Optimisation of the microwave-assisted extraction in open cell of polycyclic aromatic hydrocarbons from soils and sediments - Study of moisture effect

Sample preparation remains a long and critical step for organic contaminant analyses in the environment. Classical extraction methods, like Soxhlet ex traction, are time and solvent consuming. Some new techniques have been dev eloped in the last few years (supercritical fluid extraction, microwave-ass isted extraction, pressurized liquid extraction). Among them, microwave-ass isted extraction at atmospheric pressure has appeared an interesting altern ative method to Soxhlet extraction. In this present study the extraction of polycyclic aromatic hydrocarbons (PAHs) from solid environmental matrices (soils and sediments) by a microwave-assisted method has been studied. In a first part the experimental conditions have been optimised and different p arameters adjusted using the SRM 1941a as a test matrix: time and power of irradiation, nature of solvent, percentage of water. Among all the paramete rs, the quantity of water is of primary importance to maximize the recoveri es. With the optimised conditions applied to the SRM 1941a, the results obt ained by the microwave-assisted extraction with 30% of water are in a good agreement with those obtained by Soxhlet. When compared to the certified va lues, the global recovery obtained by microwave-assisted extraction with 30 % of water is 90%. The relative standard deviations obtained for the microw ave-assisted extraction with 30% of water are in the same range as those gi ven by the Soxhlet extraction and in good agreement with the certified valu es (relative standard deviations below 15%). The optimal conditions (30% of water, 30 mi of dichloromethane, 30 W, 10 min) have then been applied to t he extraction of PAHs from various matrices (certified and natural ones; so ils, sediments, sewage sludge) and the concentrations of PAHs obtained by m icrowave-assisted extraction are compared to those obtained by Soxhlet extr action. For all the samples tested in this study the recoveries for the mic rowave-assisted extraction using 30% of water are very good (more than 85%) in comparison to the Soxhlet extractions. The reproducibility of such an o ptimised procedure is also very correct (under 15% for I;PAHs for all the m atrices). The method developed has appeared to be not matrix-dependent. (C) 1999 Elsevier Science B.V. All rights reserved.