Automation and improvement of steps subsequent to DPHSE

The most analytically unfavourable feature of DPHSE is that analytes are diluted in the liquid extract, which requires concentration (usually by static liquid-liquid or solid-phase extraction). However, the increased flexibility of DPHSE relative to ASE has been used to develop various approaches to the partial or complete automation of methods based on the use of hyphenated techniques. Such approaches not only allow the dilution problem to be overcome but also enable automation and/or facilitate the development of other steps of the analytical process such as filtration, detection or chromatographic separation. The principal approaches to automation and improved implementation of analytical steps subsequent to DPHSE are discussed below. 

Extraction discs placed directly over the exit frit of the extraction cell have been used for the preconcentration of highly water-soluble acidic compounds from soil [39]. A strong anion-exchange (SAX) sorption disc facilitated not only preconcentration but also derivatization of the analytes. 

Miniaturized retention has been accomplished by using solid-phase microextraction (SPME) to collect PAHs from soil, air particulate matter and urban particulates [62,165], and pyrethrins from pyrethrum flower [165] in the fibre after quantitative extraction with superheated water [62,166]. 

One very common, undesirable occurrence in DPHSE is the presence of solid particles in the liquid extract due to oversaturation during cooling. This shortcoming can be circumvented by fitting a filtration unit in-line with the extractor the unit can be placed 

High-pressure, high-temperature solvent extraction 

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