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Characterisation and modelling of marine dissolved organic matter interactions with major and trace cations

Abstract : A two-step protocol (nano-filtration and reverse osmosis) was applied for natural organic matter (NOM) preconcentration of a seawater sample. Complexing affinities of the so concentrated marine dissolved NOM (DNOM) towards major and trace cations were studied by potentiometric and voltammetric titra-tion techniques. The potentiometric titration experiments fitted by models describing and characterising the DNOM–cation interactions, revealed four distinct classes of acidic sites (pKa of 3.6, 4.8, 8.6 and 12). A total acidic sites density of 445 meq/mol C was estimated, with a majority (60%) of carboxylic-like sites. Pseudopolarographic measurements revealed two distinct groups of copper complexes: labile, reducible at about À0.2 V; and inert, directly reducible at about À1.4 V. Simultaneous competition between copper, calcium and proton highlighted the presence of two classes of binding sites (density of 1.72 and 10.25 meq mol À1 C , respectively, corresponding to 3% of total acidic sites). The first class was more specific to copper (log K CuL 9.9, log K CaL 2.5, pKa 8.6), whereas stronger competition between copper and calcium occurred for the second class (log K CuL 6.9, log K CaL 5.5, pKa 8.2). The binding sites characterisation was validated by the very good matching of the non-concentrated seawater sample titration data with the simulated curves obtained using the binding parameters from the concentrated sample. Furthermore, this comparison also validated the applied preconcentration pro-tocol, highlighting its negligible influence on organic matter properties when considering copper complexation.
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Yoann Louis, Cédric Garnier, Véronique Lenoble, Dario Omanovic, Stéphane Mounier, et al.. Characterisation and modelling of marine dissolved organic matter interactions with major and trace cations. Marine Environmental Research, Elsevier science, 2009, 67, pp.100-107. ⟨10.1016/j.marenvres.2008.12.002⟩. ⟨hal-01096834⟩



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