title: In-Situ Investigation of Interactions between Magnesium Ion and Natural Organic Matter.
abstract: Natural organic matter (NOM) generated in all niches of the environment constitutes a large fraction of the global pool of organic carbon while magnesium is one of the most abundant elements that has multiple roles in both biotic and abiotic processes. Although interactions between Mg(2+) and NOM have been recognized to affect many environmental processes, little is understood about relevant mechanisms and equilibria. This study addressed this deficiency and quantified Mg(2+)-NOM interactions using differential absorbance spectroscopy (DAS) in combination with the NICA-Donnan speciation model. DAS data were obtained for varying total Mg concentrations, pHs from 5.0 to 11.0 and ionic strengths from 0.001 to 0.3 mol L(-1). DAS results demonstrated the existence of strong interactions between magnesium and NOM at all examined conditions and demonstrated that the binding of Mg(2+) by NOM was accompanied by the replacement of protons in the protonation-active phenolic and carboxylic groups. The slope of the log-transformed absorbance spectra of NOM in the range of wavelength 350-400 nm was found to be indicative of the extent of Mg(2+)-NOM binding. The differential and absolute values of the spectral slopes were strongly correlated with the amount of NOM-bound Mg(2+) ions and with the concentrations of NOM-bound protons.
authors.affiliation: †Department of Environmental Engineering, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Peking University, Beijing 100871, China.
authors.forename: Mingquan
authors.initials: M
authors.lastname: Yan
authors.affiliation: ‡College of Chemistry and Chemical Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Lu
authors.affiliation: §Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, Washington 98195-2700, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.affiliation: ∥Institut de Physique du Globe de Paris-Sorbonne Paris Cité-Université Paris-Diderot, UMR CNRS 7154, Paris, France.
authors.forename: Marc F
authors.initials: MF
authors.lastname: Benedetti
authors.affiliation: §Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, Washington 98195-2700, United States.
authors.forename: Gregory V
authors.initials: GV
authors.lastname: Korshin
mesh_terms: D002264:Carboxylic Acids / Q000032:analysis; D006812:Humic Substances / Q000032:analysis; D007477:Ions; D008274:Magnesium / Q000737:chemistry*; D009930:Organic Chemicals / Q000032:analysis*; D009994:Osmolar Concentration; D011522:Protons; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002264:Carboxylic Acids; D006812:Humic Substances; D007477:Ions; D009930:Organic Chemicals; D011522:Protons; D008274:Magnesium