MICROWAVE-ASSISTED EXTRACTION OF ORGANIC-COMPOUNDS FROM STANDARD REFERENCE SOILS AND SEDIMENTS

As part of an ongoing evaluation of new sample preparation techniques by the U.S. Environmental Protection Agency (EPA), especially those th at minimize waste solvents, microwave-assisted extraction (MAE) of org anic compounds from solid materials (or ''matrices'') was evaluated. S ix certified reference materials containing polynuclear aromatic hydro carbons (PAHs) and a few base/neutral/acidic compounds all of which ar e common pollutants of interest to the EPA were subjected to MAE in a closed-vessel microwave system with hexane/acetone (1:1) at different temperatures (80, 115, and 145-degrees-C) and for different periods of time (5, 10, and 20 min). For comparison, the same samples were subje cted to room-temperature extraction by allowing the solvent mixture to stay in contact with the solid matrix the same amount of time as the microwave-extracted sample (including any cooling time). Whereas the a verage recovery at room temperature was approximately 52%, the MAE rec overies for the 17 PAHs (3 of which were deuterated PAHs that were spi ked into these matrices) from the six matrices were 70% at 80-degrees- C, 75% at 115-degrees-C, and 75% at 145-degrees-C. Although the averag e recoveries increased slightly with extraction time, the increase was not statistically significant. The performance of the technique varie d with the matrix and the analyte. Eleven PAHs had average recoveries in the 65-85% range, and three compounds (acenaphthene, benzo[a]pyrene , and fluorene) had recoveries of approximately 50%. The spiked-compou nd recoveries were 77% for acenaphthene-d10, 105% for fluoranthene-d10 , and 85% for benzo[a]anthracene-d12. Experiments with 14 phenols and 20 organochlorine pesticides indicated that MAE is a viable alternativ e to the conventional Soxhlet/Soxtec and sonication techniques. The MA E technique requires smaller amounts of organic solvents, and sample t hroughput is increased by shorter extraction times (10 min) and by sim ultaneous extraction of up to 12 samples.