Spectrophotometric cerium

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

Measurement of Reaction Rates by Titrimetry. The rates of cerium(IV) consumption by each of Cr(C204)3 3, m-Cr(OH2)2(C204)2 and Cr(0H2)4C204+ were also measured by a direct titrimetric method. Solutions were prepared and mixed as for the spectrophotometric procedure. At appropriate times aliquots of the reactant solutions were quenched with known volumes of standard ferrous sulfate, and the excess ferrous ion was titrated potentiometrically with standard potassium dichromate,... 

Ciprofloxacin was determined in tablets and intravenous infusion solutions by an oxidative spectrophotometric method [15]. A yellow-orange complex was obtained upon reaction of ciprofloxacin with 5% ammonium sulfamate, 5 N H2S04, and 0.1 M cerium(IV) ammonium sulfate. The complex was extracted into CHC13, dried with anhydrous Na2S04, and measured at 345 nm within up to 4 h. Beer s law was obeyed over the range of 12-120 pg/mL, and the molar absorptivity was found to be 5090. 

Analysis. The heating value, ash content, and sulfur distribution of the raw and treated coals were determined according to ASTM procedures (7). Iron in the extracts of the raw and treated coals was determined by titration with a cerium (IV) solution. Iron in the residues from the acid extractions of the raw and treated coals was determined spectrophotometrically using ferrozine (20). The liquid extracts were analyzed for total sulfur (as sulfate) by ion chromatography after separation of the sulfate from nitrate on an alumina column (21). Nitrogen was determined in the raw and treated coal and in their nitric acid-extracted residues by a modified Kjeldahl method. 

In sulfuric acid, tetravalent cerium is more stable than in the other aqueous solutions (Figure 2). For this reason IN H2SO4 was chosen as the medium for spectrophotometric measurements. Nevertheless it was necessary to oxidize electrolytically all the reagents before the spectrophotometric measurements. This is illustrated by Figure 3 in which the optical densities vs. the cerium (IV) concentrations are plotted. 

The verification of Lamber Beer s law is shown in Figure 4. Organic solutions of cerium were prepared by extracting cerium (IV) from titrated aqueous solutions and standardized by beta counting of Ce tracer. Standardization curves were plotted from three values for further spectrophotometric determinations of cerium (IV). 

Procedure. Aqueous phases were prepared from samples of cerium (IV), cerium (III), berkelium, and acid and diluted by distilled water to the proper concentrations. Samples of cerium were chosen in order to obtain dijSerent cerium (IV)/cerium (III) ratios. The solutions were allowed to stand for six hours to reach the oxidation equilibrium. A 2 cc. sample of the solvent was added to the same volume of aqueous solution and mixed for 15 minutes. After separation by a centrifuge, samples of both phases were taken for the beta counting of berkelium and the spectrophotometric determination of cerium (IV). In addition, one aliquot of the loaded solvent was taken for determining the distribution coefficient of berkelium (IV). 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

Analytical Procedure. Determinations of G(Cem) were based on molar extinction coefficients for cerium (IV) and iron (III) in 0.4M sulfuric acid at 25 °C. of 5580 at 320 m/x and 2210 at 305 m/x, respectively. The validity of these molar extinction coefficients relative to each other was previously established (24) spectrophotometrically by oxidation of iron (III) by cerium (IV). For cerium (IV) analyses at other sulfuric acid concentrations, the dependence of the molar extinction coefficient for cerium(IV) on sulfuric acid concentration as reported by Boyle (5) was used. 

Irradiations were within a 60Co source (— 2000 curies) with a dose rate of about 1018 e.v. ml.-1 min. 1 in the ferrous sulfate dosimeter. Changes in cerium (IV) concentration were followed with a Cary recording spectrophotometer at 340 mfx. No detectable effect on measurements at 340 m[a could be attributed to coloration of the S 18-260 silica windows during irradiation. Therefore, irradiations and spectrophotometric measurements were made in the same cell. 

Unsaturated and hydroxylated triterpenes and steroids give colored products with aromatic aldehydes in strong mineral acids, with acetic anhydride in sulfuric acid, and with inorganic salts (cerium(IV) sulfate and antimony(III) chloride, for example) in an acidic solution. These reactions have been used as the basis for determination of saponins. The analysis of Ginseng radix (Panax ginseng, Araliaceae) in Pharmacopoeia Helvetica VII, for example, relies on reaction with glacial acetic acid/sulfuric acid and spectrophotometric determination at 520 nm of the red product. The jS-aescine component of horse chestnut (Aesculus hippocastanum, Hippocastan-aceae) saponin can be determined spectrophoto-metrically after treatment with a mixture of iron(III) chloride, acetic acid, and sulfuric acid. 

