Simultaneous Spectrophotometric Determination of Group B Vitamins Using Parallel Factor Analysis: PARAFAC

In this work, a simple and rapid analytical procedure was applied for simultaneous determination of folic acid (vitamin B₀), thiamin (vitamin B₁), riboflavin (vitamin B₂) and pyridoxal (vitamin B₆) based on the absorbance data in the pH range 2.0‐12.0 at 25 °C using parallel factor analysis (PARAFAC). The effect of the pH as the most important factor on the sensitivity of the determination was studied. The spectral data were recorded in 400‐650 nm intervals and a 2‐12 pH range for all four vitamins. The calibration set was constructed in the concentration ranges of 4‐22, 1‐20, 6‐26, and 4‐20 μg mL^?;1 for B₆,B₂,B₁ and B₀, respectively. The root mean squares errors of prediction for the prediction set, (RMSEP), are 0.65, 0.63, 1.13 and 0.34 for B₀,B₁,B₂ and B₆, respectively. The recovery percent for the validation set are in the range of 90.6 to 107.0%. The effect of the experimental conditions and diverse species were discussed. The optimum values of these factors were searched according to the relative standard deviation of the prediction set of mixtures solutions.     

Second derivative spectrophotometric method for simultaneous determination of cobalt, nickel and iron using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

A simple, sensitive and rapid derivative spectrophotometric method using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been developed for simultaneous determination of Co(II), Ni(II) and Fe(II) which have very similar chemical behavior and appear together in many real samples. The complexes of all these metal ions with 5-Br-PADAP were formed immediately at pH 7.0 ammonium acetate buffered solution and were stable for at least 24 h. Second derivative spectra were selected for evaluation, because working wavelength determination was more precise and spectral overlap was less than in the ordinary and first derivative spectra. Three wavelengths at which the complexes exhibit extremum ²D values for Co(II), Ni(II) and Fe(II) were selected as analytical wavelengths, i.e., 640, 600 and 740 nm, respectively. Calibration curves drawn with zero-to-peak values at mentioned wavelengths were linear between 80 and 2000 ng ml⁻¹ for each metal ion. Concentrations of Co(II) and Ni(II) were calculated from the total ²D values and the sum of the linear equations for these three cations at 640 and 600 nm, after Fe(II) assay by making use of the ²D value at 740 nm. Limits of detection (LOD) for Co(II), Ni(II) and Fe(II) were 2.7, 13.9 and 3.0 ng ml⁻¹, respectively. The method has been applied to tool steel and heater resistance wire samples successfully.     

Progress on phthalocyanine-conjugated Ag and Au nanoparticles: Synthesis,characterization, and photo-physicochemical properties

Phthalocyanine (Pc) complexes are an important class of dyes with numerous (e.g., biological, photophysical, and analytical) applications. Among the methods used to improve the properties of these complexes, one should mention the introduction of different substituents, variation of the central metal ion, ligand exchange, and conjugation to nanomaterials (e.g., carbon-based nanomaterials and metal nanoparticles (NPs)). This work briefly reviews Pc complex conjugation to Ag and Au NPs, highlights the different NP shapes, and discusses the diversity of conjugation approaches. Moreover, the use of UV–Vis spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy, dynamic light scattering and Fourier transform infrared spectroscopy to characterize Pc-NP hybrids is summarized. The effect of conjugation on Pc photo-physicochemical properties (fluorescence, singlet oxygen generation, triplet state formation, and optical limiting behavior) is discussed, and future perspectives for the synthesis and applications of new hybrids are provided.     

