A kinetic-catalytic method with repeated addition of one reactant — the determination of manganese, iodide, urease and cadmium

The use of a new kinetic-catalytic method with repeated addition of one reactant in the same system is described. The determination of manganese (periodate—malachite green; photometric observation), iodide (cerium(IV)—arsenic(III); potentiometric observation) and urease (hydrolytic splitting of urea; potentiometric observation) serves to illustrate the procedure.     

Dosage electrochimique du cobalt : II. Applications aux Aciers à Faible ou à Moyenne Teneurs

Electrochemical determination of cobalt. Part I. Studies of current—voltage curves of the cobalt(III)/cobalt(II) system in picolinic acid mediaAs a preliminary to the development of electrochemical determinations of cobalt in steels, current—voltage curves at a platinum electrode were studied for the systems coblt(III)/cobalt(II) and iron(III)/iron(II) in media containing picolinic acid as complexing agent. Iron(III) oxidizes cobalt(II) in this complexmg medium, and the iron-(II) formed can be determined by an oxidant such as cerium(IV).     

N-oxides of 4-(5-nonyl)pyridine and trioctylamine as extractants for cerium(IV) and its separation from thorium(IV)

Trace level cerium has been oxidized to the quadrivalent state with potassium dichromate and shown to be preferentially extracted from very dilute mineral acid solutions and also from moderate nitric acid media by 0.1M solutions of 4-(5-nonyl)pyridine oxide and trioctylamine oxide dissolved in xylene. The dependence of extraction on the type of N-oxide, acid concentration and the N-oxide concentration has been investigated. The influence of the concentration of salting-out agents is described. Separation factors for a number of metal ions relative to cerium(IV) are reported for 0.1 M 4-(5-nonyl)pyridine oxide/xylene-0.1M sulphuric acid system. The ratio of the D for Ce(IV) to that of Ce(III) is greater than 10⁵, and the D for Ce(IV) is much greater than that for thorium(IV). Separation of cerium(IV) from thorium has been achieved from 0.1M sulphuric acid solutions using 0.1M 4-(5-nonyl)pyridine oxide/xylene as an extractant.     

Solvent extraction and photometric determination of a microgram of cerium with N-p-tolyl-p-chlorobenzohydroxamic acid

A spectrophotometric method for determination of a microgram quantity of cerium with N-p-tolyl-p-chlorobenzohydroxamic acid is described. The orange-red-colored complex is extracted from chloroform at pH 9 which absorbs between 460 and 465 nm. Beer's law is obeyed at this wavelength. A clean-cut separation from many commonly occurring metal ions is easily accomplished. The system obeys Beer's law within the range of 0.5–28 ppm of cerium(IV). The molar absorptivity of cerium-N-p-tolyl-p-chlorobenzohydroxamic acid complex is 4.5 × 10³ liters mol^?1 cm^?1.     

Titrimetric and spectrophotometric methods for the determination of cerium(IV) in aqueous solution

A titrimetric and spectrophotometric methods for cerium(IV) determination have worked out. The first method relies upon the treatment of cerium(IV) solution with an excessive amount of iodide; the liberated iodine is extracted into chloroform, then reduced to iodide. The latter is iodometrically determined after 6- or 36-fold amplification. The spectropho-tometric finish is based upon the reaction of the titled ion with iron(II), in the presence of hexacyanoferrate(II), to form an intense prussian blue color suitable for the trace determination of cerium(IV) ion.     

Electrochemical studies of technetium at a mercury electrode

The electrochemistry of technetium was studied by polarography, cyclic voltammetry and coulometry in chloride and sulfate media as a function of pH in the range 1.5–13. Compounds of Tc(III) and Tc(IV) are produced by reduction of pertechnetate, and the system Tc(III)/Tc(IV) was investigated in acidic media. The potential—acidity diagram of technetium is described for two total pertechnetate concentrations. Evidence for the dismutation of Tc(III) below pH 4 is discussed.     

Technetium chemistry in a novel group actinide extraction process

A newly developed method for advanced reprocessing of used nuclear fuel is the Group ActiNide EXtraction (GANEX) process. It is a liquid–liquid extraction process that aims at extracting all the actinides as a group from dissolved used nuclear fuel. This extraction can either be performed after a removal of the bulk uranium or directly on the dissolution liquor. At Chalmers University of Technology in Sweden a solvent that utilizes tributyl-phosphate (TBP) and a molecule from the bis-triazine bipyridine (BTBP) class of ligands dissolved in cyclohexanone has been developed for the use in a GANEX process. Previously the system has not been tested with the presence of technetium that is one of the major fission products. Technetium is often considered a problem within reprocessing since it has a chemical behaviour that differs from most other elements in the spent fuel. Therefore, a special emphasis was put on the investigation of technetium in the selected GANEX system. It was shown that technetium is readily extracted by the GANEX solvent and that cyclohexanone is the main extractant when no other metals were present in the system. It was also found that the presence of uranium decreased the overall technetium extraction despite a slight co-extraction with TBP, while irradiation of the GANEX solvent to large doses (>1 MGy) increased its technetium extraction capability. It was also discovered that an increased nitrate concentration in the aqueous phase and an addition of other fission products both inhibited the technetium extraction even though fission product loading most likely changed the extraction mechanism to co-extraction by BTBP.     

