Evaluation of supercritical fluid extraction, microwave-assisted extraction and sonication in the determination of some phenolic compounds from various soil matrices

Extraction methods using supercritical fluid extraction (SFE) and microwave-assisted process (MAP) techniques, with or without a one-step in situ derivatisation, were evaluated for the extraction of phenol, o-cresol, m-cresol and p-cresol from soils. Five artificially spiked soil matrices were prepared; three of them were prepared by adding various amounts of activated charcoal in order to increase the degree of analyte-matrix interaction. We also applied the methods to a real phenol contaminated soil with a high carbon content (18%). To provide a basis for comparison, all the soils were extracted using an US Environmental Protection Agency-approved sonication protocol. The extracts obtained were analyzed on a GC-MS system without any preliminary clean-up or concentration steps. The results showed that SFE and MAP are more efficient than sonication with at least twice the recovery in all the soils tested. MAP and MAP-derivatisation showed the best recoveries (>80%) for the five spiked matrices studied with the exception of o-cresol in soils with activated charcoal content higher than 5%. In these specific soils, SFE showed very low recoveries for the four phenols. However, recoveries were significantly improved when a derivatisation step was combined to SFE. In the real soil tested, the recoveries using derivatisation-extraction process were lower than the recoveries using extraction process. In general, derivatisation-extractions perform better and do not require extreme extraction conditions.