Application of indirect methods in analysis by atomic-absorption spectrometry

The use of indirect methods for the determination by atomic-absorption spectrometry of those elements not normally amenable to sensitive determination by this technique is reviewed. The available indirect methods are classified into five general types of procedure; specific reported procedures for the determination of metals, non-metals and some compounds are discussed.     

Computation of correlation functions and wave function projections in the context of quantum trajectory dynamics

The de Broglie-Bohm formulation of the Schrodinger equation implies conservation of the wave function probability density associated with each quantum trajectory in closed systems. This conservation property greatly simplifies numerical implementations of the quantum trajectory dynamics and increases its accuracy. The reconstruction of a wave function, however, becomes expensive or inaccurate as it requires fitting or interpolation procedures. In this paper we present a method of computing wave packet correlation functions and wave function projections, which typically contain all the desired information about dynamics, without the full knowledge of the wave function by making quadratic expansions of the wave function phase and amplitude near each trajectory similar to expansions used in semiclassical methods. Computation of the quantities of interest in this procedure is linear with respect to the number of trajectories. The introduced approximations are consistent with approximate quantum potential dynamics method. The projection technique is applied to model chemical systems and to the H+H(2) exchange reaction in three dimensions.     

An improvement on the two-dimensional convolution method of image reconstruction and its application to SPECT

In single-photon emission computed tomography (SPECT) and X-ray CT one-dimensional (1-D) convolution method is used for their image reconstruction from projections. The method makes a 1-D convolution filtering on projection data with a 1-D filter in the space domain, and back projects the filtered data for reconstruction. Images can also be reconstructed by first forming the 2-D backprojection images from projections and then convoluting them with a 2-D space-domain filter. This is the reconstruction by the 2-D convolution method, and it has the opposite reconstruction process to the 1-D convolution method. Since the 2-D convolution method is inferior to the 1-D convolution method in speed in reconstruction, it has no practical use. In the actual reconstruction by the 2-D convolution method, convolution is made on a finite plane which is called convolution window. A convolution window of size N X N needs a 2-D discrete filter of the same size. If better reconstructions are achieved with small convolution windows, the reconstruction time for the 2-D convolution method can be reduced. For this purpose, 2-D filters of a simple function form are proposed which can give good reconstructions with small convolution windows. They are here defined on a finite plane, depending on the window size used, although a filter function is usually defined on the infinite plane. They are however set so that they better approximate the property of a 2-D filter function defined on the infinite plane. Filters of size N X N are thus determined. Their value varies with window size. The filters are applied to image reconstructions of SPECT.(ABSTRACT TRUNCATED AT 250 WORDS)     

BaTiO3的电子结构和光学性质

采用第一性原理赝势平面波方法, 在局域密度近似(LDA)和广义梯度近似(GGA)下分别计算了BaTiO3立方相和四方相的电子结构, 并在局域密度近似下计算了BaTiO3立方相的光学性质. 结果表明, BaTiO3立方相和四方相都为间接带隙, 方向分别为Γ-M和Γ-X, 大小分别为2.02和2.20 eV. 对BaTiO3和PbTiO3铁电相短键上电子布居数的对比分析, 给出了它们铁电性大小的差别. 且在30 eV的能量范围内研究了BaTiO3 的介电函数、吸收系数、折射系数、湮灭系数、反射系数和能量损失系数等光学性质,并基于电子能带结构对光学性质进行了解释. 计算结果与实验数据相符合.     

Structural and optical properties of a neutral Nickel bisdithiolene complex: density functional versus ab initio methods

Density functional theory (DFT) and ab initio computations are applied to examine different properties of diamagnetic, square planar neutral nickel complexes that contain two bidentate ligands derived from bis ((ethylene)-1,2-dithiolato) ligands. Geometry, vibrational spectra (IR and Raman) are well reproduced in the density functional framework whereas TD-DFT methods are clearly insufficient to reproduce absorption properties. Multiconfigurational perturbation theory based on a complete active space self-consistent field wave function, i.e. MRPT2 and MRPT4 methods, reveal the pronounced multiconfigurational character of the ground state wave function. The singlet–triplet energy gap, the energy gained from symmetry breaking and the singlet diradical character are discussed in the DFT and ab initio frameworks. The complex of interest does not display a strong singlet diradical character. This molecule having a peculiar electronic structure; strong delocalization as shown by a new electron pair localization function analysis (EPLF); exemplifies the fragility of the TD-DFT method and thus, caution should be taken in the determination of the energetic properties of such compounds.     

