Micelles for signal enhancement and novel selectivity of dansyl amino acids

Fluorescence intensity of various chemical species is enhanced in the microenvironment provided by micelles. Parameters which affect fluorescence intensities are examined by using dansyl (Dns) amino acids as the probe. The retention behavior of Dns-amino acids in micellar LC is examined by using ion-exchange-induced stationary phases. The type and concentration of micellar agent and modifier ion as well as concentration of acetonitrile in the mobile phase affect the retention and signal intensity of Dns-amino acids. The order of elution of Dns-amino acids obtained with the micellar mobile phase is very different from that observed in conventional reversed-phase LC. Fluorescence intensities of Dns-amino acids are enhanced by the micellar mobile phase.     

Retention indices in micellar electrokinetic chromatography

The use of retention indices in micellar electrokinetic chromatography (MEKC) is evaluated both from a theoretical and a practical point of view. Fundamental equations for the determination of retention indices in MEKC are described, showing that retention indices are independent of the surfactant concentration. Possibilities as well as limitations of different homologous series as reference standards are described. In addition, the practical application of retention indices for identification, investigation of solute-micelle interactions, characterization and classification of pseudo-stationary phases and determination of solute lipophilicity are discussed.     

Retention models for programmed gas chromatography

The models proposed by many authors for the prediction of retention times and temperatures, peak widths, retention indices and separation numbers in programmed temperature and pressure gas chromatography by starting from preliminary measurements of the retention in isothermal and isobaric conditions are reviewed. Several articles showing the correlation between retention data and thermodynamic parameters and the determination of the optimum programming rate are reported. The columns of different polarity used for the experimental measurement and the main equations, mathematical models and calculation procedures are listed. An empirical approach was used in the early models, followed by the application of thermodynamic considerations, iterative calculation procedures and statistical methods, based on increased computing power now available. Multiple column arrangements, simultaneous temperature and pressure programming, applications of two-dimensional and fast chromatography are summarised.     

半导体光催化研究进展与展望

评述了目前半导体光催化在国内外的研究概况 ,并对存在的问题和未来的发展动向进行简要分析 .列举了近 30年来关于光催化研究的部分成果 ,内容涉及光催化剂的制备 (包括新催化剂的开发 ,TiO2 、ZnO、CdS等光催化剂的各种改性或修饰 )、光催化作用机理研究、光催化技术的工程化、光催化技术的各种应用研究和产品开发等等从基础到应用研究的各个方面 .总体上来看 ,半导体光催化基本上是一个没有选择性的化学过程 ,所以再进行大量的不同反应物的光催化活性的评价研究意义已不是很显著 ,认为未来的半导体光催化研究应该集中在机理的深刻认识、光响应范围宽和量子效率高的催化剂制备、半导体光催化技术工程化及新型光催化产品开发方面 .     

High-sensitivity capillary and microchip electrophoresis using electrokinetic supercharging preconcentration. Insight into the stacking mechanism via computer modeling

This review discusses recent progress in the application of one of the most effective in-line preconcentration techniques used in electrophoresis in capillaries and microchips, electrokinetic supercharging (EKS). Conventionally considered as a transient isotachophoresis (tITP) step put into effect after the electrokinetic sample injection (EKI), EKS presumes that the electrolyte filled into the capillary (or microchip channel) comprises a co-ion acting as a leading ion to stack the injected analytes. Subsequently, to create the tITP state, one needs an additional injection of a suitable terminating ion. As a resulting increase in sensitivity strongly depends on the performance of both EKS stages, two theoretical sections are focused on hints for proper arrangement of EKI and tITP elaborated by means of computer simulation. In particular, factors affecting the injected amount of analytes, different modes of introducing the sample, suitable combinations of leading and terminating ions, and optimization of supporting electrolyte compositions are discussed with an objective to increase the enrichment factors. A comprehensive coverage of recent EKS applications in capillary and microchip electrophoresis, including metal ions, pharmaceuticals, peptides, DNA fragments, and proteins, demonstrates attainable sensitivity enhancements up to two orders of magnitude. This should make this method exportable to other analytes and facilitate its more widespread use to applications that require low limits of detection.     

Retention models for ionizable compounds in reversed-phase liquid chromatography: Effect of variation of mobile phase composition and temperature

General models in reversed-phase liquid chromatography that have been extended to relate retention of ionizable compounds to mobile phase composition, pH and/or temperature are reviewed. In particular, the fundamentals and applications of the solvation parameter model, the polarity parameter model and several classical models based on empirical equations are presented and compared. A main parameter in all these models is the degree of ionization of the acid–base compound, which depends on both the pH of the mobile phase and the acid–base constant of the compound. Thus, on one hand, the different procedures for pH measurement in the mobile phase and their influence on the performance of the models are outlined. On the other hand, equations that relate the variation of the pH of the buffer and the pK_a of the compound with the mobile phase composition and/or temperature are reviewed and their applicability to the retention models critically discussed.     

Micellar chromatography of inorganic compounds

Micellar chromatography has been used to separate various compounds and to determine the partition coefficients of the compounds between aqueous bulk solution and a micellar pseudophase. The application of this method to inorganic analyses is less common than its application to organic analyses, albeit the former application gives fundamental aspects of the micellar partition of simple ions and promises developments of novel separation. In this review, we focus our attention on the fundamental aspects of micellar chromatography mostly in inorganic analysis of simple ions.     

《数学评论》概况和文献检索

本文着重介绍《数学评论》及其索引的有关知识，并提供利用《数学评论》查找数学文献的检索途径．     

Nuclear magnetic resonance approaches to the rationalization of chromatographic enantiorecognition processes

NMR spectroscopy represents a valuable tool for obtaining information about structure and dynamics at a molecular level on the diastereoisomeric complexes formed by enantiomeric substrates and chromatographic chiral selectors or modifiers. Some examples collected from the literature show the potentialities of solution NMR spectroscopy in the rationalization of chromatographic enantiorecognition processes and the different NMR approaches needed according to the chiral selector features.