Les possibilités et limitations de l'atomisation électrothermique en spectrom/'etrie d'absorption atomique lors de l'analyse directe des metaux lourds dans l'eau de mer

This work shows the analytical possibilities of an electrothermal atomizer for the direct determination of trace metals in sea-water.The high background signals generated by the matrix perturb in particular volatile elements because of the low decomposition temperature allowed. In the case of cadmium, addition of ascorbic acid to the sample permits the modification of the atomization mechanism and the reduction of the optimum temperature. Under these conditions, absorption peak of the cadmium precedes the background absorption and consequently the analysis is no longer limited by the magnitude of the matrix signal: the determination of cadmium concentrations far below the μg^?1 level is easily possible. Although the direct determination of the other elements should be in principle less disturbed by the background, the analytical performance is poorer than for cadmium. Limits of determination of the order from 0.1 to 1 μg^?1 can be reached for chromium, copper and manganese. Lead and nickel appeared to be the most difficult elements; their direct determination is only possible in polluted coastal or estuarine waters.The injection of the sample as an aerosol into hot graphite tube showed to be well adapted to this kind of investigations. The simultaneous visualization of specific and background signals allows interpretations which until now were impossible with commercially available apparatus.     

Different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry: Cadmium determination in whole blood as a case study

In the present work the performance of different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry was investigated, using the determination of Cd in whole blood as an example. Grooved, integrated and fork platforms as well as atomization temperatures between 1200 °C and 2200 °C were investigated in a longitudinally heated graphite atomizer and compared with the performance of a transversely heated furnace. In the longitudinally heated furnace the increase of the atomization temperature in the studied range resulted in an increase of matrix effects for all platform geometries. The integrated platform exhibited slightly lower sensitivity and increased multiplicative interferences in comparison to the other two platform designs. Interference-free Cd determination was possible with all types of platforms and 1200 °C as the atomization temperature as well as with grooved and fork platforms at 1700 °C. On the other hand, lower atomization temperatures resulted in poorer limits of detection, due to the longer integration time needed. No matrix effect was observed at any atomization temperature using the transversely heated atomizer; in addition, limits of detection were better than those observed with the longitudinally heated atomizer. Best values were around 0.02 μg L^− 1 with the latter atomizer compared to values around 0.02 μg L^− 1 with the former one.     

Comparative study of conventional and multivariate methods for aluminum determination in soft drinks by graphite furnace atomic absorption spectrometry

In the present study, conventional and multivariate methods were used to optimize conditions for direct determination of aluminum in soft drinks by electrothermal atomic absorption spectrometry. For the conventional method, the optimized experimental parameters were: pyrolysis and atomization temperatures and chemical modifier. A multivariate study was performed using factorial design and the optimized parameters were the same employed in the univariate method including pyrolysis time. For the conventional method, the optimal conditions obtained were: pyrolysis temperature of 1600 °C, atomization temperature of 2700 °C, and Zr as permanent modifier. For the factorial design in the multivariate optimization, the Pareto´s chart showed that the atomization temperature, the modifier, and the pyrolysis temperature presented a significant effect on the integrated absorbance and the interaction between pyrolysis temperature and pyrolysis time also had a significant effect on the signal. Better results were obtained using Zr as modifier. The surface response indicates that the lowest pyrolysis (1100 °C) and atomization temperatures (2350 °C) provide higher absorbance for aluminum in soft drinks. Characteristic mass of 23.4 and 19.4 pg and LOD of 17.9 and 11.3 μg L^− 1 was obtained to conventional and multivariate methods, respectively. The calibration was accomplished with standard addition in a range of 60–200 μg L^− 1 for conventional method and of 38–200 μg L^− 1for multivariate method with R higher than 0.99 for both conditions. Recoveries in both studies were nearly 100% with adequate precision for GFAAS analysis. For the Al concentrations level found in soft drinks, both experimental conditions are adequate as good results were obtained in recovery studies. The Al concentrations in different soft drinks range from 147.9 to 599.5 μg L⁻¹. Higher concentrations were found in soft drinks sold in Al cans than in PET bottles, indicating that contamination can occur.     

