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A method for the prediction of a suitable solvent for the extraction of pesticides is outlined. The procedure is based on the Hildebrand solubility parameter, delta(t). The solubility parameter is broken down into three individual components, which are calculated by the addition of group contributions. To demonstrate the applicability of the approach pressurized fluid extraction was used to extract 4,4'-DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and its metabolites, 4,4'-DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] and 4,4'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene], from an historically contaminated soil from the United States and pentachlorophenol from a certified reference material (CRM524) using various solvents. Visual representation of the individual parameters predicted the ideal extraction solvent to be DCM for 4,4'-DDT and its metabolites and a mixture of acetonitrile and dichloromethane (1:1, v/v) for PCP. These findings were confirmed by the experimental results.

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Pressurised fluid extraction (PFE) of polycyclic aromatic hydrocarbons (PAHs) from a certified reference material (CRM) 524 has been firstly optimised following a central composite design. The instrumental parameters of the PFE (pressure, temperature, extraction time and number of solvent cycles) were studied in order to obtain maximum extraction yields. Neither pressure nor extraction time or temperature seemed to have any significant effect on the extraction yield, therefore one extraction cycle was enough to exhaustively extract all the PAHs from CRM 524. Once the instrumental conditions were established, the extraction yields obtained with eight different solvents or solvent mixtures [acetone, dichloromethane, acetonitrile, acetone-dichloromethane (1 + 1 v/v), acetone-isohexane (1 + 1 v/v), isohexane, methanol and toluene] from the CRM 524 were compared and showed that the best recoveries were obtained with acetone-isohexane (1 + 1 v/v). Finally, the effect of sand, silt, clay and the organic matter content of soil was investigated with respect to recovery of PAHs by PFE with different solvents or solvent mixtures for aged soil samples. In this case, eight soils with different sand, silt, clay and organic matter contents were slurry spiked with PAHs and aged for 19 days. Three aliquots of each slurry spiked soil were extracted with the previously mentioned solvents and the results were studied by means of principal component analysis (PCA) of the whole data set (soil composition, solubility parameter of the solvent and recoveries of all PAHs) and partial least squares (PLS). Clay and organic matter content and the squared solubility parameter have the highest correlation with the recovery of PAHs from soil samples.