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Complexation of V(IV) and V(V) with succinic and oxalic acids in aqueous acid solution using affinity capillary electrophoresis

Vanadium(V) is a second most abundant trace metal in seawater with characteristic conservative behaviour in open-ocean waters while non-conservative behaviour is reported for coastal waters. There are several possible mechanisms affecting reactivity of V in coastal aquatic systems with the emphasis on deposition of particles, scavenging by terrigenous and/or biogenic material and various adsorption/desorption mechanisms associated with V redox changes [1]. Generally, the distribution of V redox species is controlled by the pH, V concentration, redox potential, ionic strength of the system, chemical composition of natural organic matter and biological activity [2]. Although V(V) is expected to be dominant species in well oxidized marine environments, V(IV) is also previously reported to be present even in surface oxic waters mainly due to its ability to form stable complexes with organic or inorganic ligands in natural waters [1, 3, 4]. The possible formation of such complexes can greatly influence V mobility and toxicity in the aquatic environment [2]. The complexation of V(IV) and V(V) with carboxylic acids (succinic and oxalic acid) in aqueous acid solutions is investigated. Chosen carboxylic acids served as a proxy for Dissolved Organic Matter (DOM) in order to obtain new information on complexation kinetics and equilibrium conditions of V species interaction with more simple organic ligands. The affinity capillary electrophoresis (ACE) has been used to study complexation of V species with succinic and oxalic acids in perchloric acid aqueous medium on fixed conditions of pH (2.0 and 2.5) and ionic strength maintained at 100 mM by NaClO4 additions. In the case of V(IV) complexes with organic ligands, formation of protonated species is suggested. Conversely, in the case of V(V), deprotonated species are suggested. Novel data set on complexation of V with organic ligands is successfully produced.

vanadium ; caroxylic acids ; complex stability

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