Synthèse et stabilité sous irradiation électronique d'une céramique Ba1,16Al2,32Ti5,68O16 de structure hollandite envisagée pour le confinement de césium radioactif

Synthesis and stability under electron irradiation of a hollandite structure-type Ba_1.16Al_2.32Ti_5.68O₁₆ ceramic envisaged for radioactive cesium immobilization. Hollandite structure-type Ba_xCs_y(M,Ti)₈O₁₆ (x + y < 2, M trivalent cation) ceramics are currently envisaged as a specific waste form for radioactive cesium immobilization. In order to simulate the effect of cesium β decay on this kind of matrix, the structural modifications and the paramagnetic point defects induced by external electron irradiations near room temperature in a simplified Ba_1.16Al_2.32Ti_5.68O₁₆ hollandite composition were studied mainly by EPR and NMR. Modifications of Al³⁺ and Ti⁴⁺ ions' environment were observed and are due to both the formation of oxygen vacancies and to barium ions displacement. Electron (Ti³⁺) and hole (O₂⁻) centres were observed. The stability of these centres was good at room temperature but thermal treatments performed between 50 and 850 °C generated new paramagnetic defects originating from previous defects. These new defects correspond to titanyl-type Ti³⁺ ions located on grain surface and to oxygen aggregates in their bulk.     

Propriétés électriques du trioxyde de tungstène a proximité de sa composition stoechiométrique. Influence des conditions thermodynamiques de préparation et phénomènes de trempe

The experimental study of variations in electrical conductivity of WO_3−x vs oxygen partial pressure and temperature shows evidence of interstitial W⁶_i· as being the major defect. Under certain conditions, point defects can order themselves in extended defects. The behavior of electrical conductivity can be interpreted in terms of thermodynamic equilibrium between point defects and extended defects, the latter leading to structural modifications beyond a certain departure from stoichiometry. Moreover, WO_3−x shows evidence of quenching phenomena allowing it to keep electrical features characteristic of high temperatures down to room temperature. These properties may explain discrepancies between previous data.     

Éléments chimiques à considérer dans l’aval du cycle nucléaire

Chemical elements to be considered in back end of nuclear cycle. Chemistry dealing with nuclear energy needs to know the chemical behaviour of many elements and radioelements (natural and artificial) under ionising radiation. Their isotopic composition depends on events that arise in nuclear reactors, where stable and radioactive nuclei are produced by nuclear processes. Fission of heavy nuclei gives fission products that are stable or radioactive isotopes of medium mass elements and neutrons. In the conditions prevailing in nuclear reactors, neutrons give isotopes of actinides and activation products, isotopes of various elements. Characteristics of their productions are given. About 40 elements are concerned. To cite this article: R. Guillaumont, C. R. Chimie 7 (2004).     

Fe2PO5, un phosphate de fer de valence mixte. Préparation et études structurale, mössbauer et magnétique

Fe₂PO₅ is prepared from diverse components of the Fe---P---O system at 900°C in sealed silica tubes in vacuum. The study of a single crystal shows an orthorhombic cell, space group Pnma, with a = 7.378, B = 6.445, C = 7.471 Å and Z = 4. The structure is determined through direct methods and Fourier syntheses and refined to R = 0.027. The phosphorus fills isolated tetrahedra. The Fe^II and Fe^III ions are ordered in distorted octahedra: the octahedra surrounding Fe^II build strings parallel to the b axis and share edges; the octahedra containing Fe^III are connected on both sides of these strings alternatively with the PO₄ tetrahedra. The two types of octahedra share one face. Such an arrangement strongly recalls two out of the three Al₂SiO₅ polymorphs, namely, the kyanite and sillimanite. The Mössbauer spectroscopy exhibits a magnetic transition at 220 K. Below, the spectrum shows a six-line hyperfine pattern for Fe^III and an eight-lines one for Fe^II with a rather weak hyperfine field; above, there are two well differentiated doublets, confirming the absence of electronic charge transfer at room temperature. The magnetic susceptibility, recorded from 90 to 300 K, is typically that of an antiferromagnetic compound with C_M = 7.12, θ_p = −350 K and T_N 250 K. The magnetic interactions are discussed. The electronic localization is explained through structural and crystal field considerations; the electrostatic potential difference between the Fe^II and Fe^III sites is calculated.     

Ultratrace determination of tin by hydride generation in-atomizer trapping atomic absorption spectrometry

A quartz multiatomizer with its inlet arm modified to serve as a trap (trap-and-atomizer device) was employed to trap tin hydride and subsequently to volatilize collected analyte species with atomic absorption spectrometric detection. Generation, atomization and preconcentration conditions were optimized and analytical figures of merit of both on-line atomization as well as preconcentration modes were quantified. Preconcentration efficiency of 95 ± 5% was found. The detection limits reached were 0.029 and 0.14 ng mL⁻¹ Sn, respectively, for 120 s preconcentration period and on-line atomization mode without any preconcentration. The interference extent of other hydride forming elements (As, Se, Sb and Bi) on tin determination was found negligible in both modes of operation. The applicability of the developed preconcentration method was verified by Sn determination in a certified reference material as well as by analysis of real samples.     

