Catherine Elleouet

Determination of trace amounts of chromium(VI) in water by electrochemical methods

Abstract A sensitive procedure for the determination of chromium(VI) is described. A chelate of chromium with an organic ligand is adsorbed on a hanging mercury drop electrode and the reduction current of the accumulated chelate is measured by differential-pulse voltammetry. The effects of various parameters (pH, ligand concentration, potential and collection time) on the response are discussed. Possible interferences by trace metals and organic matter are considered.

A silver-based metal–organic framework material as a ‘reservoir’ of bactericidal metal ions

The silver-based MOF material Ag3(3-phosphonobenzoate) was evaluated as a bactericidal material. A sustainable release of Ag+, which was quantified by cathodic stripping voltammetry, was responsible for bactericidal activity against the 6 bacterial strains tested.

New FeI–FeI Complex Featuring a Rotated Conformation Related to the [2 Fe]H Subsite of [Fe–Fe] Hydrogenase

Rotated geometry: The first example of a dinuclear iron(I)-iron(I) complex featuring a fully rotated geometry related to the active site of [Fe-Fe] hydrogenase is reported.

Square-Wave Voltammetry of Molybdenum-Fulvic Acid Complex

The reduction process of molybdenum in the presence of fulvic acids was investigated by square-wave voltammetry (SWV). The influence of the parameters (frequency, amplitude) of the SW on the reduction signal is analyzed according to the theoretical model. The molybdenum-fulvic acid complex is reduced reversibly with adsorption of the reactant.

Determination of inorganic and organic selenium species in natural waters by cathodic stripping voltammetry

The determination of the total concentration of a trace element gives only few informations about its toxicity and its bioavailability which depend mainly on the different chemical forms under which it is present. The studies of the chemical speciation is thus particularly important. We propose, in this paper, a selenium speciation model for the studies of natural waters based on Se(IV) voltammetric determination. The separation of the organic and inorganic forms was realized by a rapid ion exchange method and total selenium was determined after a u.v. irradiation.

Coadsorption at the air/water interface likely explains some pollutants transfer to the atmosphere: benzene and lead case

This study attempts to evidence a physical interfacial mechanism for the passing of some non-volatile harmful molecules from water, where they are dissolved, to the atmosphere. The idea developed here is that an organic substance, at its solubility limit, forms a surface layer whose properties induce the coadsorption of another dissolved substance; both are then able to pass to the atmosphere by a bubbling mechanism. Experiments were made with benzene close of its solubility limit in an aqueous solution of lead nitrate, which is non-volatile and normally does not adsorb at water surface. Coadsorption really occurred. The impact of such a mechanism on the environment is discussed.

Speciation Analysis of Selenium in Seawater by Cathodic Stripping Voltammetry

A procedure for the determination of selenium species in seawater is proposed. The speciation scheme is based on different sample treatments followed by the quantification of Se(IV) by differential pulse cathodic stripping voltammetry. To remove the organic matter present in seawater which interferes in the electrochemical step a XAD-2 resin is used. So the selenite concentration can be directly determined. After passage through an IRA 400, selenide is collected in the percolated solution. Following conversion into the tetravalent state, selenium is determined. UV photolysis at basic pH is used to convert all the selenium species to Se(IV) which is the electroactive species. The procedure is applied to seawater samples.

Transfer of highly hydrophilic ions from water to nitrobenzene, studied by three-phase and thin-film modified electrodes.

The study by voltammetry of hydrophilic ion transfers across the interface between an aqueous solution and an immiscible organic solvent is limited by the presence of supporting electrolytes in both phases. Such a study is impossible for ions having a higher affinity for water than ions of the electrolytes. Indirectly, methods based on modified solid electrodes can be used; these are obtained by the deposition of an organic phase containing a molecule having redox properties, the modified electrode being in contact with an aqueous solution of the appropriate electrolyte. The three-phase electrode is very convenient for that purpose. However, this experimental tool also has its own limitation, due mainly to the redox species produced in the organic phase. The oxidized, or reduced, form of the redox molecule must have a very low affinity for water, as otherwise its transfer masks that of the ion under study. Ferrocene is almost useless because of the affinity of the ferrocenium cation for water, decamethylferrocene being a better choice. The present work illustrates how the use of lutetium bisphthalocyanines widely expands the possibilities, as these molecular sandwich complexes can be reduced as well as oxidized, the products of the reactions having a very low affinity for water. This made the determination of the Gibbs energy possible for the transfers of highly hydrophilic ions from water to nitrobenzene: Cl(-) (40 kJ mol(-1)), F(-) (57 kJ mol(-1)), H2PO4(-) (64 kJ mol(-1)). Nothing being really known about the transfer of F(-) or H2PO4(-) from water to organic solvents, these are the first values ever published. H(+), OH(-), and HSO4(-) have also been studied, showing that these species, which have a poor affinity for nitrobenzene, are prone to association reactions with the reduced or oxidized forms of the lutetium bisphthalocyanine.

Electrochemical determination of low levels of residual chlorine dioxide in tap water

The reaction between 1,2-dihydroxyanthraquinone-3-sulphonic acid and chlorine dioxide, in phosphate buffer medium, was studied spectrophotometrically and electrochemically. An electroanalytical method is proposed for the determination of traces of ClO2 with a detection limit of 2 μg l−1. The stoichiometry of the reaction, the effects of various operational parameters and the influence of foreign ions are reported.

Influence of the Dithiolate Bridge on the Oxidative Processes of Diiron Models Related to the Active Site of [FeFe] Hydrogenases

Electrochemical studies of [Fe2 (CO)4 (κ2 -dmpe)(μ-dithiolate)] (dithiolate=adtBn , pdt) and density functional theory (DFT) calculations reveal the striking influence of an amine functionality in the dithiolate bridge on their oxidative properties. [Fe2 (CO)4 (κ2 -dmpe)(μ-adtBn )] (1) undergoes two one-electron oxidation steps, with the first being partially reversible and the second irreversible. When the adtBn bridge is replaced with pdt, a shift of 60 mV towards more positive potentials is observed for the first oxidation whereas 290 mV separate the oxidation potentials of the two cations. Under CO, oxidation of azadithiolate compound 1 occurs according to an ECE process whereas an EC mechanism takes place for the propanedithiolate species 2. The dication species [1-CO]2+ resulting from the two-electron oxidation of 1 has been spectroscopically and structurally characterized. The molecular details underlying the reactivity of oxidized species have been explored by DFT calculations. The differences in the behaviors of 1 and 2 are mainly due to the presence, or not, of favored interactions between the dithiolate bridge and the diiron site depending on the redox states, FeI FeII or FeII FeII , of the complexes.