Chemical state analysis of Al by high resolution X-ray spectroscopy

A quantitative method for chemical state analysis of aluminum was proposed by the combination of high resolution X-ray spectroscopy and the nonlinear least square fitting method. Determination of coordination and population analysis were performed with AlV₂O₄ and clay minerals.     

A method for population and bonding analyses in calculations with extended basis sets

Summary A method for population and bonding analyses in the calculations with extended basis sets is proposed. The definition and evaluation method of the atomic orbitals in molecular environments (AOIMs) are described. It is shown that the AOIMs can be divided into two subsets, the strongly occupied minimal compact subset {AOIM}_B and the very weakly occupied “Rydberg” subset {AOIM}_R, according to the orbital population obtained from Mulliken analysis with AOIMs as basis sets. The viewpoint of “molecular orbitals consisting of minimal atomic orbital sets” can be optimally realized in terms of {AOIM}_B. The Mulliken population based on AOIMs is reasonable and fairly stable to changes of basis sets. The Mayer bond orders calculated based on {AOIM}_B are quite stable to the changes of basis sets; therefore they can be used to measure objectively the contribution of individual atomic orbitals to bonding.     

Extended Hückel theory: A new population analysis and its application to forecast chemical bond lengths

Although widely used, the population analysis proposed by Mulliken has been contested by several authors. A new analysis, very easily computed on the orthogonal basis, is here proposed and applied to the EHT wave function.Under its usual presentation, the EHT method is unable to directly evaluate bond lengths through an energy minimum condition. However, it is possible to settle an empirical quadratic relation between the bond lengthR _rs and a quantity calledp _rs, similar to a bond population. Such relations are given for bonds of the CC, CN, CO, CS, CF, CCl, CBr, CH, NO and OH types.The examination of the variation of the bond population under a variation of the bond length has enabled us to prove that this semi-empirical relation was usable in an iterative process: starting from bond lengths taken from any systematic table, it is possible, for a given molecule, to evaluate the bond length consistent with experimental values within an accuracy of 0.03 Å. Some examples, concerning cyclic or acyclic molecules and various kinds of bonds, are given.     

Determination of methyltin compounds in urine of occupationally exposed and general population by in situ ethylation and headspace SPME coupled with GC-FPD

A method for the determination of methyltin compounds in human urine samples was developed using headspace solid-phase microextration (HS-SPME) coupled with gas chromatographic separation and flame photometric detection. Three methyltin compounds, monomethyltin (MMT), dimethyltin (DMT), and trimethyltin (TMT) were in situ ethylated by sodium tetraethylborate (NaBEt₄) for SPME and GC-FPD analysis. Under the optimized condition, the detection limits of MMT, DMT, and TMT were 8.1, 2.5 and 5.6 ng Sn L⁻¹, and the relative standard deviations were 11.0%, 7.3% and 4.0%, respectively. Methyltin compounds in thirteen urine samples from occupationally exposed population and two from general population were analyzed by the proposed method. The concentrations of total methyltin in the tested urine samples of occupationally exposed population ranged from 26.0 to 7892 ng Sn L⁻¹, and the average level is higher than those of the two non-occupationally exposed individuals. The methyltins in urine were adjusted by osmolality in order to enhance the comparability of different urine samples and the feasibility of this correction method was validated.     

Conformational disorder in 4‐(5,5′‐dibromo‐2′‐chloro‐4,4′‐bipyridyl‐2‐yl)benzaldehyde: role of π–π and halogen interactions

The crystal packing of the title compound, C₁₇H₉Br₂ClN₂O, is governed by strong π–π stacking, where molecules are tightly bound within infinite (100) planes; these planes interact mainly through non‐optimal π–π stacking where arene rings are noticeably displaced from perfect overlap, and also through halogen–halogen interactions. The aldehyde group shows conformational disorder, with a significant population difference between the two conformers; this difference is rationalized by the energetic analysis of the crystal packing using the PIXEL method, which also allows a decomposition of intermolecular interaction energy into Coulombic, polarization, dispersion and repulsion contributions. Using such an analysis, it is found that the main reason for this unequal population of the two conformers in the crystal is two hydrogen bonds that are present only for the major conformer.     

