Continuous microwave-assisted extraction, solvent changeover and preconcentration of monophenols in agricultural soils

An automatic extraction, preconcentration and clean-up module for the extraction of phenolic compounds from soils was developed; the separation and quantitation of each phenol is accomplished by GC–MS. The sorption–desorption of thirteen phenols on soils containing variable amounts of organic carbon (0.05–3.4%) and clay minerals (2–43%) at pH 5.7–8.6 was investigated. For this purpose, uncontaminated soils were spiked with 5 or 20 μg of each phenol per g of soil; the soils were then stored at 4°C for at least 3 months prior to analysis in order to simulate analyte–matrix interactions other than material losses and environmental degradation in actual contaminated soils. The organic carbon content in acid and alkaline soils affects the sorption of chlorophenols but not that of alkylphenols. On the other hand, alkylphenols are preferentially sorbed by neutral soils, the process being influenced by the clay mineral content. Based on the results, alkylphenols interact more strongly with agricultural soils than do chlorophenols; also, both types of compound are less strongly sorbed by loamy sand soils owing to their increased sand contents.