Bestimmung von stickstoff in refraktärmetallen—I molybdän und wolfram

This is a report on round-robin tests concerning the determination of nitrogen traces in molybdenum and tungsten, which were carried out by the refractory metals group of the chemistry section of the Gesellschaft Deutscher Metallhütten- und Bergleute. The following methods were used: classical and modified Kieldahl methods (in particular, a newly developed micro-Kjeldahl method), inert-gas fusion, vacuum fusion and ultrahigh-vacuum diffusion extraction. As the nitrogen values obtained by the first round-robin test exhibited considerable scatter, possible shortcomings of the various Kjeldahl methods, as well as the quantitative nitrogen recovery by the extraction methods, were carefully examined. The second round-robin test then gave the following results: the nitrogen content of the investigated molybdenum sheet was 2 ppm, the content of the tungsten sheet 0.5 ppm. Classical Kjeldahl methods are not applicable to the determination of nitrogen contents below 10 ppm. Frequently, detection limits of Kjeldahl methods range considerably above 10 ppm, mainly because of contamination by reagents and/or the laboratory atmosphere. The micro-Kjeldahl method and the hot-extraction and fusion-extraction methods are capable of determining nitrogen contents down to 1 ppm at best. The only method available for nitrogen determinations in metals at sub-ppm levels is by ultrahigh-vacuum diffusion extraction. The good agreement between the nitrogen values obtained for molybdenum by the micro-Kjeldahl method and by the various extraction methods is the most reliable proof of the quantitative nitrogen recovery by the extraction methods.     

Flow “Fine” Synthesis: High Yielding and Selective Organic Synthesis by Flow Methods

The concept of flow “fine” synthesis, that is, high yielding and selective organic synthesis by flow methods, is described. Some examples of flow “fine” synthesis of natural products and APIs are discussed. Flow methods have several advantages over batch methods in terms of environmental compatibility, efficiency, and safety. However, synthesis by flow methods is more difficult than synthesis by batch methods. Indeed, it has been considered that synthesis by flow methods can be applicable for the production of simple gasses but that it is difficult to apply to the synthesis of complex molecules such as natural products and APIs. Therefore, organic synthesis of such complex molecules has been conducted by batch methods. On the other hand, syntheses and reactions that attain high yields and high selectivities by flow methods are increasingly reported. Flow methods are leading candidates for the next generation of manufacturing methods that can mitigate environmental concerns toward sustainable society.     

Supramolecular interaction of transition metal complexes with albumins and DNA: Spectroscopic methods of estimation of binding parameters

Binding parameters of metal complexes with albumins and DNA since the middle of 1990s are considered and summarized. The most widespread spectroscopic methods of estimation of binding parameters are discussed – direct fluorescent methods, indirect fluorescent methods (by fluorescence quenching parameters), and ways of estimation of binding constants by other optical spectroscopic methods. The methods and approaches to calculations used for the determination of binding constants are discussed. The data on the already found binding constants and kinetic parameters is systematized.     

Rapid ultraviolet spectrophotometric and liquid chromatographic methods for the determination of natamycin in lactoserum matrix

Two rapid and simple methods were developed for the determination of natamycin in lactoserum matrix by ultraviolet (UV) spectrophotometry and liquid chromatography (LC) with diode-array detection. The methods involve protein precipitation with methanol, followed by centrifugation. No cleanup is necessary. The applicable concentrations of natamycin in lactoserum range from 2 to 500 mg/L for samples analyzed by both methods. The detection and quantitation limits are 0.07 and 0.23 mg/L, respectively, for the UV spectrophotometric method and 0.1 and 0.32 mg/L, respectively, for the LC method. The methods were applied satisfactorily to the determination of natamycin in various commercial lactosera. Both methods were validated independently by standard additions and Youden methodologies, which verified their accuracy. Once the 2 proposed methods were validated independently, the validation of one method was carried out with the other.     

Linear-scaling computation of excited states in time-domain

The applicability of quantum mechanical methods is severely limited by their poor scaling.To circumvent the problem,linearscaling methods for quantum mechanical calculations had been developed.The physical basis of linear-scaling methods is the locality in quantum mechanics where the properties or observables of a system are weakly influenced by factors spatially far apart.Besides the substantial efforts spent on devising linear-scaling methods for ground state,there is also a growing interest in the development of linear-scaling methods for excited states.This review gives an overview of linear-scaling approaches for excited states solved in real time-domain.     

