Applications of DPHSE

Like ASE, pressurized hot solvent extraction has been virtually exclusively applied to solid samples. There is only a single reported use with liquid samples that involved altering the extractor and is dealt with separately at the end of this section on account of its innovative character. As in ASE, most applications are concerned with environmental samples there are however, several interesting uses in the biological field. This section discusses the more interesting applications of DPHSE in terms of the matrix types and analytes involved. 

The extraction of inorganic species such as Fe [146], and Cu, Pb, As, Se, Hg and Cd [172], from soils was investigated on a pilot plant scale with a view to developing an industrial-scale method for decreasing allowed levels of the metals used to manufacture cement. To this end, kinetic curves for the extraction rate were used that allowed the time 

High-pressure, high-temperature solvent extraction 

In many of the previous applications, a combination of static and dynamic extraction was found to reduce the extraction time and provide better recoveries. Such is the case with the extraction of linear alkylbenzenesulphonates [24] and 4-nonylphenols [25] from sediments, and that of PAHs from soil [47], where a combination of 15 min static extraction and 10-20 min dynamic extraction ensured quantitative extraction of the analytes, thus minimizing the dilution effect arising from extended dynamic extraction. 

Pure water at a high pressure and temperature was the solvent used as extractant in most applications. However, the addition of a modifier [157,173] or a co-extractant [47] can dramatically improve the extraction of some substances. Such is the case with the extraction of nonylphenol polyethoxy carboxylates from industrial and municipal sludges, where recovery was increased by more than 30% in the presence of 30% (v/v) ethanol in the water used as leaching agent [157]. Because of the hydrophobic nature of PAHs, the increased dielectric constant of water at a high temperature did not suffice to ensure quantitative extraction from soil. However, as can be seen from Fig. 6.14, the addition of a co-extractant (viz. sodium dodecyl sulphate, SDS, which forms charged micelles) dramatically improved the extraction of these hydrophobic compounds also, it substantially reduced the extraction time and enabled the quantitative recovery of benzo(a)-acenaphthene [47]. 

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As can be seen from Fig. 6.9, dynamic pressurized hot solvent extraction (DPHSE) has evolved similarly to ASE however, as noted earlier, DPHSE has been the subject of many fewer reports, primarily as a result of the lack of commercially available equipment for implementation. In any case, the relatively scant reported applications of DPHSE are of especial interest as regards automation of the analytical process in fact, the dynamic nature of the system facilitates its coupling to other dynamic systems with a view to accomplishing preconcentration [39,42,45,145], filtration [42,45], chromatographic separation [145,146], derivatization [46,57] and detection [44,147], among others, and the partial or total automation of the analytical process. 

Because of the above-stated lack of commercially available DPHSE equipment, applications of the dynamic extraction mode have all been developed using laboratory-built configurations that comprise the following basic elements ... 

As with ASE, the advantages and disadvantages of DPHSE with respect to MAE and SEE are not so clear and depend on the particular application. 

One of the few DPHSE applications using an extractant other than water is that involving the extraction of spice red pepper oil with subcritical propane for the determination of the carotenoid and tocopherol contents [177]. 

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