Supercritical fluid extraction with solid-phase trapping of chlorinated and brominated pollutants from sediment samples

Abstract

Trapping efficiencies for selected polychlorinated benzenes, polybrominated biphenyls and polybrominated diphenyl ethers were studied to determine the trapping capability of these and similar compounds in real samples. A study was made of the effect on recovery of supercritical fluid extraction (SFE) temperature, pressure, flow-rate, addition of modifier, types of solid phase trapping material and elution parameters. Florisil and ODS, used as trapping materials, both produced satisfactory recoveries (>95%) for most compounds under optimised conditions, but the performance of Florisil was less dependent on SFE flow-rate. At higher flow-rates, ODS gave lower recoveries of the chlorinated benzenes and it generally could not trap the dichlorobenzenes, which Florisil recovered up to 95%. When pure CO 2 was used at constant flow-rate, change in the SFE conditions did not significantly affect the trapping efficiency. Experiments with modifiers showed good recoveries with a trap temperature close to or above the boiling point of the modifier. Sequential SFE was applied to extract chlorinated and brominated organic pollutants from nine sediments. 80%–95% of the total SFE recovery was obtained with CO 2 alone, and further recovery with addition of modifier. The recovery varied with the sediment, indicating that the usefulness of the modifier depends on the sample matrix. Altogether, 46 analytes were quantified in the sediment extracts in one run at levels down to 10 pg/g using two-channel GC with electron-capture detection. Polychlorinated biphenyls and common pesticides such as p,p′-DDE, p,p′-DDD and p,p′-DDT were found to be the most abundant pollutants in all sediment samples. Polybrominated aromatic compounds also were found in all samples, with the highest levels for dibromodiphenyl ether, polybrominated biphenyl 52, pentabromodiphenyl ether, 2,3,7,8-tetrabromodibenzo- p-dioxin and 2,3,4,7,8-pentabromodibenzofuran. Levels in Baltic Sea area sediments were in the low ppb (ng/g) range. The use of two capillary columns of different polarity greatly decreased the number of errors arising from coeluting compounds.