Pressurized liquid and accelerated solvent extraction Ple Ase

PLE encloses a number of extraction techniques that use solvents at elevated temperatures and pressures. Best known is ASE that originates from SFE and uses organic solvents at high temperature and high pressure to leach out the organics from solid matrixes. Compared to extractions at or near room temperature and at atmospheric pressure, ASE delivers enhanced performance by the increased solubility, the improved mass transfer and the disruption of surface adsorption by the conditions applied. Dionex Corp. introduced in 1995 a fully automated sequential extraction system that was very soon after its introduction recommended by the US Environmental Protection Agency (EPA) for the extraction of solid waste [25]. Typical conditions for an ASE extraction are: temperature 100°C, pressure 2,000 psi, extraction time 5 min equilibration and 5 min static extraction with a solvent composed of dichloromethane and acetone in ratio 1:1. The speed of the extraction process is greatly increased compared to conventional liquidsolid methods and virtually all organics can be extracted. Disadvantages of ASE are the lack of selectivity which means that further clean-up is needed and that the sample is too dilute for direct analysis and further concentration is required. Recent developments to circumvent these shortcomings are the combination of ASE with SPE and the application of large volume injection.

The application of PLE for food (and biological) sample analysis has been reviewed by Carabias-Martinez et al. [26]. Recent applications include the determination of ochratoxin in bread [27] and bisphenol A diglycidyl ether in canned food [28].

Another variant of PLE is extraction at high temperatures and pressures with water. Super-heated water extraction (SHWE) including many applications was recently reviewed by Smith [29]. Although SHWE is by far the most ''green'' extraction technique, main disadvantages of SHWE over ASE are that the solutes are obtained in dilute aqueous medium and further extraction with an organic solvent is required. A large number of matrix compounds are extracted as well, so that further clean-up is needed and last but not least that the thermal stability of the target solutes under SHWE conditions should be carefully evaluated.

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