DPHSE devices

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  

The ovens used in DPHSE range from those for supercritical fluids [39,150,151] to gas chromatographic models [42,82] to specially designed units [75,146,148,152]. 

The extraction cell is preceded by a pre-heater intended to ensure that any solvent reaching the cell comes into contact with the sample at the oven temperature. Coils of variable length and empty extraction chambers have been used as pre-heaters. The presence of one is especially important with high extractant flow-rates the length of the coil or the volume of the empty cell used should ensure that the solvent resides in them for long enough to reach the oven temperature before it enters the extraction cell. 

High-pressure, high-temperature solvent extraction 

The extraction cells used in DPHSE include those typically employed in SFE [109,151], empty HPLC columns [149] and specially designed stainless steel chambers [57,75,148]. The use of an SFE chamber as extraction cell is not recommended because the polyimide seals in it can fail at high temperatures [6]. On the other hand, the problem with empty HPLC columns is that they usually have small diameters and hence low volumes — this can result in excessive pressure build-up and bursting of the column. As a rule, DPHSE extraction cells consist of a stainless steel cylinder closed with screws at either end that permit the circulation of the leaching solvent through them. The screw caps also contain stainless steel filter plates to ensure that the sample remains in the extraction chamber. 

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Fig. 6,12. Miniaturized device for DPHSE of solid and semi-solid samples. (Reproduced with permission of Elsevier.)...

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