Untersuchungen zur atomspektroskopischen spurenanalyse in AIIIBV-halbleiter-mikroproben—V: Bestimmung von selen- und tellurspuren in anorganischen matrices durch aas mit direkter elektrothermischer verdampfung in einer graphitrohrküvette und durch aas im quarzrohratomisator nach hydriderzeugung—untersuchung der matrixeffekte und methodenvergleich

The determination of traces of Se and Te by AAS with generation of volatile hydrides and atomization in a quartz tube, and by AAS with direct electrothermal atomization in a graphite cuvette, is described. The instrumental parameters and the experimental conditions were optimized. For pure acidic solutions it was found best to determine selenium by the hydride technique and tellurium by direct electrothermal atomization. The influence of A^IIIB^V-matrices, and of other substances which also form volatile hydrides, on the determination of Se and Te was investigated. When the hydride technique was used it was found that the main causes of the depression of the AA signals are the formation of insoluble compounds between the matrix and H₂Se or H₂Te, and the loss of NaBH₄ by reaction with reducible compounds. In the case of the graphite cuvette the formation of stable molecules in the plasma and increased light-scattering are the main causes of interference. The analytical possibilities of the methods are compared and the advantages and disadvantages are described.     

A pyrolysis-GC–MS investigation of poly(vinyl phenyl ketone)

The thermal decomposition process and pyrolysis products of poly(vinyl phenyl ketone) (PVPK) were investigated by thermogravimetric analysis (TGA) and on-line pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS). TGA showed a largest weight loss rate around 380 °C. Py-GC–MS was used for the qualitative analysis of the pyrolysis products at 350, 500, 600, 700 and 850 °C. The major volatile thermal decomposition product was found to be 1-phenyl-2-propenone, which dominated all other volatile species especially under the least severe pyrolysis conditions (<600 °C). At higher temperatures a much wider range of pyrolysis products was obtained. The results have been interpreted assuming that primary random chain scission reactions occur followed by typical unzipping mainly producing monomer units; detachment of the side-group occurs only under more severe pyrolysis conditions. Py-GC–MS showed to be effective in PVPK detection in ink and paint formulations.     

The application of electrodeposition on a tungsten wire to furnace atomic absorption spectrometry

This work utilizes electrolytic separation and preconcentration of analyte metals on a thin tungsten wire electrode prior to their determination by furnace atomic absorption spectrometry (AAS). Only a very basic electrolysis system operating at constant applied voltages is needed. Following the deposition step, the wire electrode is inserted into the central region of a miniature CRA 90 furnace and electodeposited metals atomized. Tungsten wire melts in the furnace environment at approximately 2500°C and this restricts the range of metals which can be determined by this technique. So far, elements characterized by relatively low atomization temperatures, such as Cd, Zn, Ag, Pb and Cu, have been studied. Sensitivity improvements ranging from 1.5 to 15-fold over the conventional furnace AAS have been achieved with deposition times between 30 and 300 s. No appreciable background absorption has resulted during the atomization step following depositions from NaCl solutions, confirming very efficient separation. The technique has been successfully applied to the determinations of Pb in blood digest and in seawater. Apart from the analytical applications, the wire deposition approach to furnace atomization offers some more fundamental advantages over systems operated in the conventional manner. It can be used to study the atomization behaviour of elements in metallic form in relation to the atomization of their different compounds. Moreover, by rapidly introducing the wire into the furnace preheated to a constant temperature, very fast atomization is achieved with corresponding improvements in analytical sensitivities. The rapid wire introduction technique also lends itself to studies of the removal of sample vapour from furnaces.     

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO₃)₂·6H₂O and Si(OC₂H₅)₄ using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N₂ adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co²⁺ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co²⁺ tetrahedral complexes, while at higher cobalt loading Co₃O₄ was present as the only crystalline phase, besides Co²⁺ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co₂SiO₄ was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.     

Novel zinc ion conducting polymer gel electrolytes based on ionic liquids

We report novel zinc ion conducting polymer gel electrolytes (PGEs) based on non-volatile room temperature ionic liquids. The PGEs consist of an ionic liquid, with a zinc salt dissolved in it, blended with a polymer matrix, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The resultant electrolyte membranes are freestanding, translucent, flexible and elastic, with excellent mechanical integrity and strength. They possess exceptional thermal stability, exhibit essentially no weight loss under dynamic vacuum or upon heating to 200 °C, and remain the same gel phase in wide temperature ranges, with ionic conductivities on the order of 10⁻³ S/cm at room temperature, 10⁻⁴ S/cm at −20 °C and 4–5 × 10⁻³ S/cm at 80 °C. Electrochemical tests show that zinc ions are mobile in the membranes and zinc metal is capable of dissolution into and deposition from the membranes. The membranes also exhibit wide electrochemical stability windows. The results of this study demonstrate the promise of developing PGEs based on ionic liquids for potential application in next-generation non-aqueous zinc battery systems.     