Application of polyethylene glycol for "electrochemical masking" in direct-current polarography

The use of polyethylene glycols (PEG) of molecular weight from 200 to 15,000 for electrochemical masking has been investigated. A pH-4.4 tartrate buffer was found to be the most suitable supporting electrolyte, and 0.1% the optimum PEG concentration. PEGs of m.w. below 600 had little effect on the waves examined, and are useless for electrochemical masking. Under the conditions chosen, the waves of Bi(III), Sb(III) and In(III) are completely suppressed; the Cd(II) and Pb(II) waves are shifted to more negative potentials, and the Tl(I) wave is scarcely affected by PEGs. The Cu(II) wave behaves differently from the others. A method is proposed for the determination of lead and/or thallium in the presence of up to 5000-fold w/w ratios of bismuth, antimony or indium. The determination of both lead and thallium is only possible when the amounts are not too different, as the waves are quite close. Copper(II) interferes.     

Determination of soliton width and density by NMR-NQR

NQR-Spectra of incommensurately modulated structures show typical frequency distributions owing to the fact, that the displacements from the parent commensurate structure are in general different for each atom. The modulation can change gradually from a plane wave to a multisoliton lattice with the temperature. Comparing the measured shape of the spectrum with the one calculated from the form of the modulation wave allows a determination of the density of solitons. This is demonstrated on the example of Rb₂ZnCl₄.     

氢醌对胆红素氧化过程的促进作用及其分析意义

研究了氢醌与胆红素的作用过程，发现氢醌在碱性条件下可促使胆红素氧化，且胆红素被氧化成胆绿素，此反应过程被证实为自由基反应，考察了介质条件，抗氧化剂等反应过程的影响及其它酚类物质对胆红素氧化的作用情况。     

高效毛细管电泳在糖分析中的应用

本文评述了近年来毛细管电泳在糖分析中的发展状况和一些常见的分析方法，引用文献５１篇。     

Absolute determination of the conductivity of electrolytes. Double differential cell with adjustable constant

Existing methods for the determination of the electrical conductivity of electrolytes require a cell calibration by an indirect method and the determination of their electrical resistance. A new conductivity cell is described which is a double differential cell with an adjustable constant. Using this cell, absolute determination of the conductivity of electrolytic solutions can be obtained over a wide temperature range. The influence of the frequency is either eliminated or greatly reduced in all other cases. The accuracy is at least as good as that obtained by indirect methods.This paper is part of a Ph.D. dissertation by the author.     

Benchmarking NMR indirect nuclear spin-spin coupling constants: SOPPA, SOPPA(CC2), and SOPPA(CCSD) versus CCSD

Accurate calculations of NMR indirect nuclear spin-spin coupling constants require especially optimized basis sets and correlated wave function methods such as CCSD or SOPPA(CCSD). Both methods scale as N(6), where N is the number of orbitals, which prevents routine applications to molecules with more than 10-15 nonhydrogen atoms. We have therefore developed a modification of the SOPPA(CCSD) method in which the CCSD singles and doubles amplitudes are replaced by CC2 singles and doubles amplitudes. This new method, called SOPPA(CC2), scales only as N(5), like the original SOPPA-method. The performance of the SOPPA(CC2) method for the calculation of indirect nuclear spin-spin coupling constants is compared to SOPPA and SOPPA(CCSD) employing a set of benchmark molecules. We also investigate the basis set dependence by employing three different basis sets optimized for spin-spin coupling constants, namely the HuzIV-su4, ccJ-pVTZ, and ccJ-pVQZ basis sets. The results of the corresponding CCSD calculations are used as a theoretical reference.     

