Specific Applications for MAE

Selected MAE applications are identified in Table 3. Polycyclic Aromatic Hydrocarbons (PAHs)

Work done by V. Lopez-Avila et al. indicated that PAHs, with the exception of more volatile compounds such as naphthalene, can be extracted quantitatively (recovery > 80%) from soil and sediment matrices with hexane-acetone (1 : 1) at temperatures of 115°C. Typical extraction times for batches of up to 12 samples (5 g each) are 10 min at 100% power (1000 watts). The lower recoveries of naphthalene, acenaphthene, and acenaphthylene were attributed to the presence of water in the soil matrix (to prepare a representative aged soil sample, water was added to the soil matrix to bring its water content to 30%).

Other successful microwave-assisted extractions of PAHs from soils, sediments, and fly ash have been reported with hexane-acetone (1 : 1), acetone alone, dichloromethane alone, dichloromethane-toluene (50 : 50), acetone-petroleum ether (1:1), methanol-toluene (9 : 1), and toluene-water.

Dean et al. reported on a direct comparison between Soxhlet, MAE, and SFE for PAHs and concluded that the major advantage of MAE is the speed of extraction, but they also acknowledged that without additional cooling after extraction it takes approximately 30 min until the vessels can be opened and extracts processed. Barnabas, Dean and coworkers also investigated the effects of pressure, temperature, extraction time, and percent of methanol modifier added to the extraction solvent in order to optimize the extraction.

Chee et al. reported a 5-min heating at 115°C with 30 mL hexane-acetone (1:1) as the optimum extraction conditions for a 5 g sample, conditions which are very similar to those reported by V. LopezAvila et al.

Optimization of MAE of PAHs using open-vessel technology was conducted by Budzinski et al., who reported that the optimum conditions are 30% water, 30 mL dichloromethane, and 10 min heating at 30 W power. When considering that the time needed to reach the boiling point is about 2 min (for dichloromethane), a heating time of 10 min is more than sufficient to extract PAHs quantitatively from the matrix, especially when adding water which is supposed to cause swelling of the matrix.

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