Thermodynamique de composes azotes III. Etude Thermochimique de la glycine et de la l-α-alanine

The enthalpies of formation of glycine and L-α-alanine are determined by two complementary techniques: combustion calorimetry and change of state (sublimation) calorimetry.

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The values of the experimental and theoretical energy of conjugation of these two molecules (partially conjugated) and the energetical value of the C---N bond in Laidler's scheme, derived from the experimental enthalpy of atomization, are also given.

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Résumé

Les enthalpies de combustion à létat condensé de la glycine et de la L-α-alanine ont été déterminées à d'un calorìmetre isopéribolique à bombe rotative. Leurs valeurs à l'état standard à 298,15 K sont: δH°_c = −(972,98±0,19) kJ mol⁻¹ pour la glycine et ΔHδ_c = −(1621,45 − 0,48) kJ mol^-1 pour la L-α-alanine. Les enthalpies de sublimation à l'état standard à 298,15 K ont été obtenues par calori-     

Oxidation of propane over substituted Keggin phosphomolybdate salts

Ammonium salts, (NH₄)₆HPMo₁₁MO₄₀ (M = Ni, Co, Fe), have been investigated for the oxidation of propane, with molecular oxygen, at temperature ranging between 380 °C and 420 °Cafter in-situ pre-treatment performed at two heating rate of 5 or 9 °C/min. They were characterized by BET method, XRD, ³¹P NMR, UV-Vis and IR techniques. The catalysts were found active in the propane oxidation and selective to propene or acrolein, in particular for samples pre-treated with the heating rate of 9 °C/min.     

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.     

TGA–FTIR study of a lead zirconate titanate gel made from a triol-based sol–gel system

A Pb(Zr,Ti)O₃ precursor gel made from a sol prepared using 1,1,1,-tris(hydroxymethyl)ethane, lead acetate and zirconium and titanium propoxides, stabilised with acetylacetone, was analysed using TGA–FTIR analysis. Decomposition under nitrogen (N₂) gave rise to evolved gas absorbance peaks at 215 °C, 279 °C, 300 °C and 386 °C, but organic vapours continued to be evolved, along with CO₂ and CO until 950 °C. The final TGA step in N₂ is thought to relate to decomposition of an intermediate carbonate phase and the final elimination of residues of triol or acetylacetonate species which form part of the polymeric gel structure. By contrast, heating in air promoted oxidative pyrolysis of the final organic groups at ≤450 °C. In air, an intermediate carbonate phase was decomposed by heating at 550 °C, allowing Pb(Zr,Ti)O₃ to be produced some 400 °C below the equivalent N₂ decomposition temperature.     

Synthèse de nouveaux types de dérivés C-glycosyliques à partir de sucres acétyléniques ou de leurs équivalents synthétiques partiels

Synthesis of Novel Types of C-Glycosyl-derivatives from Acetylenic Sugars or Partial Synthetic Equivalents thereof The concept of synthetic equivalent is not unequivocal and, for example, α-fluoroenamines may behave in some cases as synthetic equivalents of ynamines and, in other situations, quite differently. Some uses of these α-fluoroenamines, ‘partial synthetic equivalents’ of ynamines, for the synthesis of C-glycosyl derivatives of coumarins, chromones, quinolines, quinolones, thietenes and isoxazoles are described. We also report the preparation of a series of mono- and diglycosylthiophenes by reacting HS^? with mono- and diglycosylbutadiynes. Acetylenic sugar derivatives have also been used for the synthesis of a diglycosylazaphosphorine and a spirooxolenone.     

Etude en RMN de l'Association des Sels de Lanthanides avec des Phénols; Application à la Détermination de Structure de Polyphénols Naturels

Interaction of lanthanide salts with phenols in DMSO solution was investigated as a tool for ¹H NMR structure determination in the field of naturally-occurring polyphenolic compounds. Intermolecular competition experiments evidenced reactivity differences with respect to the nature and position of substituents. Empirical rules of reactivity are suggested from which variations observed in the PMR chemical shifts on addition of lanthanide salts to natural polyphenols (flavones, xanthones) were rationalized.     

Obtention de phosphore élémentaire et de phosphures de nickel par électrolyse de solutions de pentoxyde de phosphore dans des bains à base de cryolithe

By electrolysis of cryolitic solutions of P₂O₅, elementary pure phosphorus is obtained on carbon cathode and Ni phosphides on Ni cathode. The most probable mechanism of phosphorus formation in these conditions seems to be the final dissociation of P₂O₅ in P⁵⁺ and O^2? and the primary electrodic discharge of these ions.