A combined electronegativity equalization and electrostatic potential fit method for the determination of atomic point charges

We report an approach for the determination of atomic monopoles of macromolecular systems using connectivity and geometry parameters alone. The method is appropriate also for the calculation of charge distributions based on the quantum mechanically determined wave function and does not suffer from the mathematical instability of other electrostatic potential fit methods.     

Rapid determination of the critical micelle concentration by Taylor dispersion analysis in capillaries using both direct and indirect detection

The critical micelle concentration is a basic characteristic of surfactants. In this article, the process of formation of micelles is studied by Taylor dispersion analysis using capillary electrophoresis instrumentation as a substituent of capillary liquid chromatography. New methods for determination of critical micelle concentration are presented. Sodium octylbenzene sulfonate and sodium dodecylsulfate are used as model compounds with and without chromophore. Two novel approaches based on indirect ultraviolet detection and indirect Taylor dispersion analysis with direct ultraviolet detection are introduced for the determination of critical micelle concentration value of surfactant without any chromophore. The determined critical micelle concentration values are in correspondence with the tabulated values at 95% confidence level.     

Determination of mebendazole

Direct and indirect non-aqueous titrimetric methods for the determination of mebendazole are presented. These methods are reproducible, with relative standard deviations of 0.3%. Mebendazole in tablets (100 mg per tablet) has also been determined spectrophotometrically with use of perchloric acid as solvent. The relative standard deviation was 1.4%. The methods are easy to automate for routine analysis.     

Determination of dye/protein ratios in a labeling reaction between a cyanine dye and bovine serum albumin by micellar electrokinetic chromatography using a diode laser-induced fluorescence detection

The degree of labeling, i.e., dye/protein ratio (D/P) is important for characterizing properties of dye labeling with proteins. A method for the determination of this ratio between a fluorescent cyanine dye and bovine serum albumin (BSA), based on the separation of the labeling mixture using micellar electrokinetic chromatography with diode laser-induced fluorescence detection, is described. Two methods for the determination of D/P were examined in this study. In these methods, a hydrolysis product and impurities, which are usually unfavorable compounds that are best excluded for protein analysis, were utilized to determine the amounts of dye bound to BSA. One is a direct method in which a ratio of the peak area of BSA to the total peak area of all the products produced in the labeling reaction was used for determining the average number of dye molecules bound to a single BSA molecule. The other is an indirect determination, which is based on diminution of all peak areas related to the products except for the labeled BSA. These methods were directly compared by means of a spectrophotometric method. The experimental results show that the indirect method is both reliable and sensitive. Therefore, D/P values can be determined at trace levels using the indirect method.     

Dosage polarographique indirect de l'ton potassium

An indirect polarographic method for the determination of potassium has been established. It is based on the difference in height of the wave due to dipicrylamine before and after addition of the potassium which has to be determined. 0.5–2 mg potassium can be determined with an average accuracy of 3 %.     

The distribution of electronic charge in the ground state of cubic boron nitride

The distribution of electronic charge in cubic boron nitride is investigated using the bond orbital wave functions recently calculated by Coulson and Doggett. Plots of the one-electron density function, in the (110) plane, are found to be insensitive to the choice of atomic basis functions, in contradistinction to the previously calculated effective atomic charges. A number of structure amplitudes are also calculated for each of the bond orbital wave functions.     

Simultaneous determination of nuclear and electronic wave functions without Born–Oppenheimer approximation: Ab initio NO+MO/HF theory

We develop a simultaneous determination method of nuclear and electronic wave functions without the Born–Oppenheimer approximation. We examine two expanding methods, namely, molecular orbital (MO)-type and valence bond (VB)-type expansions for a nuclear orbital, which is a one-particle wave function of a nucleus. The VB-type expansion is shown to be more accurate than the MO-type one because of the local nature of the nuclei. We also investigate the basis function expansion of the nuclear orbital and propose a scheme to determine the orbital exponent for the nuclear basis function. Numerical calculations confirm the accuracy and feasibility of the present method. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001