Determination of Dy(III) in the presence of Tb(III) using time-resolved luminescence

We have measured the relative luminescence quantum yields and luminescence lifetimes of Tb(III) and Dy(III) ions in complexes with pyrazole-5-carboxylic acids. Based on study of the time-resolved luminescence spectra of Tb(III) and Dy(III) complexes with 3-(6-benzodioxanyl)pyrazole-5-carboxylic acid, we have demonstrated the possibility in principle of determining Dy(III) in the presence of Tb(III) by separating the short-lived component of the luminescence of dysprosium, despite the practically complete overlap of the analytical bands of dysprosium by the terbium bands. This method was used to determine Dy(III) in luminescent materials: scandium borates doped with terbium and dysprosium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 327–331, May–June, 2007.     

Simultaneous determination of aluminum (III) and iron (III) by first-derivative spectrophotometry in alloys

A highly sensitive and selective first-derivative spectrophotometric method has been developed for the determination of aluminum and iron in mixtures. The method is based on the formation of the binary complexes of aluminum and iron with Alizarin yellow R (AYR) 5-[4-nitrophenylazo]salicylic acid at pH 2.0 with molar absorptivity of 1.1∙10⁴ l⋅mol^–1⋅cm^–1. A zero-crossing technique is found suitable for the direct measurement of the first derivative value at the specified wavelength, so aluminum and iron were thus determined in the ranges 1.3–5.4 μg/ml and 1.1–8.3 μg/ml, respectively, in the presence of both components. The detection limits were found to be 1.4 ng/ml for aluminum and 2.8 ng/ml for iron. The relative standard deviations were in all cases less than 1.5%. The proposed method was successfully applied for the simultaneous determination of aluminum and iron in certified reference aluminum samples.     

Determination of trace iron (II) and molybdenum (VI) in ground water by pyrocatechol resin-phase spectrophotometry]

In weak acid medium (pH 6.20), Fe(III) and Mo(VI) can form colored complexes with pyrocatechol and quantitatively adsorbed on 717 strong base anion exchange resin. The apparent molar absorption coefficients of resin phase are epsilon = 4.1 x 10(4) L/(mol x cm) at 520 nm for Fe(III) and epsilon = 9.0 x 10(4) L/(mol x cm) at 400 nm for Mo(VI). Beer's law is obeyed for Fe (III) and Mo(VI) in the range of 0-2.2 mg x L(-1) and 0-1.6 mg x L(-1). The method has been applied to the determination of trace Fe(III) and Mo(VI) in ground water. The relative standard deviations are 3.3% and 3.2%, respectively.     

EPR studies of weakly coupled oxomolybdenum (V) and low-spin iron (III) porphyrin centers

Novel compounds containing twoS=1/2 coupled spin centers (Mo(V) and low spin Fe(III) have been investigated in detail by X- and Q-band EPR spectroscopy, spectral simulation and molecular modelling calculations. For one system with a Mo?Fe distance of ≈9.4 Å the dominant dipolar coupling allows distinction among structures that are consistent with molecular modelling calculations. For the second system with a Mo?Fe of ≈ 7.9 Å the exchange interaction is dominant (0.5 <J < 3.0 GHz). These coupled systems are preliminary benchmarks for using EPR to investigate the Mo?Fe interaction in sulfite oxidase.     

An EXAFS spectroscopic study of Am(III) complexation with lactate

The pH dependence (1–7) of Am(III) complexation with lactate in aqueous solution is studied using extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. Structural data (coordination numbers, Am—O and Am—C distances) of the formed Am(III)–lactate species are determined from the raw k³‐weighted Am L_III‐edge EXAFS spectra. Between pH 1 and pH 6, Am(III) speciation shifts continuously towards complexed species with increasing pH. At higher pH, the amount of complexed species decreases due to formation of hydroxo species. The coordination numbers and distances (3.41–3.43 Å) of the coordinating carbon atoms clearly point out that lactate is bound `side‐on' to Am(III) through both the carboxylic and the α‐hydroxy function of lactate. The experimentally determined coordination numbers are compared with speciation calculations on the basis of tabulated thermodynamic stability constants. Both EXAFS data and thermodynamic modelling are in very good agreement. The EXAFS spectra are also analyzed by iterative transformation factor analysis to further verify the determined Am(III) speciation and the used structural model.     

A study of the thermal decomposition of iron(II) and iron(III) rubidium oxalates using the Mössbauer effect

The thermal decompositions of Rb₃Fe(ox)₃ 4 H₂O and Rb₂Fe(ox)₂ 6 H₂O have been studied using Mössbauer spectroscopy and thermal analysis methods (TGA, DSC). It is shown that after dehydration, the ferric complex is reduced into a ferrous compound, with a large quadrupole splitting (3.84 mm/s), which corresponds to the anhydrous form of Rb₂Fe(ox)₂ 6 H₂O.     

