Catalytic spectrophotometric determination of trace amount of cerium(IV)

Based on a property that in dilute hydrochloric acid hydrogen peroxide oxidizes Ponceau S to fade and cerium(IV) has a catalytic effect on the reaction, a new spectrophotometric method was developed for the determination of trace cerium(IV). At 450 nm, the cerium(IV) concentration presents a good linear relationship over the range of 0.08?4 μg/mL with the fading degree ΔA. Its linear regression equation is ΔA = 0.0475c (μg/mL) + 0.0007, with a correlation coefficient of 0.9991. The detection limit of method is 0.05 μg/mL. The method has been successfully applied to the determination of cerium in water and molecular sieve samples with good results. The relative standard deviations of eleven determinations were 0.97?1.11 and 0.19?1.01%, respectively. The recoveries of standard additions were 99.4?99.9 and 99.2?101.0%, respectively. The reliability of this method was certified by parallel determination against the dibromo-p-chlorochlorophosphonazo spectrophotometry.     

Oxidative breakdown of polymeric plutonium(IV) hydroxide by cerium(IV)

The breakdown of polymeric plutonium(IV) hydroxide (plutonium colloid) by cerium(IV) has been studied spectrophotometrically by monitoring the formation of plutonium(VI). Reaction rate variations were studied with changes in cerium(IV), acid and plutonium colloid concentrations. A reaction mechanism involving the formation of [Ce₂O(OH)₂]⁴⁺ and its reaction with the polymer surface to produce two plutonium(V) ions is postulated to explain the observed kinetic data, in particular the maximum in the reaction rate at around 0.3 M nitric acid.     

Capillary electrochromatography of peptides on microfabricated poly(dimethylsiloxane) chips modified by cerium(IV)-catalyzed polymerization

Ceramides are important intracellular second messengers that play a role in the regulation of cell growth, differentiation and programmed cell death. Qualitative and quantitative analysis of these second messengers requires sensitive and specific analytical methods to detect endogenous levels of individual ceramide species and to differentiate between them. Nine synthetic ceramides were separated by liquid chromatography coupled to tandem mass spectrometry on a C18 bonded silica column. The lipids were eluted in gradient elution mode using a mixture of water, acetonitrile and 2-propanol as mobile phase. They were detected by reaction monitoring performed on positive ion electrospray generated ions. Collision-induced fragmentations conducted on ceramides produced a well characteristic product ion at m/z 264, making multiple reaction monitoring (MRM) well suited for various ceramides quantitative measurements. After optimization of the extraction step, the proposed methodology was able to identify and quantify different ceramide species issued from human cancer cells. The method could be validated for C16, C18 and C20 ceramides, quantified at the nanogram level. The validation exhibits good results with respect to linearity, accuracy and precision.     

Simultaneous spectrofluorimetric determination of cerium(III) and cerium(IV) by flow injection analysis

Cerium(III) (1–100 μg l^?1) is determined by injection into a carrier stream of hydrochloric, perchloric or sulphuric acid, and monitoring its native fluorescence. Cerium(IV) can be determined similarly by incorporating a zinc reductor minicolumn into the system. Splitting the injection sample so that only part passes through the reductor, and the remainder by-passes it, allows total cerium and cerium(III) to be detected from the two sequential fluorescence peaks obtained.     

Determination of cerium(III) and cerium(IV) in nanodisperse ceria by chemical methods

Percentages of different valence cerium species have been determined in powdery samples, redispersible compositions, and aqueous sols of nanodisperse ceria prepared from cerium(IV) and cerium(III) salts by various methods with or without organic stabilizers. Cerium(III) is shown to be virtually absent in nearly all of the CeO₂ samples studied. Organic stabilizers are shown to be capable of reducing cerium(IV) in aqueous CeO₂ sols.     

Iodometric estimation of cerium(IV) by arsenious oxide

Summary Determination of cerium(IV), depending upon its reduction to cerium-(III) by KI and titration of the liberated iodine with standard arsenious oxide solution in a suitably adjusted p_H range, is described.Sincere thanks of the author are due to Professor S. S. Joshi for research facilities.     

Phosphoester hydrolysis by cerium(IV)-thiacalix[4]arene complexes and its application to immunoassay

Thiacalix[4]arenetetrasulfonate was treated with Ce(IV) in water at pH 9.5 to give novel phosphoester-hydrolyzing complexes. The dinuclear Ce(IV) complex promoted the hydrolysis of p-nitrophenyl phosphate with a turnover frequency of 6.8 h⁻¹ at 50 °C, showing fourfold higher activity than the mononuclear complex. The dinuclear complex was readily immobilized onto an antibody by simply mixing them in water, hence its phosphatase-like activity was applied to the color-developing reaction in immunoassay. The model assay using an antibody labeled with the dinuclear complex allowed the detection of as little as 10 ng mL⁻¹ of a tumor marker, Bence–Jones protein, in a 96-well microtiter plate format. Analysis of urine for Bence–Jones protein was performed by the proposed method.     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tellurium(IV) by cerium(IV)

The reaction is zero order in cerium(IV), fractional order in tellurium(IV) and first oder in ruthenium(III). While the ionic strength has no effect, the rate increases with increasing [H⁺], and decreases with increasing [HSO ₄ ^– ]. H and S are 54.4 kJ mol^–1 and –60.3 JK^–1 mol^–1, respectively. A suitable mechanism is proposed.

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(IV), (IV) (III). , [H⁺] [HSO ₄ ^– ]. H S 54,4 ^–1 –60,3 ·^–1·^–1, . .