Improved variable reduction in partial least squares modelling based on predictive-property-ranked variables and adaptation of partial least squares complexity

The calibration performance of partial least squares for one response variable (PLS1) can be improved by elimination of uninformative variables. Many methods are based on so-called predictive variable properties, which are functions of various PLS-model parameters, and which may change during the variable reduction process. In these methods variable reduction is made on the variables ranked in descending order for a given variable property. The methods start with full spectrum modelling. Iteratively, until a specified number of remaining variables is reached, the variable with the smallest property value is eliminated; a new PLS model is calculated, followed by a renewed ranking of the variables. The Stepwise Variable Reduction methods using Predictive-Property-Ranked Variables are denoted as SVR-PPRV. In the existing SVR-PPRV methods the PLS model complexity is kept constant during the variable reduction process. In this study, three new SVR-PPRV methods are proposed, in which a possibility for decreasing the PLS model complexity during the variable reduction process is build in. Therefore we denote our methods as PPRVR-CAM methods (Predictive-Property-Ranked Variable Reduction with Complexity Adapted Models). The selective and predictive abilities of the new methods are investigated and tested, using the absolute PLS regression coefficients as predictive property. They were compared with two modifications of existing SVR-PPRV methods (with constant PLS model complexity) and with two reference methods: uninformative variable elimination followed by either a genetic algorithm for PLS (UVE-GA-PLS) or an interval PLS (UVE-iPLS). The performance of the methods is investigated in conjunction with two data sets from near-infrared sources (NIR) and one simulated set. The selective and predictive performances of the variable reduction methods are compared statistically using the Wilcoxon signed rank test. The three newly developed PPRVR-CAM methods were able to retain significantly smaller numbers of informative variables than the existing SVR-PPRV, UVE-GA-PLS and UVE-iPLS methods without loss of prediction ability. Contrary to UVE-GA-PLS and UVE-iPLS, there is no variability in the number of retained variables in each PPRV(R) method. Renewed variable ranking, after deletion of a variable, followed by remodelling, combined with the possibility to decrease the PLS model complexity, is beneficial. A preferred PPRVR-CAM method is proposed.     

Preconcentration techniques for trace analysis via neutron activation

A review is given of the methods that have been proposed for enrichment of trace elements in samples that are to be analysed by neutron-activation methods. The emphasis is on classification of methods, with full illustrations by means of practical examples.     

橡胶贮存寿命预测方法研究进展与思考建议

概述了用数学模型法预测橡胶贮存寿命的方法,包括阿伦尼斯模型,用ASTM D412评估橡胶拉伸性能,应力应变老化模型,压缩永久变形的预测方法,橡胶疲劳寿命损伤模型,用有限元法考核橡胶的裂纹长度与抗裂能之间的关系,基于叠加原理的寿命预测模型等,针对上述模型预测研究结果提出了相关思考建议。认为以老化动力学为基础预测材料寿命的数学模型法发展非常迅速,建议深入研究并拓宽应用;在透彻了解和掌握必需的分子结构参数的基础上,如果结合计算机技术模拟长期贮存或使用条件,对橡胶老化反应机理的研究可能是一个有前景的发展方向。     

三维人脸识别算法研究

近年来,基于三维图像的人脸识别技术已经取得了很大进展,在约束环境下也能获得很好的识别性能,但仍受限于姿态、表情等因素,需要从算法上改进才能解决其影响。本文分别从基于空域直接匹配、基于局部特征匹配和基于整体特征匹配3个角度出发,对人脸匹配算法以及融合算法进行了研究,列出了部分改进算法的实验结果,并分析了算法有效性的原因,总结了目前面临的三维人脸识别算法难以突破的一些困难及未来的研究趋势。     

Interlaboratory experiment srok-1

The concentration and isotopic composition of uranium were determined in a solution of burnt WWER reactor fuel. The isotopic composition was determined by mass spectrometry, whereas for determining the concentration of uranium various methods were used. The interlaboratory mean square errors of the determination of uranium concentration by isotopic dilution analysis and by chemical methods were 0.37 and 1 rel.%, respectively, the content being 2.06 mg U/g fuel solution. The mean uranium concentrations obrained by both methods differ from each other by 1.04 rel.%.     

Spectroelectrochemical processes in polyaniline films prepared by different methods

Basic in situ spectroelectrochemical methods of the studying of the polyaniline electrosynthesis processes and doping-dedoping of the polyaniline films prepared by different procedures are overviewed. The advantages of the combining of different spectroelectrochemical methods in a single experiment are discussed and the extra information on the processes of electrosynthesis and electrochemical doping-dedoping of polyaniline prepared by the combinations of methods is analyzed. Components of the polyaniline electronic absorption spectra are analyzed and spectroelectrochemical properties of polyaniline films prepared by vacuum evaporation are studied by a complex of methods; the results of the studies are presented.     

Equivalence volumes in potentiometric titrations

The development of methods for finding the equivalence volume by using linear regression methods is reviewed. The methods discussed are mainly those developed and used at the Department of Analytical Chemistry at the Royal Institute of Technology in Stockholm. No attempt has been made to cover the large number of methods of finding the equivalence volume in potentiometric titrations developed elsewhere.     

