Soxhlet extractors focused microwave-assisted

As noted earlier, not all open-vessel systems (viz. those that operate at atmospheric pressure) are of the focused type. A number of reported applications use a domestic multi-mode oven to process samples for analytical purposes, usually with a view to coupling the microwave treatment to some other step of the analytical process (generally the determination step). Below are described the most common on-line systems used so far, including domestic ovens (multi-mode systems) and open-vessel focused systems, which operate at atmospheric pressure and are thus much more flexible for coupling to subsequent steps of the analytical process. On the other hand, the increased flexibility of open-vessel systems has promoted the design of new microwave-assisted sample treatment units based on focused or multi-mode (domestic) ovens adapted to the particular purpose. Examples of these new units include the microwave-ultrasound combined extractor, the focused microwave-assisted Soxhlet extractor, the microwave-assisted drying system and the microwave-assisted distillation extractor, which are also dealt with in this section. Finally, the usefulness of the microwave-assisted sample treatment modules incorporated in robot stations is also commented on, albeit briefly as such devices are discussed in greater detail in Chapter 10. 

Focused microwave-assisted Soxhlet extractor The first prototype of a focused microwave-assisted Soxhlet extractor was designed by Luque de Castro et al. and... 

FIGURE 2.17 Automated focused microwave-assisted Soxhlet extractor. (Reprinted from Luque-Garcfa, J. L. and Luque de Castro, M. D., J. Chromatogr. A, 998, 21-29, 2003. With permission from Elsevier.)... 

One useful aspect of microwave systems with open vessels is that they allow direct adaptation of already existing sample preparation methods. Of particular interest for chromatography is the focused microwave-assisted Soxhlet extractor (Figure 2.17 and Figure 2.27). It is based on the same principles as a conventional Soxhlet extractor but is modified to facilitate accommodation of the sample-cartridge compartment in the irradiation zone of a microwave oven. The modification... 

The increased flexibility of open-vessel systems has promoted the design of new microwave-assisted sample treatment units based on focused or multi-mode (domestic) ovens adapted to the particular purpose. Regarding MAE, examples of these new units include the microwave-ultrasound combined extractor and the focused microwave-assisted Soxhlet extractor. 

One of the most interesting fields of application of MAE in food analysis is the extraction of lipids. This step, traditionally performed with conventional Soxhlet extraction, has been performed with the focused microwave-assisted Soxhlet extractor prototype of Figure 2B. Extraction of oil from olives, srm-flower seeds, and soyabeans extraction of the lipid fraction of dairy products (milk and cheese) and extraction of fatty acids from precooked and sausage foods have significant advantages over conventional methods, including dramatically reduced extraction times, lower degradation of thermolabile analytes, and acceleration of other analytical steps such as hydrolysis in milk samples, in addition to completeness of analyte extraction, which is not always achieved with conventional methods. 

The solvent technique for concentrating surfactants is not discussed here. See Ref. [40] for details. Morales-Munoz et al. discuss a screening method for LAS in sediments. It is based on water Soxhlet extraction assisted by focused microwaves. The extractor is coupled with an online preconcentrator/derivatization/detection manifold through a flow injection interface [107]. 

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