Speciation analysis of selenium in seawater by cathodic stripping voltammetry

International audienceA 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

Square-wave voltammetry of molybdenum-fulvic acid complex

cited By 34International audienceThe 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 chlorine dioxide, chlorite and chlorate by indigo carmine methods in natural waters: Study of interferences [Determination en milieu naturel du dioxyde de chlore, des ions chlorite et chlorate basee sur l'utilisation du carmin indigo: Etude des interferences]

National audienceOver the last decade, chlorine dioxide has been increasingly used for disinfecting drinking water in many countries. A guarantee for the protection of the consumer is the presence of a sufficient residual concentration of the bactericidal reagent in drinking water. Thus it is important to determine exactly and accurately the levels of chlorine dioxide at the tap. During water treatment and subsequent distribution, chlorine dioxide can undergo a variety of reduction and disproportionation reactions producing primarily chloride but also chlorite and chlorate, which have been shown to cause haemolytic anemia. Reliable analytical methods are needed to identify and determine levels of chlorine dioxide, chlorite and chlorate in drinking water. A procedure based on the use of indigo carmine for the determination of each species in natural waters is suggested in this paper. In phosphate buffer (pH 6.8), two moles of chlorine dioxide oxidize one mole of indigo carmine. The concentration of the bactericidal reagent can be determined by measuring the difference in absorbance of the dye at 610 nm before and after reaction with chlorine dioxide. This method is selective as chlorite and chlorate do not react with indigo carmine in phosphate buffer at pH 6.8. Although the spectrophotometric method can be used successfully used at levels of chlorine dioxide down to 30 μg/l, the determination of lower levels in tap water requires a more sensitive method such as an electrochemical stripping procedure. This analysis is based on the measurement of the decrease in the indigo carmine signal after addition of chlorine dioxide. The detection limit is around 1 μg/l. At pH = 2, one mole of indigo carmine reduces one mole of chlorite. Thus the chlorite concentration can be determined by measuring the indigo carmine absorbance at pH = 2. At pH = 0, indigo carmine reacts with both chlorite and chlorate. A measurement at pH = 0 allows chlorate concentrations to be determined since the decrease in absorbance due to the presence of chlorite can be calculated. The stability of indigo carmine absorbance has been studied. An indigo carmine solution prepared in phosphate buffer is stable over several days if kept in light-proof bottles. It is not surprising that the presence of chlorite and chlorate does not lead to a change in absorbance as they do not react with the dye at pH = 6.8. A slight decrease in absorbance of an indigo carmine solution containing chlorine dioxide is observed after about twenty hours. This means that the chlorine dioxide concentration has to be determined in the first hours, which follow the addition of the dye to the sample in order to avoid errors. Interferences can arise from other residual oxidants, which may also be used in water treatment, or from substances present in the sample, which may react with indigo carmine, chlorite and chlorate. Accordingly, we have considered the influence of humic substances, ozone and hypochlorite. The absorbance of indigo carmine at pH = 2 and at pH = 0 does not change in presence of natural organic matter (1 mg/l). Chlorite and chlorate react with humic substances but the kinetics are much slower than those of the reactions with indigo carmine. Errors arising from humic substances in chlorite and chlorate measurements are thus very weak. Ozone may interfere in analyses as it reacts with indigo carmine. However its existence in the distribution network is unlikely as it also reacts with chlorine dioxide, which is in excess, and chlorite to give chlorate. Hypochlorite causes errors in chlorine dioxide, chlorite and chlorate determinations as a result of a reaction with indigo carmine. In the case of chlorine dioxide determinations, errors can be eliminated by adding ammonia to the sample before indigo carmine. Once the validity of the procedures had been proven in synthetic media, the methods were applied to a natural water, that of the water distribution network of the city of Brest, France. The results have been compared with those of other analytical techniques.A procedure based on the use of indigo carmine for the determination of each species in natural waters is presented. The method is selective as chlorite and chlorate do not react with indigo carmine in phosphate buffer at pH 6.8. Results obtained with this procedure are compared with those of other analytical techniques

Determination of the trace of aluminium (III) in natural fresh water by cathodic redissolution following the adsorption of an aluminium-lumogallion complex [Determination de traces d'aluminium (III) dans les eaux douces naturelles par redissolution cathodique apres adsorption d'un complexe aluminium-lumogallion]

