Hyphenated techniques Subject

Atomic absorption remained the technique of choice until relatively recently. However, with the introduction of plasma sources, atomic emission, in the form of inductively coupled plasma spectroscopy, has made a comeback. This development is now receiving historical attention, and was the subject of a symposium held in 1999. Papers discussed atomic emission analysis prior to 1950,206 the fact that emission techniques developed continuously, even in the period when absorption methods were dominant,207 and the development of the plasma sources on which the new techniques depend.208 Also discussed was the powerful hyphenated technique of ICP-MS,209 and the history of one of the leading manufacturers of atomic emission instruments.210... 

The possibility of combining separation and detection techniques gives origin to the so-called hyphenated-techniques , analytical systems able to answer these questions. Well described approaches on the subject are in the special issue of Spectrochimica Acta devoted to Speciation [111]. 

The objective of this symposium and this book is to acquaint the readers with the latest advances in the field of elemental analysis and to focus on what avenues of future research to explore in this area. The subjects included are various elemental analysis techniques such as atomic absorption spectrometry, inductively coupled plasma emission and mass spectrometry, isotope dilution mass spectrometry. X-ray fluorescence, ion chromatography, gas chromatography-atomic emission detection, other hyphenated techniques, hetero-atom microanalysis, sample preparation, reference materials, and other subjects related to matrices such as petroleum products, lubricating oils and additives, crude oils, used oils, catalysts, etc. 

Each chapter provides a discussion of the fundamental principles underlying the techniques, descriptions of the instrumentation, and numerous applications. The chapters also contain updated bibliographies and problems, and most have suggested experiments appropriate to the techniques. This completely revised and updated edition covers subjects in more detail, such as a completely revised x-ray chapter, expanded coverage of electroanalytical techniques, and expansion of chromatography and mass spectrometry topics to reflect the predominance of these instruments in laboratories. This includes state-of-the-art sample introduction and mass analyzers and the latest developments in UPLC and hyphenated techniques. The book also contains new graphics and addresses several new topics ... 

By considering in situ characterization of the deposits, hyphenated techniques can represent very important tools to enrich the picture of the coating when subjected to electrochemical polarization. In this case, the electrochemical stimulus, in terms of either potential or current applied to the system, is coupled to a direct observation of the modification induced. UV-visible and Raman spectroelectrochemistry were and still are infi equently used to simultaneously... 

Off-line techniques (as opposed to online coupling or hyphenated techniques) have the particular advantage that samples can be processed in parallel and the extracts can be subjected to other analytical processes besides GC-MS. Online techniques have the special advantage of sequential processing of the samples without intermediate manual steps. The online clean-up allows an optimal time overlap which gives the sample preparation the same amount of time as the... 

Combining separation and analysis techniques (hyphenated techniques) can produce powerful tools for chtiracteriz-ing viscous oils. Thus, liquid chromatography or gas chromatography can be used to separate a sample for subsequent characterization by mass spectrometry (LC/MS or GC/MS). Research into suitable methods for the analysis of viscous oils is underway, but no standard tests have yet been prepared. Extensive research on both proton and carbon-13 nuclear magnetic resonance spectroscopy shows promise as a tool for the analysis of lubricant base oils and other viscous oils. Both near-infrared spectroscopy (NIR) and Fourier-transform IR (FTIR) are the subjects of active research into methods to characterize hydrocarbons and for quality control during production of petroleum products. Standard test methods using these techniques should become available in the future. 

The combination of chromatography and mass spectrometry (MS) is a subject that has attracted much interest over the last forty years or so. The combination of gas chromatography (GC) with mass spectrometry (GC-MS) was first reported in 1958 and made available commercially in 1967. Since then, it has become increasingly utilized and is probably the most widely used hyphenated or tandem technique, as such combinations are often known. The acceptance of GC-MS as a routine technique has in no small part been due to the fact that interfaces have been available for both packed and capillary columns which allow the vast majority of compounds amenable to separation by gas chromatography to be transferred efficiently to the mass spectrometer. Compounds amenable to analysis by GC need to be both volatile, at the temperatures used to achieve separation, and thermally stable, i.e. the same requirements needed to produce mass spectra from an analyte using either electron (El) or chemical ionization (Cl) (see Chapter 3). In simple terms, therefore, virtually all compounds that pass through a GC column can be ionized and the full analytical capabilities of the mass spectrometer utilized. 

Table 10.32 is a shortlist of the characteristics of the ideal polymer/additive analysis technique. It is hoped that the ideal method of the future will be a reliable, cost-effective, qualitative and quantitative, in-polymer additive analysis technique. It may be useful to briefly compare the two general approaches to additive analysis, namely conventional and in-polymer methods. The classical methods range from inexpensive to expensive in terms of equipment they are well established and subject to continuous evolution and their strengths and deficiencies are well documented. We stressed the hyphenated methods for qualitative analysis and the dissolution methods for quantitative analysis. Lattimer and Harris [130] concluded in 1989 that there was no clear advantage for direct analysis (of rubbers) over extract analysis. Despite many instrumental advances in the last decade, this conclusion still largely holds true today. Direct analysis is experimentally somewhat faster and easier, but tends to require greater interpretative difficulties. Direct analysis avoids such common extraction difficulties as ... 

As liquid chromatography plays a dominant role in chemical separations, advancements in the field of LC-NMR and the availability of commercial LC-NMR instrumentation in several formats has contributed to the widespread acceptance of hyphenated NMR techniques. The different methods for sampling and data acquisition, as well as selected applications will be discussed in this section. LC-NMR has found a wide range of applications including structure elucidation of natural products, studies of drug metabolism, transformation of environmental contaminants, structure determination of pharmaceutical impurities, and analysis of biofiuids such as urine and blood plasma. Readers interested in an in-depth treatment of this topic are referred to the recent book on this subject [25]. 

Thermal analysis is a group of techniques in which a physical property of a substance is measured as a function of temperature when the sample is subjected to a controlled temperature program. Single techniques, such as thermogravimetry (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric thermal analysis, etc., provide important information on the thermal behaviour of materials. However, for polymer characterisation, for instance in case of degradation, further analysis is required, particularly because all of the techniques listed above mainly describe materials only from a physical point of view. A hyphenated thermal analyser is a powerful tool to yield the much-needed additional chemical information. In this paper we will concentrate on simultaneous thermogravimetric techniques. 

While the benefits of flow-based methods such as the reduction of the analysis time and higher sample throughput are greatly appreciated in the analytical sciences, their applications in the determination of parabens are greatly limited. For comparison, flow-based techniques are widely applied in the analysis of other preservatives such as sulfites and nitrites [30,31]. Thus, more investigations and publications on this subject are called for. The applications of this technique in the analysis of foodstuffs are limited to simple techniques such as flow injection and sequential injection analysis. However, the use of novel hyphenated flow-based techniques would bring about a breakthrough in the determination of parabens in various consumer products. Moreover, there should be a shift to the use of mass spectrometric detectors from the selective detectors such as chemiluminescence and UV-Vis. 

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