Characterization of thermo-oxidative stability of polymer optical fibers using chemiluminescence technique

The thermo-oxidative stability of commercially available polymer optical fibers (POFs) and their components (cores and claddings) was investigated. All the bare POFs (core and cladding only) studied here were based on poly(methyl methacrylate) (PMMA) core. The fibers were exposed to 100 °C/low humidity for about 4200 h. Chemiluminescence (CL) technique was applied to investigate the thermo-oxidative stability and for measuring the transmission loss during exposure a prototype device called multiplexer was used. POFs exhibited variation in thermo-oxidative stability although they possessed identical core material PMMA. This was due to difference in the chemical compositions of claddings. Claddings were more susceptible to the thermo-oxidative degradation compared to cores. The thermo-oxidative degradation of both the cladding and the core was found in POFs as a result of climatic exposure. POFs showed an early drop-off followed by a slow decline of transmission. The early drop-off of transmission was attributed to physical changes like thermal expansion and the slow decline of transmission to chemical changes like oxidative degradation of POFs. A good linear relationship between optical transmission stability and thermo-oxidative stability of POFs was established from these studies.     

An electrothermal vaporization unit with axially focusing convection upstream. Part II: Modeling of the condensation process

A model is presented that describes quantitatively the condensation of analytes in pico- and nanogram masses sampled with electrothermal vaporization (ETV). It presumes that the analyte vapor condensation of such low amounts occurs mainly heterogeneously, predominantly on growing carbon particulates originating from the graphite furnace before the analyte vapor achieves saturation via cooling. The model regards the coagulation of carbon particles and the diffusion of analyte atoms. The criterion whether or not an analyte atom sticks to a colliding particle is chosen as a function depending on its temperature and on the common GFAAS pretreatment temperatures. Heterogeneous condensation of six analytes with different volatilities, Ag, Cu, Fe, Ni, Mn, and Pb, is calculated for the ETV unit with an axially focusing convection upstream described in Part I. Modifier effects are taken into account. The results are compared to measured data.     

量化方法研究分子结BEMP和TEMP的电子输运特性

通过结合杂化密度泛函和前线轨道理论与弹性散射格林函数方法研究了BE- MP(benzene-1,4-di-ethynyl-4-mercaptophenyl)和TEMP(thiophene-2,5-di-ethynyl-4- mercaptophenyl)两分子结的输运性质。基于杂化密度泛函方法计算两扩展分子电子结构的基础上,计算了两分子的输运性质．计算结果显示:电流增加来源于电极和分子轨道的共振;电导曲线呈现出平台特征．在此基础上从扩展分子A(Au-BEMP-Au)中间的苯环的旋转而引起电流减小的角度解释了负微分电阻现象．     

用新型AP树脂分离铑—铱和同时富集测定铑`铱`铂`钯

铑-铱分离-向被认为是最困难的课题之一,即使文献曾报道Rh-Ir的分离,但实际Rh并未与萃取剂或吸附剂反应,而是与非贵金属离子一同留在溶液中。我们曾用光谱半定量方法研究了AP树脂对Rh、Ir的吸附行为,结果是Rh不被吸附而Ir能被吸附。本文通过改变Rh的离子状态,使之能被AP树脂吸附完全,而与留在溶液中的非贵金属分离,然后在柱上用不同淋洗液再使Rh-Ir分离。     

Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

Field-induced structural ordering in electrorheological fluids

Structural relaxations of an electrorheological fluid (ERF) due to changes in the applied electrical field strength or shear rate are observed on time scales 1 s<t<40 000 s. Commercial ERFs consisting of mesoscopic polyurethane particles in a silicone oil matrix were studied by three different experimental techniques in order to obtain and compare the characteristic relaxation times. It is demonstrated that dielectric spectroscopy, viscosimetry and light transmission experiments represent the same results concerning the structural relaxation phenomena of ERFs when electrical fields are applied. The tendency of strong induced dipoles to align the particles in the direction of the field increases the effective dipole moment and therefore , the shear viscosity and the amount of light transmitted along the field direction in an ITO/glass sandwich cell. The optical experiment is capable of resolving fast processes within the first 1 ms if large electrical fields are applied. The effects of electrophoresis and shearing, which both counteract the field induced structures, are also addressed.