National audienceThis paper describes an electrochemical procedure for the determination of aluminium traces in which pre-concentration is achieved by the adsorption of an aluminium-lumogallion complex onto a hanging mercury drop electrode. The effects of various operational parameters (pH, ligand concentration, potential and accumulation time) on the reduction current of the adsorbed chelate are discussed. Possible interferences by trace metals and organic matter are investigated. A linear current concentration relationship was observed up to 1.5 10-7 mol.L-1. The detection limit is 1.5 10-9 mol.L-1

Determination of the trace of aluminium (III) in natural fresh water by cathodic redissolution following the adsorption of an aluminium-lumogallion complex [Determination de traces d'aluminium (III) dans les eaux douces naturelles par redissolution cathodique apres adsorption d'un complexe aluminium-lumogallion]

National audienceThis paper describes an electrochemical procedure for the determination of aluminium traces in which pre-concentration is achieved by the adsorption of an aluminium-lumogallion complex onto a hanging mercury drop electrode. The effects of various operational parameters (pH, ligand concentration, potential and accumulation time) on the reduction current of the adsorbed chelate are discussed. Possible interferences by trace metals and organic matter are investigated. A linear current concentration relationship was observed up to 1.5 10-7 mol.L-1. The detection limit is 1.5 10-9 mol.L-1

[FeFe]-Hydrogenases Models

International audienceAdvances in Bioorganometallic Chemistry examines the synthesis, structure and reactivity of bioorganometallics, their pharmaceutical applications, hydrogenase, vitamin B12-like systems, and metalloproteins. It is written by the top researchers in the field and compiled by editors Toshikazu Hirao and Toshiyuki Moriuchi. Developments in this new field of bioorganometallic chemistry, a hybrid between biology and organometallic chemistry, happen very quickly and this comprehensive reference offers the latest research and findings in the field. The book features a discussion of the synthesis, structure, and reactivity of bioorganometallics, and an examination of hydrogenase-like systems, which were designed to demonstrate catalytic activities and functional properties. Advances in Bioorganometallic Chemistry also includes a discussion of bioorganometallics as they relate to medicinal chemistry, specifically applications of metalloproteins, metalloenzymes, and applications in bioimaging. The book concludes with coverage of vitamin B12-like systems, including the latest developments in derivatives designed to perform bio-inspired catalytic reactions.Table of Contents1. Synthesis, structure and reactivity2. Hydrogenase3. Medicinal Chemistry and Metallodrugs4. Metalloproteins and metalloenzymes5. Vitamin B1

Determination of chlorine dioxide, chlorite and chlorate by indigo carmine methods in natural waters: Study of interferences [Determination en milieu naturel du dioxyde de chlore, des ions chlorite et chlorate basee sur l'utilisation du carmin indigo: Etude des interferences]

