Countercurrent liquid/liquid extraction for analysis of organic water pollutants by GC/MS

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A continuous countercurrent liquid/liquid extractor was developed to concentrate trace organic pollutants from large water samples. Non-volatile hydrophobic pollutants were extracted using methylene chloride in a pulsed column system (1 m × 15 mm ID). The procedure follows EPA method 625 to separate the water sample into basic/neutral and acidic compounds. Methylene chloride was chosen from a number of possible solvents (di-isopropylether, chloroform, hexane, ethyl acetate). Solvent efficiencies were studied using ultrapure water containing different model compounds (dimethylphtalate, anthracene, diphenylamine, atrazine, lindane, heptachlor, methyl parathion, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2-chloro,4-nitrophenol). Methylene chloride was found to be the most efficient extractant of both non-polar and polar chemicals. Recoveries ranged between 75% and 96% after one step batch liquid/liquid extraction, except for dimethylphtalate (38%). Pulsed column efficiency was evaluated for a 10 litre ultrapure water sample spiked with the same organic compounds as mentioned above (0.4–1.3 μg/l concentration range). The average recovery was found to be 86%. Continuous countercurrent extractor efficiency was comparable with that observed after a three step batch liquid/liquid extraction. Further, method sensitivity and sample representativity were both improved (concentration factor of 10,000 after 10 litre water extraction). The pulsed column, especially when coupled with GC/MS, can be used to identify trace organic pollutants at the ng/l level in natural waters. Countercurrent liquid/liquid extraction was applied to the analysis of natural surface waters from the Rhône River (France). Results are discussed with regard to EPA and EEC priority lists. Pollutants (such as organochlorine pesticides, triazines, monoaromatic and polyaromatic hydrocarbons, nitrophenols and chlorophenols) were identified by GC/MS at the ng/l level together with several natural organic compounds. Pulsed column extraction can thus be considered as an appropriate multiresidue method for monitoring pollution in natural water.