Determination of As (III) and As(V) in sea water by hydride generation atomic fluorescence spectrometry

The present paper reports a method based on intermittent flow injection (FI) hydride generation (HG) combined with atomic fluorescence spectrometry (AFS) detection for the determination of As in sea water. Experimental conditions for FI-HG were optimized. 5.0% hydrochloric acid-0.1 mol x L(-1) citric acid solution was selected as the carrier flow as well as the sample medium, and 2% KBH4-0. 5% KOH was used as the reductant. An argon gas flow was used for carrying the generated arsine to the Ar-H2 flame for atomization. Organic species of arsenic cannot be generated arsine under the selected conditions. The real sea water samples collected at Zhanqiao seashore in Qingdao and more than 30 other areas were analyzed under optimized working conditions, and experiments verified that the determination of As(III) and As(V) could approximately assess the As pollution for marine water while organic arsenic in natural sea water was so slight that could be neglected in case large amount of samples should be analyzed.     

Magnetic properties of calcium-silicates (diopside and gehlenite) doped with iron (III)

The incorporation of Fe³⁺ cations into some Ca-silicates (diopside, gehlenite), substituting for alkali earths of different valencies and in differently coordinated lattice positions, will give rise to considerable lattice disorder. It is shown that this will result in special magnetization properties of these silicates.     

The pH dependence of Am(III) complexation with acetate: an EXAFS study

The complexation of acetate with Am(III) is studied as a function of the pH (1–6) by extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. The molecular structure of the Am(III)–acetate complexes (coordination numbers, oxygen and carbon distances) is determined from the raw k³‐weighted Am L_III‐edge EXAFS spectra. The results show a continuous shift of Am(III) speciation with increasing pH value towards the complexed species. Furthermore, it is verified that acetate coordinates in a bidentate coordination mode to Am(III) (Am—C distance: 2.82 ± 0.03 Å). The EXAFS data are analyzed by iterative transformation factor analysis to further verify the chemical speciation, which is calculated on the basis of thermodynamic constants, and the used structural model. The experimental results are in very good agreement with the thermodynamic modelling.     

Infrared absorption by pairs of group III and V impurities in silicon

Infrared absorption bands, shifted to regions of lower energies relative to narrow lines of transitions of impurities to excited states, are investigated in silicon doped with group III and V impurities in concentrations above 10¹⁶ cm^?3. It is found that the band structure is peculiar to each of the investigated impurities but independent of their concentrations, and the absorption coefficients in the bands increase approximately quadratically with concentration. This leads one to infer that the bands are caused by the excitation of charge carriers bound on impurity pairs localized within several Bohr radii.     

Heat capacity of a five-coordinated iron(III) complex,iodobis (N,N-Dimethyldithiocarbamato) iron(III), between 0.4 and 300 K

The heat capacity of iodobis (N, N-dimethyldithiocarbamato)iron(III) has been measured between 0.4 and 300 K. Based on the heat capacity and entropy at low temperatures it was found that the present sample consists of a mixture of monomer (ca. 40%) and dinier (ca. 60%); the former brings about a λ-type phase transition from an antiferromagnetic to a paramagnetic state at T_N = (1.65 ±0.04) K while the latter exhibits a Schottky-ype anomaly due to antiferromagnetic dimeric coupling, the effect of which becomes dominant below ca. 0.7 K. The zero-field splitting parameter of a single ferric ion was estimated to be $\text{D}\text{k}\text{=}\text{D}{}_{\mathrm{D}}\text{k}\text{= 14 K}$ for the monometer and the dimer, while the dimeric coupling constant was $\text{J}{}_{\mathrm{D}}\text{k}\text{= ?0.15 K}$. The entropy at low temperatures cannot be accounted for solely by the spin manifold. Additional contribution from a tunnel-splitting of the rotational levels of four constituent methyl-groups has been discussed. In this case, the level splitting of the ground state is 2.5 J mol^?1 and the barrier height of hindering potential is 2.3 kJ mol^?1.     

Reduction of iron(III) in annealed asbestos/chrysotile

Magnetic and structural properties of Bi substituted YIG with nominal formula of Bi _x Y_3???x Fe₅O₁₂ (x?=?0.0, 0.25, 0.5, 0.75, 1.00) prepared via Mechanochemical Processing (MCP) have been studied with Mossbauer spectroscopy, X-ray diffraction (XRD). The temperature dependence of sublattice magnetic hyperfine field for samples is analyzed. The a–d intersublattice superexchange found to be antiferromagnetic and increases from ??21.97 to ??25.79 k_B as Bi increases from 0.0 to 0.25. The a–a and d–d intrasublattice exchanges for sample x?=?0.0 are 13.18 and 10.55 k_B respectively while for sample x?=?0.25 a–a and d–d intrasublattice exchanges are 7.7 and 8.9 k_B respectively. The correlation of lattice constant and superexchange interaction are discussed.