National audienceOver the last decade, chlorine dioxide has been increasingly used for disinfecting drinking water in many countries. A guarantee for the protection of the consumer is the presence of a sufficient residual concentration of the bactericidal reagent in drinking water. Thus it is important to determine exactly and accurately the levels of chlorine dioxide at the tap. During water treatment and subsequent distribution, chlorine dioxide can undergo a variety of reduction and disproportionation reactions producing primarily chloride but also chlorite and chlorate, which have been shown to cause haemolytic anemia. Reliable analytical methods are needed to identify and determine levels of chlorine dioxide, chlorite and chlorate in drinking water. A procedure based on the use of indigo carmine for the determination of each species in natural waters is suggested in this paper. In phosphate buffer (pH 6.8), two moles of chlorine dioxide oxidize one mole of indigo carmine. The concentration of the bactericidal reagent can be determined by measuring the difference in absorbance of the dye at 610 nm before and after reaction with chlorine dioxide. This method is selective as chlorite and chlorate do not react with indigo carmine in phosphate buffer at pH 6.8. Although the spectrophotometric method can be used successfully used at levels of chlorine dioxide down to 30 μg/l, the determination of lower levels in tap water requires a more sensitive method such as an electrochemical stripping procedure. This analysis is based on the measurement of the decrease in the indigo carmine signal after addition of chlorine dioxide. The detection limit is around 1 μg/l. At pH = 2, one mole of indigo carmine reduces one mole of chlorite. Thus the chlorite concentration can be determined by measuring the indigo carmine absorbance at pH = 2. At pH = 0, indigo carmine reacts with both chlorite and chlorate. A measurement at pH = 0 allows chlorate concentrations to be determined since the decrease in absorbance due to the presence of chlorite can be calculated. The stability of indigo carmine absorbance has been studied. An indigo carmine solution prepared in phosphate buffer is stable over several days if kept in light-proof bottles. It is not surprising that the presence of chlorite and chlorate does not lead to a change in absorbance as they do not react with the dye at pH = 6.8. A slight decrease in absorbance of an indigo carmine solution containing chlorine dioxide is observed after about twenty hours. This means that the chlorine dioxide concentration has to be determined in the first hours, which follow the addition of the dye to the sample in order to avoid errors. Interferences can arise from other residual oxidants, which may also be used in water treatment, or from substances present in the sample, which may react with indigo carmine, chlorite and chlorate. Accordingly, we have considered the influence of humic substances, ozone and hypochlorite. The absorbance of indigo carmine at pH = 2 and at pH = 0 does not change in presence of natural organic matter (1 mg/l). Chlorite and chlorate react with humic substances but the kinetics are much slower than those of the reactions with indigo carmine. Errors arising from humic substances in chlorite and chlorate measurements are thus very weak. Ozone may interfere in analyses as it reacts with indigo carmine. However its existence in the distribution network is unlikely as it also reacts with chlorine dioxide, which is in excess, and chlorite to give chlorate. Hypochlorite causes errors in chlorine dioxide, chlorite and chlorate determinations as a result of a reaction with indigo carmine. In the case of chlorine dioxide determinations, errors can be eliminated by adding ammonia to the sample before indigo carmine. Once the validity of the procedures had been proven in synthetic media, the methods were applied to a natural water, that of the water distribution network of the city of Brest, France. The results have been compared with those of other analytical techniques.A procedure based on the use of indigo carmine for the determination of each species in natural waters is presented. The method is selective as chlorite and chlorate do not react with indigo carmine in phosphate buffer at pH 6.8. Results obtained with this procedure are compared with those of other analytical techniques

Role of a Redox-Active Ligand Close to a Dinuclear Activating Framework

International audienc

Electron transfer between a lutetium bisphthalocyanine and FeIII/II across liquid|liquid interfaces between water and dichlorohexane or nitrobenzene; influence of coupling with ion transfer

International audienceThe electron transfer across the liquid|liquid interface between aqueous solutions (W) of FeIII/II compounds (hexacyanoferrates, chlorides) and a (t-butyl) substituted LuIIIbisphthalocyanine in dichlorohexane (DCH) or nitrobenzene (NB), has been studied by voltammetry at a microinterface and by spectrophotometry. The electron transfer wave has been observed only at the W|DCH. Coupling with an ion transfer facilitates this electron transfer: the LuIIIbisphthalocyanine has been oxidized or reduced across the W|NB interface, depending on the ion establishing the interfacial potential

Studying the thermodynamics and kinetics of ion tranfers across water-2-nitrophenyloctyl ether interface by means of organic solution modified electrodes

International audienceTransfer reactions across water-2-nitrophenyloctyl ether (W|NPOE) interface for a series of monovalent inorganic ions and tetraalkylammonium cations are studied by means of square-wave (SWV) and cyclic voltammetry at thin organic-film-modified (TFE) and three-phase electrodes (TPE). Both electrode configurations are assembled using lutetium bis(tetra-tert-butylphthalocyaninato) as a redox probe, whose redox properties enable assessment of both anion and cation transfer reactions in a single voltammetric experiment. It is demonstrated that TFE can be effectively applied to measure the Gibbs energy of ion transfer reactions when the transferring ion is a common ion for both liquid phases, controlling the Galvani potential difference at the W|NPOE interface. A comparative study of the thermodynamics of ion transfer reactions performed with TFE and TPE reveals that both electrode configurations provide a consistent set of data. Kinetic measurements referring to the transfers of ClO4-, and a series of tetraalkylammonium cations have been conducted by combining TFE and SWV according to the method known as “quasireversible maximum” in thin-film voltammetry (Mirčeski, V. J. Phys. Chem. B 2004, 108, 13719)