Optimal population analysis

An easy method of approximating the electron density of a molecule by expressing it as a sum of squares of atomic orbitals is described. The coefficients are determined by minimizing the error in the electric field. The optimal population analysis is an integration of this optimized density over the orbitals belonging to one atom. The Mulliken population analysis can be interpreted as the integral of a Mulliken density that is a similar expression with fixed coefficients. The two densities are compared in détail using calculations on the water molecule and, more briefly, HF, LiH, BH, and C₂H₄. The error in the densities is identified and examined. The optimal population analysis is strongly recommended as a practical improvement to the Mulliken populations.     

Application of the Pseudo-Inverse Matrix Method in Non-Isothermal Kinetic Analysis

A method is proposed for evaluation of the activation parameters for reactions which occur under non-isothermal conditions. This method can discriminate between possible differential conversion functions. The proposed method, which was coded into a software package available to the scientific community, is designed to solve an overdetermined systems of equations: da_i/dt=k(T_i)f(a_i) where i equations are to be considered (i can be the number of experimental points). Solution of this overdetermined system with a pseudo-inverse matrix method furnishes the activation parameters and the parameters of the conversion function f(a). Some examples of application of this method in non-isothermal kinetic analysis are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

The separation of beryllium from iron,aluminium and titanium by ion exchange,and its application to the analysis of beryl

A now ion exchange method is proposed for the separation of Befrom Al, Fe, Ti, Ca and phosphate, by prefercntially adsorbing it on cation exchange resin AmberliteIR-120, after complexing the other ions with EDTA and H₂0₂ The successful application of the method to the analysis of beryls is demonstrated     

Determination of nanoparticle sizes by X-ray diffraction

Different procedures for analysis of particle sizes by the X-ray diffraction method are compared by the example of nanoparticles of nickel and iron(3+) oxide (Fe₂O₃). A modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions, and the efficiency of the method is shown. The analysis within the frame-work of the Warren-Averbach method makes it possible to restore the distribution function of nanoparticles (crystallites) over true diameters, which satisfactorily correlates with electron microscopy data. The applicability of the Warren-Averbach method to the estimation of crystallite sizes by the analysis of a single diffraction line is substantiated. The range of the applicability of the Scherrer, Williamson-Hall, Warren-Averbach, and modified Warren-Averbach methods to the substructure analysis by the X-ray diffraction is determined as depending on the method of nanostructure formation.     

AB initio calculations of CH3OH vibrational force constants

SCF equilibrium geometry, population analysis and vibrational force constants of the CH₃OH molecule have been determined ab initio using the SCF LCGO method. A fair agreement with experiment is found. The main result is the asymmetry of the methyl group.     

The thermal stability of chalcogenide glasses

Crystallization processes of Ge_xS_1-x (0.322≤x≤0.44) glasses have been studied by thermal analysis and a new simple method of kinetic analysis is proposed. This method allows the definition of an appropriate model characterizing the crystallization process of glass, as well as calculation of reliable kinetic parameters. Results of kinetic analysis allow definition of a thermal stability criterion which has a general applicability for any glass-forming system. ICTA Young Scientist Award presentation     

HPLC combined with ICP-MS for the determination of trace amounts of rare earth impurities in high-purity La2O3 by using 2-ethylhexyl hydrogen-2-ethylhexylphosphonate resin as a stationary phase

A new method for the determination of trace rare earth impurities in high-purity La₂O₃ by HPLC combined with ICP-MS is proposed. The chromatographic retention behavior of La and Ce in HPLC was studied with 2-ethylhexyl-hydrogen-2-ethylhexylphosphonate (P507) resin as the stationary phase and inorganic acid (HNO₃) as the mobile phase. The effects of acidity of the mobile phase, flow rate of eluent and column oven temperature on the separation of La and Ce were investigated in detail. The results of the effect of different ratios of La / Ce showed that a favorable separation of La and Ce could be obtained easily and rapidly with the method presented. Compared with the conventional open column method, the proposed separation system shows a good performance with regard to short separation time, low reagent consumption, and simple operation. The method has been applied to the analysis of real samples of high-purity La₂O₃ with satisfactory results.     

