Microwave-assisted extraction and accelerated solvent extraction with ethyl acetate-cyclohexane before determination of organochlorines in fish tissue by gas chromatography with electron-capture detection

Focused open-vessel microwave-assisted extraction (FOV-MAE), closed-vessel microwave-assisted extraction (CV-MAE), and accelerated solvent extraction (ASE) were used for extraction before determination of organochlorine compo unds (polychlorinated biphenyls, DDT, toxaphene, chlordane, hexachlorobenze ne, hexachlorocyclohexanes, and dieldrin) in cod liver and fish fillets. We t samples were extracted without the time-consuming step of lyophilization or other sample-drying procedures. Extractions were performed with the solv ent mixture ethyl acetate-cyclohexane (1 + 1, v/v), which allowed direct us e of gel-permeation chromatography without solvent exchange. For FOV-MAE, t he solvent mixture removed water from the sample matrix via azeotropic dist illation. The status of water removal was controlled during extraction by m easuring the temperature of the distillate. After water removal, the temper ature of the distillate increased and the solvent mixture became less polar . Only the pure extraction solvent allowed quantitative extraction of the o rganochlorine compounds. For CV-MAE, water could not be separated during th e extraction. For this reason, the extraction procedure for wet fish tissue required 2 extraction steps: the first for manual removal of coextracted w ater, and the second for quantitative extraction of the organochlorine comp ounds with the pure solvent. Therefore, CV-MAE is less convenient for sampl es with high water content. For ASE, water in the sample was bound with Na2 SO4. The reproducibility for each technique was very good (relative standar d deviation was typically <10%); the slightly varying levels were attribute d to deviations during sample cleanup and the generally low levels.