Basic principles,recent trends and future directions of microextraction techniques for the analysis of aqueous environmental samples

Microextraction-based sample preparation techniques have exhibited remarkable importance in analytical chemistry since they were first developed in the 1980s. The application of these techniques involves efficient and, at the same time, environmentally-friendly analytical methodologies. They are also generally faster when compared with classical sample preparation techniques, requiring low solvent and sample volumes, and also allowing for automated or semi-automated procedures. This paper provides an overview of the basic principles of sample preparation techniques and the important applications and developments that have taken place in this area over the past five years. These procedures include solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), bar adsorptive microextraction (BAμE), rotating disk sorptive extraction (RDSE), micro solid-phase extraction (μ-SPE) and liquid-phase microextraction (LPME). The main variations are discussed with a focus on recent applications in the analysis of environmental water samples. Lastly, some of the trends and perspectives associated with these outstanding microextraction sample preparation approaches are highlighted.     

New insights into the conversion of electropherograms to the effective electrophoretic mobility scale

CE–MS is increasingly gaining momentum as an analytical tool in metabolomics, due to its ability to obtain information about the most polar elements in biological samples. This has been helped by improvements of robustness in peak identification by means of mobility-scale representations of the electropherograms (mobilograms). As a necessary step toward facilitating the use of CE–MS for untargeted metabolomics data, the authors previously developed and introduced ROMANCE, a software automating mobilogram generation for large untargeted datasets through a simple and self-contained user interface. Herein, we introduce a new version of ROMANCE including new features such as compatibility with other types of data (targeted MS data and 2D UV-Vis absorption-like electropherograms), and the much needed additional flexibility in the transformation parameters (including field ramping and the use of secondary markers), more measurement conditions (depending on detection and integration modes), and most importantly tackling the issue of quantitative peak conversion. First, we present a review of the current theoretical framework with regard to peak characterization, and we develop new formulas for multiple marker peak area corrections, for anticipating peak position precision, and for assessing peak shape distortion. Then, the new version of the software is presented and validated experimentally. We contrast the multiple marker mobility transformations with previous results, finding increased peak position precision, and finally we showcase an application to actual untargeted metabolomics data.     

Raman reflection,a possible mechanism for enhancement of Raman scattering by an adsorbed molecule

Calculations illustrate a new physical process, Raman reflection, which contributes to Raman scattering by adsorbed molecules. It is induced by the interaction between the vibrating ion-core charges of adsorbed molecules and the electrons of the metal; this interaction causes energy transfer from the electron-hole pair to the oscillating molecule. Since the energy transferred equals the vibrational energy, the photon emitted by subsequent electron-hole recombination is Raman shifted, augmenting the Raman intensity.     

The axisymmetric equivalent of Kolmogorov's equation

A type of turbulence which is next to local isotropy in order of simplicity, but which corresponds more closely to turbulent flows encountered in practice, is locally axisymmetric turbulence. A representation of the second and third order structure function tensors of homogeneous axisymmetric turbulence is given. The dynamic equation relating the second and third order scalar structure functions is derived. When axisymmetry turns into isotropy, this equation is reduced to the well-known isotropic result: Kolmogorov's equation. The corresponding limiting form is also reduced to the well-known isotropic limiting form of Kolmogorov's equation. The new axisymmetric and theoretical results may have important consequences on several current ideas on the fine structure of turbulence, such as ideas developed by analysis based on the isotropic dissipation rate or such as extended self similarity (ESS) and the scaling laws for the n-order structure functions. Received 20 October 2000 and Received in final form 25 May 2001     

《红楼梦》前80回与后40回某些文风差异的统计分析\,(两个独立二项总体等价性检验的一个应用)

本文以数据分析为基础,应用统计学中``两总体等价性检验'的理论和方法,提供了一个强有力的证据:《红楼梦》前80回与后40回在某些重要的情景描写上确实存在非常显著的差异,这一结论的可信概率不低于98\%.     

Persistency of material element deformation in isotropic flows and growth rate of lines and surfaces

We explore the consequence of isotropy on the growth of material lines and surfaces in complex flows. We show that the key parameter is the persistency , defined as the product of a typical stretching rate to its associated coherence time . In particular, we derive the dependence of the net growth rate of both lines and surfaces on . Their growth rates increase strongly with increasing persistencies for small , and then saturate for . Making use of measurements of Girimaji and Pope [1], we estimate the persistency to be of order 1 in isotropic turbulence. We then comment on the evolution of the shape of an initially spherical material blob. While its length increases, one of its tranverse dimension increases slowly and the other one decreases. This quasi-two-dimensional deformation leads a final ribbon-shape. Received 10 November 1999 and Received in final form 14 August 2000     

New approach for understanding the fundamental chemistry of the oxidative sample digestion in spectrochemical analysis

The process known as “wet digestion” is widely used in analytical chemistry as the most common way of dissolving solid samples for elemental spectrochemical analysis. Wet digestion involves the use of oxidizing reagents and acids–mainly HNO₃, H₂O₂, H₂SO₄, HClO₄, and other complementary acid reagents such as HF, HCl, or their mixtures. Wet digestion has become popular and attractive to users in part owing to the application of modern equipment with new technologies such as temperature-controlled heating blocks, microwave systems, and automated digestion systems, among others. Nonetheless, the use of modern, sophisticated instruments does not change the physical and chemical foundations of the classic chemical process. Until now, simplified equations have been used to explain this process. However, fundamental chemical mechanisms and thermodynamic concepts have been commonly left aside. In this work, the acid digestion of samples has been approached based on the chemical reactions, detailing the role and the effect of main reagents and intermediaries. The reactions that can occur during the digestion process have been specified considering the fundamental thermodynamic properties of the reagents used, especially the oxidizing reagents HNO₃ and H₂O₂. This article will be a beneficial resource for students, instructors, and professionals alike.