Studies on the Radical Cyclization of 3‐Oxopropanenitriles and Alkenes with Cerium(IV) Ammonium Nitrate in Ether Solvents

The radical cyclization of 3‐oxopropanenitriles 1a – 1e and alkenes 2a – 2g with cerium(IV) ammonium nitrate (CAN) in ether solvents was investigated (Tables 1 and 2). In the optimization study, 1,3‐dioxolane, 1,4‐dioxane, 1,2‐dimethoxyethane, Et₂O, and THF were used as ether‐based solvents, and the latter was found to be the most effective solvent in radical cyclizations mediated by cerium(IV). This system (cerium(IV)/THF) was applied to cyclizations of various 3‐oxopropanenitriles and 1,3‐dicarbonyl compounds with alkenes resulting in the formation of 4,5‐dihydrofurans in high yields (Table 2 and Scheme 2). The results of the cerium(IV)/THF radical cyclization were compared with those obtained with manganese(III) acetate/AcOH; the cerium(IV)/THF system turned out to be much more efficient.     

Surface characterization of growth process for cerium conversion coating on magnesium alloy and its anticorrosion mechanism

Cerium conversion coating is successfully deposited on magnesium alloy AZ31 for corrosion protection. Deposition time on the influence of cerium conversion coating morphology, composition, and electrochemical properties has been investigated in detail. Morphological observation reveals that the cerium conversion coating is a porous agglomerate nanostructure. XPS indicates that the coating exhibits a time‐dependent ingredient. Moreover, the coating is considered as a combination of magnesium oxide/hydroxide and cerium (III) and (IV) oxides/hydroxides. The results of electrochemical impedance spectroscopy indicate that the anticorrosion coating exhibits the best properties during deposition of 5 min. In view of the analysis, the anticorrosion mechanism is pioneered proposed because of the formation of H‐bonding layer, which forms a reasonable barrier to Cl^? ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Spot detection of cerium and cobalt

Summary Sulphosalicylic acid reacts with cerium(IV) at p_H 11±0.5 to give a redbrown complex. With cerium(III) the reaction proceeds only slowly but is markedly accelerated in the presence of cobalt(II). 0.7 g of cerium, and based on its catalytic action, 0.03 g of cobalt can be detected on a spot plate.

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Zusammenfassung Sulfosalicylsäure bildet mit Cer(IV) bei p_H 11±0,5 einen rotbraun gefärbten Komplex. Mit Cer(III) verläuft die Reaktion nur langsam, wird aber durch Gegenwart von Kobalt(II) beschleunigt. Noch 0,7 g Ce und — auf Grund der Katalyse — 0,03 g Co können auf der Tüpfelplatte nachgewiesen werden.

     

Self-assembly of cerium compound nanopetals via a hydrothermal process: Synthesis, formation mechanism and properties

Nanopetals of cerium hydroxycarbonate have been synthesized via a controlled hydrothermal process in a mixed water-ethanol medium. Electron microscopy indicates that each microsized flower consists of tens to hundreds of cerium hydroxycarbonate nanopetals. These nanopetals have a very large aspect ratio: a width as large as 10 μm, with a thickness as thin as 10 nm. The formation of the cerium compound depends strongly on the composition of the precursors, and is attributed to the favored ethanol oxidation by Ce(IV) ions over Ce(IV) hydrolysis process. Raman studies showed that microflower CeO₂ preferentially stabilizes O₂ as a peroxide species on its surface for CO oxidation.     

Spectrophotometric determination of cerium(IV) with tetraethylenepentaamineheptaacetic acid (TPHA)

Tetraethylenepentaamineheptaacetic acid (TPHA) combines with cerium(IV) to form an intensely yellow chelate having a molar absorptivity of 4.5 × 10⁴ mol⁻¹ · cm⁻¹ · liter at 304 nm. The chelate contains 1 mol of TPHA coordinated to a cerium(IV) atom. Beer's law is followed from 0.05 to 0.5 ppm cerium (1.00-cm cells). Of many ions tested at the 1-ppm level and the 100-ppm concentration, only iron(III) produces little interference.     

A New Spectrophotometric Method for the Determination of Cerium Using Leuco Disulphine Blue

A new, simple, highly sensitive spectrophotometric method for the determination of trace amounts of cerium(IV) is described. The method is based on the oxidation of leuco disulphine blue (LDSB) to its blue form of disulphine blue by Ce(IV) in a sulfuric acid medium (pH 1.3–3.0); the absorbance of the formed dye is measured in an acetate buffer medium (pH 3.0–4.8) at 635 nm. The color system obeys Beer's law in the concentration range from 0.5 to 5.5 g mL^–1 cerium with a molar absorptivity of 1.75 × 10⁴ L mol^–1 cm^–1 and a Sandell's sensitivity of 0.008 g cm^–2. All variables were studied in order to optimize the reaction conditions. The developed method has been successfully applied to the determination of cerium in high purity rare-earth oxides, soil, natural water, plant tissue, human hair, and rock samples.     

