Extraction of polycyclic aromatic hydrocarbons from polluted soils with binary and ternary supercritical phases

Supercritical fluid extractions (SFE) using carbon dioxide and modifiers (n-hexane, cyclohexane, toluene, methyl tert.-butyl ether, methoxybenzene, dichloromethane, propanone, pyridine, methanol) as well as modifier mixtures (methanol-containing diethylamine, 2-aminoethan-1-ol, acetic acid) were performed to extract polycyclic aromatic hydrocarbons (PAHs) from real environmental samples polluted to a minor extent by mineral oil products and highly contaminated by brown coal tar. Comparing the results with those from Soxhlet extraction utilizing dichloromethane and SFE using pure carbon dioxide show that acidic or basic co-solvents give the highest PAH yields in all cases. Extraction efficiency decreases with reduced polarity of the modifier used and increases at higher concentrations of co-solvent. To explain the SFE results we discuss several mechanisms of disruption of matrix-PAH interactions: first the competition between the modifier molecules and the active sites of soil's organic and inorganic matter to interact with non-covalent bondings to the analytes; and second the splitting of electron donor-acceptor complexes between humic substances and PAHs induced by Lewis acids or Lewis bases. (C) 1997 Elsevier Science B.V.