper; D002118:Calcium
keywords: Calcium; Competition; Complexation; Copper; Differential absorbance; Dissolved organic matter; NICA-Donnan model