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    Dean J.R. (1998) Extraction Methods for Environmental Analysis.

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    Раздел: Химия >>Методы
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    Pollution of the environment poses a threat to the health and wealth of every nation. Consequently it is essential to monitor the levels of organic pollutants in the environment. This book strives to highlight the traditional approaches of sample preparation for organic samples that have been, and continue to be, used whilst also considering modern alternatives. The reader is encouraged not only to use the book as a guide to the different approaches that are currently available, but also to consider what alternatives there may be just around the corner.

    The book is broadly divided in to two areas: aqueous samples and solid samples. In the case of aqueous samples the methods are based on approaches for preconcentrating the analytes from a large volume of water. In contrast, solid samples involves methods for the extraction of analytes from solid or semisolid samples. As the book is mainly concerned with the procedures for preconcentration/extraction, only a brief overview of chromatographic methods of analysis (Chapter 1) is provided. In addition, Chapter 1 covers introductory aspects for the sampling of aqueous and solid matrices, storage and preservation of samples, and quality assurance in environmental analysis. Each area (aqueous or solid samples) is introduced to provide the essentials as to why it is necessary to monitor aqueous or solid samples. Aqueous samples are introduced by the use of a case study concerned with pesticides in the aquatic environment. In this way the reader is informed as to how pesticides are commonly introduced in to the aquatic environment, reasons as to why it is important to monitor the levels of pesticides, and the fate and behaviour of pesticides. Methods of preconcentration are then illustrated in subsequent chapters. The traditional approach for analyte preconcentration is based on liquid-liquid extraction, LLE. Chapter 3 outlines the theoretical and practical basis for effective LLE. As these traditional approaches invariably use large volumes of organic solvent it is necessary to preconcentrate the extracts further. This is done using one of a variety of solvent evaporation methods (e.g. rotary evaporation, gas blow down, Kuderna-Danish evaporation and EVACS). Finally, the particular case of extraction of volatile organic compounds is illustrated via the technique of purge and trap.

    A modern alternative to LLE is solid phase extraction, SPE (Chapter 4). The principle of SPE is that analyte(s) from a large volume of an aqueous sample can be preferentially retained on a solid sorbent and then eluted with a small volume of organic solvent prior to analysis. The chapter covers the different types of SPE media available, whether in the form of a disk or, more commonly, as a cartridge, method of operation and solvent selection. In addition to preconcentration it is possible to utilise SPE for sample clean-up. The normal mode of operation for SPE is off-line, i.e. the analyte(s) are preconcentrated and then analysed separately. However recent trends, for specific purposes, have seen the introduction of on-line SPE systems directly coupled to either high performance liquid chromatography (HPLC) or gas chromatography (GC). Specific, selected examples are used to demonstrate both the off-line and on-line approaches.

    The final chapter of this section is concerned with the latest development in aqueous sample preconcentration, solid-phase microextraction, SPME (Chapter 5). In this approach a silica-coated fibre is exposed to the sample for a predefined time (sampling), retracted into its protective casing and introduced into either the hot injector of a GC or eluted into an HPLC system using the mobile phase. The former is currently the most common approach. After theoretical and practical descriptions of SPME, selected applications of the use of SPME are reviewed for a range of analyte types (volatile organics, pesticides, phenols). Finally, the versatility of SPME is demonstrated by highlighting the novel approaches to which it has been applied.

    Chapter 6 introduces the background for analysis of pollutants from solid samples. The chapter considers approaches for remediation of soil including containment, treatment and removal. The chapter then goes on to discuss some fundamental questions with regard to environmental analysis of polluted soils: how will you know that total recovery of the pollutant has occurred? What influence does the soil matrix have on the retention of the pollutants? And, which extraction techniques have approved methods? This last question then provides the appropriate technique information for discussion in subsequent chapters.

    Extraction of organic pollutants from solid matrices is traditionally done using liquid-solid extraction, Chapter 7. Liquid-solid extraction can be sub-divided into approaches that utilise heat and those that do not. The use of heat is typified by Soxhlet extraction while the cold extraction methods by sonication or shake-flask. Experimental details for each type of extraction approach are presented as well as selected literature examples of the various liquid-solid extraction procedures. Alternatives to the traditional liquid-solid extraction approaches are focused on instrumental methods, typically supercritical fluid extraction (Chapter 8), microwave-assisted extraction (Chapter 9) and accelerated solvent extraction (Chapter 10). Each of these extraction methods is discussed in terms of instrumentation and theoretical considerations. Environmental applications of each extraction technique are then highlighted with respect to a range of organic pollutants, for example, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phenols and pesticides. Specific emphasis is placed on describing particular features and/or applications of each technique.

    The merits of each extraction technique for either aqueous or solid samples is summarised against a wide range of criteria to provide the reader with an easy-to-read comparison (Chapter 11). Finally, potential future developments for sample preparation are considered in the light of miniaturisation of scientific instruments.

    Dean J.R. (1998) Extraction Methods for Environmental Analysis.

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