Synergistic extraction and separation studies of uranium(VI)

A method is described for the extractive separation and spectrophotometric determination of uranium(VI) from an aqueous solution of pH 5.0–7.0 using benzoylacetone (bzac) and pyridine (py) dissolved in toluene as extractants. The extracted species are UO₂(bzac(₂·2py. The method provides separation of uranium(VI) from lanthanum(III), samarium(III), neodymium(III), cerium(III) and thorium(IV). The method is precise, accurate, fast and selective.     

Rapid spectrophotometric determination of cerium(IV), arsenic(III), and nitrite with perphenazine

Perphenazine dihydrochloride, PPN, is proposed as a new reagent for the spectrophotometric determination of cerium(IV), arsenic(III), and nitrite. The reagent forms a red-colored species with cerium(IV) instantaneously in 3.5–5.5 M phosphoric acid medium. The red species exhibits maximum absorbance at 516 nm. A 15-fold molar excess of PPN is necessary for the full development of the color intensity. Beer's law is obeyed over the cerium concentration range 0.4–20 ppm and Sandell's sensitivity is found to be 0.016 μg/ cm². The effects of acidity, time, order of addition of reagents, temperature, reagent concentration, and diverse ions are reported. The proposed method offers the advantages of good sensitivity, simplicity, rapidity, selectivity, and a wider range of determination without the need for heating or extraction. Arsenic(III) and nitrite are also indirectly determined. The method is extended to the determination of cerium content in synthetic mixture corresponding to misch metal.     

Tellurites of some s–f elements: Synthesis, X-ray diffraction, and electrophysical properties

A possibility of solid-phase synthesis of new cerium double tellurites with s-elements from the oxides of cerium(IV), tellurium(IV) and magnesium (calcium, strontium) carbonates was demonstrated. It was determined by the X-ray diffraction method that the magnesium-cerium tellurite crystallizes in a cubic system, while calcium-cerium and strontium-cerium tellurites crystallize in the tetragonal crystal system.The temperature dependence of the electrical resistance of these compounds in the range of 300?C600 K was measured. The plots include sharp anomalous jumps due probably to the phase transitions of type II.     

Kinetic Determination of Iodide by the Sandell–Kolthoff Reaction Using Diphenylamine-4-Sulfonic Acid

The iodide-catalyzed reaction between arsenic(III) and cerium(IV) (Sandell–Kolthoff reaction) stopped by the addition of diphenylamine-4-sulfonic acid was used for the development of a sensitive kinetic procedure for determining iodides with a detection limit of 2 ng/mL. It was found that the developed procedure is suitable for the determination of total iodine in foodstuffs.     

Oxidation of cerium(III) to cerium(IV) using a mixture of hot concentrated perchloric and sulfuric acids

The oxidation of cerium(III) to cerium(IV) using a hot concentrated mixture of perchloric and sulfuric acids is shown to be quantitative Optimum conditions for the oxidation are described Complete removal of chlorine, an interfering decomposition product of boiling perchloric acid, is achieved by purging the concentrated acid solution with nitrogen before dilution with water The presence of sulfuric acid is essentral, the chief role of sulfuric acid apparently being to stabihze the cerium(IV) as a sulfatocerate complex.     

Spectrophotometric determination of cerium(IV) using a phenothiazine derivative.

A simple, rapid and sensitive spectrophotometric method has been proposed for the determination of cerium(IV) using a phenothiazine derivative, propionyl promazine phosphate (PPP). This method is based on the formation of a red-colored radical cation upon a reaction of PPP with cerium(IV) in a phosphoric acid medium having maximum absorbance at 513 nm. Beer's law is valid over the concentration range of 1-11 microg/ml with a Sandell's sensitivity value of 16.14 ng/cm2. The proposed method has been successfully applied to the analysis of magnesium-base cerium alloys and synthetic mixtures corresponding to various cerium alloys. Other phenothiazine derivatives viz. butaperazine dimaleate and propericiazine were also used for the determination of cerium(IV).     

Ion exchange studies of U(VI), Th(IV), Pu(IV) and Eu(III) on a macroreticular resin in TBP-Shell Sol-T solutions

Ion exchange studies of uranium(VI), thorium(IV), plutonium(IV) and europium(III) ions on a macroreticular cation exchange resin, Amberlyst A-15, from solutions of 30% and 5% TBP—Shell Sol-T have been carried out. The metal ions were extracted into TBP Shell Sol-T phase from 8M NH₄NO₃ at different nitric acid concentrations. Ion exchange distribution ratios as a function of organic phase acidity of 30% and 5% TBP have been computed. Separation factors computed from the observed Kd values are plotted as a function of organic phase acidity.