Search results for "element"
showing 10 items of 13601 documents
Literature survey of on-line elemental speciation in aqueous solutions.
2001
The literature about the on-line speciation in water has been comprehensively studied. Critical examination of this subject reveals that a great deal of work has been performed in this area for inorganic metal species and some organic compounds. The topic studied mainly includes the speciation of chromium, selenium, copper, arsenic, lead, cadmium, mercury, iron, aluminium, nickel, tin, antimony, phosphorus, nitrogen and others. The present literature survey includes also comments about the possibilities and problems of speciation as a function of analytical steps, general strategies involved and methods proposed in the literature for each element or a series of elements.
Comparison of ultrasound-assisted extraction, microwave-assisted acid leaching and reflux for the determination of arsenic, cadmium and copper in con…
2002
Extraction methods for the determination of arsenic, cadmium, and copper in contaminated soil samples by Zeeman effect electrothermal atomic absorption spectrometry have been compared. The determination of cadmium and copper in ultrasound-assisted aqua regia extracts of contaminated soil SRMs by ETAAS, using a mixture of NH4H2PO4 and Mg(NO3)2, for cadmium, and a mixture of Pd and Mg(NO3)2, for copper, as a matrix modifier, was carried out with high accuracy and precision (RSD < 5.1%). The analysis of SRM 2711 failed to obtain the certified concentrations of Cd and Cu by microwave and reflux methods, respectively. The determination of arsenic was performed successfully in low chloride concen…
Determination of Cd, Co, Cu, Fe, Pb, Mn, Ni and Zn in diets: Development of a method
1991
A method useful for the determination of cadmium, cobalt, copper, iron, lead, manganese, nickel and zinc in diets is described. Organic matter is destroyed applying a wet procedure, and element content is measured by flame atomic absorption spectroscopy (FAAS) in the case of copper, iron, manganese, nickel and zinc, and by graphite furnace (GF-AAS) in the case of cadmium, cobalt and lead. The matrix interference study is carried out. Values found for linearity, detection and quantitation limits as well as accuracy show that the described method is useful to determine the elements taken into account at usual levels in diets.
The influence of cerium to urea preparation ratio of nanocrystalline ceria catalysts for the total oxidation of naphthalene
2008
The influence of cerium salt/urea ratio on the activity of nanocrystalline ceria catalysts prepared by homogeneous precipitation with urea for the complete oxidation of naphthalene has been evaluated. Ceria catalysts were prepared from five different cerium salt/urea ratios (2:1, 1:1, 1:2, 1:3 and 1:4). Catalyst characterization (by BET, XRD and TPR) only revealed subtle differences in the characteristics of these catalysts with cerium salt to urea ratio. However, Raman and scanning electron microscopy (SEM) results indicated differences in the oxygen defect concentration (FWHM of Raman band) and morphology of the catalysts with variation of the preparation ratio. Catalysts prepared with 2:…
Nanopore charge inversion and current-voltage curves in mixtures of asymmetric electrolytes
2018
[EN] We consider the screening of the negative charges (carboxylic acid groups) fixed on the surface of a conical-shaped track-etched nanopore by divalent magnesium (Mg2+) and trivalent lanthanum (La3+). The experimental current (I)-voltage (V) curves and current rectification ratios allow discussing fundamental questions about the overcompensation of spatially-fixed charges by multivalent ions over nanoscale volumes. The effects of charge inversion or reversal on nanopore transport are discussed in mixtures of asymmetric electrolytes (LaCl3 and MgCl2 with KCl). In particular, pore charge inversion is demonstrated for La3+ as well as for mixtures of this trivalent ion at low concentrations …
A Review on Molybdenum Determination in Solid Geological Samples
2007
This review highlights the necessity for the development of proper sampling and storage, fast pretreatment methodology followed by highly sensitive detection for the determination of molybdenum in geological samples. Distribution of concentration and chemical speciation of molybdenum analysis in solid geological matrices have also been discussed.
Gravimetric determination of palladium with biguanide sulfate
1986
Abstract Biguanides are interesting reagents for the determination of palladium owing to their solubility, chemical resistance, and selectivity in moderately acidic solutions. A procedure for the gravimetric determination of palladium(II) in the form of Pd(HL)2SO4, where HL = biguanide, is proposed and the conditions of precipitation, treatment of the precipitate, precision, accuracy, and selectivity of the procedure are discussed.
Unprecedented Palladium-Catalyzed Cross-Coupling Reaction of α-Bromo Sulfoxides with Boronic Acids
2003
[reaction: see text] A new Suzuki-type palladium-catalyzed reaction of boronic acids with alpha-bromo sulfoxides has been developed using a protocol similar to the well-documented reaction of boronic acids with aryl halides. Both cross-coupling and homocoupling processes were observed. The best yields in cross-coupling products were obtained when the presence of oxygen was carefully excluded using degassed solvents. The oxidative addition palladium complex intermediate could be isolated and characterized by X-ray single-crystal diffraction.
Uranium speciation in plants
2002
The chemical characterization of the radionuclide species is essential for a reliable assessment of the migration of radionuclides and heavy metals into the geological and biological environment on the load pathway soil - plant - animal - human. Only a few is known about the speciation of uranium in plants. Therefore we investigate the change of speciation during the transfer of uranium from initial solution into plant. Various plants (lupins, dandelion e.g.) were grown in an agricultural test field and in the laboratory on contaminated soils (up to concentration of 1g U/kg soil) and as hydroponics in the uranium containing solutions (uranium concentration: 10-5 M - 10-2 M, pH: 3 - 8). For …
Pd and PdAu on mesoporous silica for methane oxidation: Effect of SO2
2007
Abstract Palladium and gold–palladium catalysts supported on mesoporous silica were prepared by incipient wetness impregnation. They were characterized by XPS, XRD, BET, and FTIR acidity measurements. The activity was tested in the oxidation of methane under lean conditions. The effect of adding SO 2 to the reactant mixture was investigated. Test reactions were consecutively performed to evaluate the thermal stability and poisoning reversibility. The palladium catalyst performed quite well in terms of the light-off temperature ( T 50 300 °C) and SO 2 tolerance. Moreover, the activity, which decreased after a night treatment in SO 2 at 350 °C, was completely recovered in subsequent cycles. …