A multivariate optimization scheme (MOS) was used to investigate the effects of environmental variables and supercritical fluid extraction (SFE) parameters on the extractability of pesticide residues from soil samples. MOS is a highly efficient technique for studying a large number of variables and identifying optimal extraction conditions. MOS offered the opportunity to systematically and simultaneously examine the interaction and effect profiles among important soil variables and extraction parameters. Pesticide residence time in soil had a major influence on binding extent for all tested pesticides. Extractability as a function of soil composition was greatly dependent on the particular pesticide examined. Bensulfuron-methyl was the most difficult to extract from soils containing high levels of both organic matter and clay. Atrazine was extracted more easily than diuron. High organic matter and high clay content led to strong binding for diuron and atrazine, respectively. Effects of SFE parameters on extractability appeared to depend on the nature of residues (e.g., freshly fortified versus aged residues). For freshly fortified samples, analyte solubility in supercritical fluid and/or modified supercritical fluid was the critical factor as indicated by the strong influence of pressure on extraction efficiency. For aged samples, temperature was an important determinant of extraction efficiency, indicating that mass transfer or diffusion processes were rate-limiting. The presence of modifier and extraction duration also significantly impacted extractability of aged pesticides.
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Zhou et al. (1997) studied this question.