A simple,sensitive, and specific HPLC amperometric screening method for trace levels of sulphonamides in liver,kidney, and muscle tissues

Summary A simple, sensitive and specific method for the analysis of the residues of sulphonamides in liver, kidney, and muscle tissues is described. The method is based on a simple extraction step, separation on a RP-C₂ column and amperometric detection at +1.10 V. Recoveries were calculated with the aid of sulphamerazine as internal standard. The detection limit of the proposed method is 10 ng/g.     

Kinetic Analysis and Modeling of Thermal Decomposition of Ammonia Borane

Ammonia borane (AB; NH₃BH₃) is one of the most promising materials for hydrogen storage applications, mainly due to its high gravimetric hydrogen storage capacity of 19.6 wt%. In this paper, we present an exclusive kinetic analysis of AB thermolysis. Three methods are used for kinetic analysis of the thermal decomposition of AB, namely the Kissinger method, isoconversional model‐free fitting method, and solid‐state kinetics model–based method. Finally, a need to device a new model for thermal kinetics of AB was observed and hence a new kinetic model for AB thermolysis is proposed.     

The application of x-ray diffraction analysis to uranium ceramics: Quantitative analysis of the binary mixture UO2-U3O8

An X-ray diffraction method is proposed for the quantitative analysis of the binary mixture UO₂—U₃O₈. Diffractometer and Debye-Scherrer camera techniques were compared ; the former is preferable whenever sufficient sample is available. The relative standard deviation was found to be 1%.     

Potential energy surfaces for BeH2 and BH2

The diatomics-in-molecules method has been used to obtain potential energy surfaces (PES) for the molecules BeH₂ and BH₂. The method is used in a way proposed by Tully [1]. The present paper contains an analysis of some features of PES in the vicinity of their crossing near linear configurations of the molecules.     

Application of the Combustion Method in a Closed Flask to the Lead Determination in Atmospheric Aerosols

Abstract

The destruction of the filter for metal determination in atmospheric aerosols is an important step in the analysis. Nowadays the decomposition of this kind of sample has not been completely solved, so it is interesting to study new methods for filter sample attack. In the present work the application of the combustion method in a closed flask for mixed cellulose esters filter decomposition for lead determination is proposed. For this purpose optimum operating conditions as stopper flask design, sample size, flask volume, shaking time and volume and concentration of absorbing solution are established, and accuracy and precision of the proposed method using AAS for the measurements is given. The results obtained by the closed flask combustion are compared with those found by wet attack with HNO₃. The method proposed is rapid, has low reagent contamination and no loss of lead by volatilization or by amalgamation occurs. This method shows an accuracy and a precision in good agreement with the standard method.     

Analysis of uranium in dissolver solution of fast reactor carbide fuel reprocessing

Uranium in simulated dissolver solution of FBTR mixed carbide fuel containing fission products is analyzed by modified Davies–Gray method. The uranium is analyzed after the sample is evaporated with 1 M H₂SO₄ and followed all the steps carried out by Davies–Gray method. The proposed method assures analysis of uranium in dissolver solution of FBTR fuel can be titrated directly without prior separation of fission products.     

HPLC combined with ICP-MS for the determination of trace amounts of rare earth impurities in high-purity La2O3 by using 2-ethylhexyl hydrogen-2-ethylhexylphosphonate resin as a stationary phase

A new method for the determination of trace rare earth impurities in high-purity La₂O₃ by HPLC combined with ICP-MS is proposed. The chromatographic retention behavior of La and Ce in HPLC was studied with 2-ethylhexyl-hydrogen-2-ethylhexylphosphonate (P507) resin as the stationary phase and inorganic acid (HNO₃) as the mobile phase. The effects of acidity of the mobile phase, flow rate of eluent and column oven temperature on the separation of La and Ce were investigated in detail. The results of the effect of different ratios of La / Ce showed that a favorable separation of La and Ce could be obtained easily and rapidly with the method presented. Compared with the conventional open column method, the proposed separation system shows a good performance with regard to short separation time, low reagent consumption, and simple operation. The method has been applied to the analysis of real samples of high-purity La₂O₃ with satisfactory results. Received: 8 September 1999 / Revised: 5 January 2000 / Accepted: 7 January 2000