     

Indirect spectrophotometric determination of cerium(IV)

A simple and very fast photometric method for the determination of trace levels of cerium(IV) has been developed. Use has been made of the reaction in which iron (II), on oxidation with cerium(IV), gives iron(III) which is complexed with tiron, in acidic medium, to form a stable blue color, the intensity of which is in direct proportion to the amount of cerium(IV) originally present in the sample solution. In addition, the method has a wide range of determination and reasonable sensitivity, and it avoids both temperature control and the tedious extraction step.     

Kinetics and mechanism of osmium(VIII) catalyzed oxidation of tellurium(IV) by cerium(IV)

The reaction is first order in substrate and catalyst and zero order in cerium(IV). The rate decreases with increasing [H⁺] as well as with increasing ionic strength. H and S have been found to be 44.8 kJ mol^–1 and 161.8 JK^–1 mol^–1 respectively. A mechanism is proposed.

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(IV). [H⁺], . , H S 44,8 ·^–1 161,8 ·^–1–1, . .

     

Iridium(III) catalyzed oxidation of cyclic ketones by cerium(IV)

IrCl₃which is considered to be a sluggish catalyst in alkaline media, was found to surpass the catalytic efficiency of even osmium and ruthenium in acidic media in the oxidation of cyclopentanone and 2-methylcyclohexanone by cerium(IV) sulphate in aqueous sulphuric acid medium. It was observed that the order of the reaction shows direct proportionality with respect to low concentrations of the oxidant and alcohols, but tends to become independent of concentration at higher concentrations. On increasing the concentrations of externally added Cl^-, H⁺ and Ce^IIIions, the rate of the reaction decreases sharply initially but the decrease in rate becomes less prominent as their concentration is increased. The rate of reaction is directly proportional with respect to IrCl₃concentrations. Kinetic data suggest that the production of Ce^III ion occurs before the rate-determining step. Parameters such as the energy of activation, free energy of activation and entropy data collected at five different temperatures suggest that cyclopentanone forms the activated complex more easily.     

On the determination of cerium(IV) by iodate and bromate

Analytical and Bioanalytical Chemistry - Determination of cerium(IV), based upon its reduction by a measured excess of KSCN solution and titration of the excess against standard iodate or bromate,...     

Extraction of trace amounts of cerium(III) by oxides of amines and its separation from cerium(IV)

The solvent extraction of cerium(III) from nitric, hydrochloric and sulphuric acid solutions by 4-(5-nonyl)pyridine oxide and trioctylamine oxide in xylene has been studied. The influence of the concentration of the solvents and salting-out agents is described. From the results of partition experiments attempts have been made to deduce the nature of the extracted species. The investigation shows that cerium(III) can be separated from cerium(IV) from very dilute solutions of mineral acids and also from moderate nitric acid media.     

Thermogravimetric studies of dipyridinium complexes of cerium(IV), thorium(IV) and zirconium(IV)

The TG curves of dipyridinium complexes of Ce(IV), Th(IV) and Zr(IV) have been reported. The mode of decomposition of the cerium and thorium complexes is broadly comparable but the decomposition of Zr complex shows some variation.     

Unprecedented examples of heterobimetallic cerium(IV) disiloxanediolates

The first disiloxanediolate complexes of cerium(IV) are reported. Starting from the readily available precursor ((t)BuO)(3)Ce(IV)(NO(3))(THF)(2) (1), we prepared the novel heterobimetallic compounds [{(Ph(2)SiO)(2)O}{K(THF)(2)}](2)Ce(O(t)Bu)(2) (2) and [{(Ph(2)SiO)(2)O}(2){(DME)-KO(t)Bu}{(Ph(2)SiO(2))K}Ce](2) (3) and structurally characterized them by X-ray diffraction.     

Spectrofluorimetric determination of pharmaceutical compounds with the cerium(IV)—cerium(III) system

The compounds to be determined are oxidised by cerium(IV). The concentration of cerium(III) formed is measured spectrofluorimetrically. The method has been used both in solution and, by fluorodensitometry, on t.l.c. plates. Detection limits of some substances are 15 ng ml^-1 for the solution method and 5 ng per spot for the t.l.c. method.     

Oxidation of ketones by cerium(IV) in presence of iridium(III) chloride

Kinetic data, in iridium(III) chloride catalyzed oxidation of ethyl methyl ketone (EMK) and methyl propyl ketone (MPK) by cerium(IV) perchlorate in aqueous perchloric acid medium, suggest the formation of complex C₁ between cerium(IV) and organic substrate in the first equilibrium step, which in turn gives rise to another complex C₂ with the catalyst. This second complex in the rate-determining step gives rise to the intermediate products. Interestingly IrCl_3, which is considered to be a sluggish catalyst in alkaline media, was found to surpass the catalytic efficiency of even osmium and ruthenium in acidic media. Rate decreases in the beginning at low acid concentrations, but after reaching to a minimum it becomes directly proportional to acid concentrations. Probably on increasing the acid concentrations hydrolyzed species of ceric perchlorate gradually converts into the un-hydrolyzed species, which then accelerates the rate at higher [H⁺], resulting in the observed peculiar effect of hydrogen ions on the rate. Initial concentrations of cerium(IV) and acid determine the extent of reduction of cerium(IV) by water. Order of the reaction shows direct proportionality with respect to the oxidant and ketones at their low concentrations, but tends to become zeroth order at their higher concentrations. Rate of the reaction shows direct proportionality with respect to [IrCl₃] while change in ionic strength of the medium does not affect the reaction velocity. Parameters such as the energy of activation, free energy of activation and entropy data suggest that methyl propyl ketone forms the activated complex more easily compared to ethyl methyl ketone.