树舌及其提取物中锌锰铜铁含量分析

采用火焰原子吸收分光光度法测定了树舌及其不同提取物中Ｚｎ,Ｍｎ,Ｃｕ,Ｆｅ含量,考虑了提取方法对中药微量元素含量的影响。结果证明,不同提取方法对中药微量元素含量有明显影响。在制剂生产中,应选择适宜的提取炮制方法的生产工艺。     

Colorimetric and Atomic Absorption Spectrometric Determination of Some Heterocyclic Nitrogenous Compounds of Pharmaceutical Interest

Abstract

Simple spectroanalytical methods are proposed for the determination of five heterocyclic nitrogenous compounds. The suggested methods depend upon the formation of the ion-pair complexes of the studied compounds with ammonium reineckate followed by colorimetric and atomic absorption measurement of the complexes solutions. The proposed methods were applied to the determination of some pharmaceutical dosage forms containing the studied compounds. Results obtained were in agreement with those obtained by official and compendium methods.     

Critical parameters of chlorinated tetramethyl- and tetraethylgermane

The critical parameters of chlorinated tetramethyl- and tetraethylgermane were determined by calculational methods. The reliability of calculated data was confirmed by several independent methods.     

The determination of fluoride in environmentally relevant matrices

This report covers analytical methods for the determination of total fluoride in gaseous emissions, rain water and aqueous effluents, vegetation, human urine, factory air and environmental air. All the methods are based on final measurement of fluoride by means of the fluoride ion-selective electrode. Interferences which cannot be eliminated by the masking power of the TISAB buffer solution are avoided by separation of fluoride by steam distillation. Decomposition methods are used for vegetation and for samples which may contain insolubles such as stack gases or aqueous effluents. Sampling of fluoride from air is done by alkaline absorption for the high concentration range (stack gases) and by filter methods for low fluoride concentrations, e.g., in factory and environmental air. Detection limits as low as 0.3 μg m^?3 fluoride can thus be achieved. The methods were established after the individual analytical procedures, common in the various member countries of CTEF, had been compared. Thus, the most practicable method was selected or an optimized version was designed for full testing. The accuracy of the different methods was verified by comparative tests.     

Certification of standard reference materials containing bitter orange

A suite of three dietary supplement standard reference materials (SRMs) containing bitter orange has been developed, and the levels of five alkaloids and caffeine have been measured by multiple analytical methods. Synephrine, octopamine, tyramine, N-methyltyramine, hordenine, total alkaloids, and caffeine were determined by as many as six analytical methods, with measurements performed at the National Institute of Standards and Technology and at two collaborating laboratories. The methods offer substantial independence, with two types of extractions, two separation methods, and four detection methods. Excellent agreement was obtained among the measurements, with data reproducibility for most methods and analytes better than 5% relative standard deviation. The bitter-orange-containing dietary supplement SRMs are intended primarily for use as measurement controls and for use in the development and validation of analytical methods. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of kinetic mechanisms for reactions measured with thermoanalytical instruments

The work considers the methods and techniques, allowing the assignment of the kinetic mechanisms to the chemical reactions evaluated from signals of thermoanalytical measurements. It describes which information about the kinetic mechanisms can be found from either model-free or model-based methods. The work considers the applicability of both methods and compares their results. The multiple-step reactions with well-separated peaks can be equally analyzed by both methods, but for overlapping peaks or for simultaneously running parallel reactions the model-free methods provide irrelevant results.     

动力学过程的精确模拟

采用加权最小二乘法更精确地模拟了化学动力学过程,结出了几种常见动力学模型的权重函数。用普通最小二乘法和加权最小二乘法对聚时苯二甲酸乙二酯的结晶动力学过程进行了处理。方差分析表明,两种加权最小二乘法的标准差均小于普通最小二乘法的标准差,所得斜率和截距也有明显不同,示出了模拟的相对结晶度及其导数曲线。     

Focused microwave-assisted Soxhlet extraction of acorn oil for determination of the fatty acid profile by GC–MS. Comparison with conventional and standard methods

A study of the feasibility of focused microwave-assisted Soxhlet extraction of acorn oil and comparison of results from analysis of trans fatty acids in the oil thus obtained with those for oils obtained by use of other methods commonly used for oil extraction are reported here. The proposed method was optimized by means of a 21-experiment screening design to determine, by means of a reduced number of experiments, which factors affect both extraction efficiency and the degree of unsaturation of the fatty acids in the oil. The proposed method enables total extraction of the fatty acids in 30 min, which is much less than the time required by the Folch (4.5 h), Soxhlet (16 h), and ISO (8 h) reference methods and the stirring–extraction method (56 h). The efficiency of extraction achieved by use of the proposed method is statistically equivalent to that achieved by use of the other methods; the composition of the extracts obtained by use of the proposed method and the Folch and stirring reference methods are also statistically similar. No trans fatty acids were present in the extracts obtained by use of the Folch, stirring, and proposed methods but they were detected in the extracts obtained by use of both the Soxhlet and ISO methods.