In the early days of vitamin Ki(20) discovery, colorimetric and UV-visible spectrophotometric methods were applied for identification and quantitative purposes. Also, the formation of fluorescent derivatives has been described. Other physicochemical methods include titration with cerium(IV) sulfate, polarogra-phy, microcoulometry, and phosphorimetry. These methods, however, have now been largely replaced by modern chromatographic techniques such as LC and to a lesser extent GC and TLC. 

Ionic strength and specific ion effects have been investigated in the oxidation of mandelic acid by cerium(iv) sulphate. Unlike the reaction in HCIO4 where there is spectrophotometric and kinetic evidence for complex formation, under these conditions there is a first-order rate dependence of both oxidant and reductant. The replacement of H+ by Li+, Na+, or K+ produces only a minor change in rate and has no effect on the activation parameters. Rate laws which are essentially similar have been established in the reactions with cyclohexane-1,4-diol cyclopentanone, and methyl isopropyl ketone. The enol form of the substrate is favoured as the active reagent in the latter two reactions. 

The temporal oscillating patterns of certain chemical intermediates have been observed only in a stirred BZ reaction system. Similar to cerium-catalyzed BZ reaction, the oscillation is occurred between colorless and yellow color at an assured time interval. There are some other important indicators where oscillations can be monitored due to the gradual color change, either direcdy in batch reactor [37, 38] or via spectrophotometric measurements [39, 40]. The most excellent illustration of oscillations manifested in batch reactors in the form of color variation of ferroin-catalyzed BZ reaction system. On the other hand, in some other reaction systems such as the manganese-catalyzed system and the cerium-catalyzed reaction, oscillations can be observed with the help of UV-visible spectrophotometer [41] where change in color might be monitored less distinctly. 

Thiophen Derivatives of Analytical Interest.—2-Thenoyltrifluoroacetone has maintained its position as a chelating agent in analytical chemistry. Papers describing its use in the extraction or determination of thorium, copper, europium, thallium, niobium, and molybdenum have appeared. The effect of copper(n) on the formation of monothenoyltri-fluoroacetonatoiron(iii) has been studied. The stability constants of some bivalent metal chelates of di-(2-thenoyl)methane have been determined. 3-Thianaphthenoyltrifluoroacetone has been proposed as a reagent for the spectrophotometric determination of iron(iii) and cerium(iv). The stabilities of metal chelates formed from derivatives of thiophen-2-aldehyde and of rare-earth carboxylates of thiophen-2-carboxylate have been studied. 

A method for the determination of fluorine in fluorinated polymers such as polytetrafluoroethylene (PTFE) is based on decomposition of the sample by oxygen flask combustion followed by spectrophotometric determination of the fluoride produced by a procedure involving the reaction of the cerium(III) complex of alizarin complexan (1,2-dihydroxy-anthraquinone-3-ylmethylamine N,N-diacetic acid). The blue colour of the fluoride-containing complex (maximum absorption, 565 nm) is completely distinguishable from either the yellow of the free dye (maximum absorption, 423 nm) or the red of its cerium(III) chelate (maximum absorption, 495 nm). 

The oxidation of tellurium(IV) by cerium(IV) in perchloric acid media has been studied in the range [H ] = 2-5 Although there is no variation with ionic strength, the reaction is retarded by one product, Ce(III), and accelerated by the other, Te(VI). Spectrophotometric evidence for a 1 1 complex between Ce(IV) and Te(IV) is confirmed by the first-order kinetic behavior of the oxidant but the order with respect to Te(IV) is fractional. 

Sultan, S. M., Y. A. M. Hassan, and K. E. E. Ibrahim. 1999. Sequential injection technique for automated titration Spectrophotometric assay of vitamin C in pharmaceutical products using cerium(IV) in sulfuric acid. Analyst 124 917-921. 

The phase portrait and the corresponding Poincare sections presented in the following are constructed using the usual time delay method (3 > from a single time series, namely the time variation of the cerium IV monitored spectrophotometrically at 360nm. 

The ceric-cerous sulfate dosimeter is a chemical dosimeter acting either as a routine dosimeter or as a reference standard dosimeter for the measurement of high dose levels (Matthews, 1982). A routine dosimeter is used in radiation processing facilities for dose mapping. A reference standard dosimeter is used to calibrate radiation fields and routine dosimeters. The dosimeter is based on the reduction of cerium(IV) to cerium(in) in an aqueous solution by radiation (Matthews, 1971). Doses in the range 0.5 to 50 kGy can be determined by conventional spectrophotometric analysis in the ultraviolet region, or by measuring the difference in the electrochemical potential between the irradiated and non-irradiated solutions in an electrochemical potentiometer (Matthews, 1972 Church et al., 1976). As most dosimeters, the... 

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