In the determination of traces of dissolved vanadium in complex matrices such as seawater, separation and enrichment from the matrix is of special importance. A wide variety of methods has been proposed for preconcentration, depending to the nature of samples and the methods to be used for measurement. Among these methods separation techniques based on sorption on to chelating resins seem convenient, rapid, and capable of achieving a high concentration factor. The methods proposed in this paper are based on the transformation of all dissolved vanadium species in seawater into organic complexes by use of synthetic complexing agents such as dithizone, luminol, or 8-hydroxyquinoline; the resulting vanadium-organic complexes were sorbed on to a C(18) column at a flow rate of 5 mL min(-1). The vanadium sorbed on the C(18) columns was then stripped by use of nitric acid (2 mol L(-1)) and analysed by inductively coupled plasma-atomic emission spectroscopy, ICP-AES. This method was optimised and use of other chelating resins, such as chelamine, chelex-100, and immobilised 8-hydroxyquinoline and was compared by passing seawater samples directly over the resins. The experimental conditions (pH, acid used for elution, and contact time between the liquid sample and the resin) were optimised. The results were compared for all the resins used and were indicative of excellent and coherent reproducibility.

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Total dissolved trace and major metals and their partitioning in porewater sediment have been investigated at two sites in the Seine River estuary (France). For this purpose, solid phase extraction (SPE) has been employed using specific chelating resins for the separation and preconcentration of organic and inorganic forms of studied metals under controlled (N2) inert atmosphere. In fact, the study is focused on the development of a method for sample collection and handling under inert atmosphere in order to avoid some potential artefacts of the extracted porewater, to preserve the samples from possible chemical oxidation changes and to determine metals partitioning between organic and inorganic forms. For this point, a separation and preconcentration method using two columns in series (chelamine and C18 columns) was used. The trace and major metals fixed on the two resins for all determinations were stripped by nitric acid (2 M) and analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Zeeman Graphite Furnace Atomic Absorption Spectroscopy (ZGF-AAS). The relationship between the distribution of metals and physico-chemical parameters such as pH and Eh (redox potential) as a function of depth was discussed. Some tendency in the distributions and seasonal variability of these traces and major metals are improved. The concentrations for all studied metals decreased as a function of depth where iron and manganese were found at mg L(-1) levels and other metals were found at [micro sign]g L(-1) levels, as well as there were significant fractions of all metals (except of manganese) which were complexed by organic matter. The comparison of data for the major elements (Fe and Mn), obtained by direct determination (without preconcentration) and preconcentration, show a very good recovery.

The distribution, mobility, bioavailability, toxicity, bioaccumulation and biodegradability of chemical elements depend not only on their concentrations, but also on their physico-chemical associations with natural systems. [1][2][3][4] Several trace metals occur in natural water distributed between different oxidation states. At equilibrium, the species present are controlled not only by the pH, but also by the redox potential of the system that describes the progress of electron-transfer reactions. 5 The dissolved forms of trace elements are mainly present as free hydrated ions, ion pairs (where the coordinated water is retained), and inorganic and organic complexes with a covalent bound. For example, dissolved trace metals can also form complexes with a wide range of organic and inorganic compounds, depending on the pH, oxidation state, and relative abundance of the complexing agents. The main inorganic compounds are chloride, carbonate, sulfate, hydroxyl, and fluoride; the complexes formed between them and trace metals are almost always very labile. Organic ligands include both biochemical species of low molecular weight (<10 3 ), such as siderophores, carboxylic acids, aminoacids, sugars, small hydroxyacids, 6 etc., and heterogeneous compounds of unknown structure 7-9 with a wide range of relative molecular masses (10 3 -10 7 ). At any rate, there is great certitude that stronger ligands, which are able to complex metal ions, but are not yet completely identified, are present in seawater, most often at very low concentrations. These various forms of organic matters in aquatic systems come largely from living organisms, mainly as polypeptides and polysaccharides in algae exudates, 10 and from pollution sources. Estimating the ligand organic concentration in natural water has until now been a difficult problem. Generally, though the water of open-ocean contains only small amounts of organic matter.The maximum concentration of total organic carbon observed in surface waters is less than 200 µmol/L. 11 Especially prominent among organic matter compounds in aqueous systems are humic substances. These compounds, which result from living matter decay, are a mixture of organic polymers containing charged hydrophobic and hydrophilic groups that possess polyelectrolyte and multifunctional proprieties. In solution, these compounds can occur either in free form, often negatively charged, or bound to others, such as glycine, aspartic acid and alanine. The principle functional groups in humic matter are -COOH, -NH2, -OH and -SH, [12][13][14] It is well-documented that organic compounds form strong complexes with most metals in aquatic systems, and that seawater is a complex medium which contains a large variety of organic and inorganic ligands, including colloidal matter. We suggest that most trace metals are complexed in seawater and that some inorganic metals complexes are either labile or not stable. In contrast, metal-organic complexes are often stable and need various and specific treatments to be dissociated. In t...

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