Effect of extraction temperature on pressurized liquid extraction of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls from a sediment sample using polar and non-polar solvents

This study is the first to investigate the effect of extraction temperature (150, 175, and 200 °C) on the simultaneous pressurized liquid extraction (PLE) of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) from a sediment sample (certified reference material: JSAC 0431). To provide basic data that will help to determine the optimum conditions for PLE, six single solvents (toluene, dichloromethane [DCM], benzene, acetonitrile, acetone, and methanol) were used as an extraction solvent. The results obtained by PLE with each solvent were compared with those obtained by Soxhlet extraction using toluene. The efficiency of PLE for 2,3,7,8-substituted PCDDs, 2,3,7,8-substituted PCDFs, and DL-PCBs, as obtained by PLE using the solvents toluene, DCM, benzene, and acetonitrile, showed an increase with increasing extraction temperature. The recoveries of PCDDs, PCDFs, and DL-PCBs obtained by PLE using toluene were similar to or inferior to those obtained using the Soxhlet method. In contrast, their recoveries obtained by PLE using DCM, benzene, and acetonitrile were similar to or higher than those obtained using the Soxhlet method. Notably, the recoveries of PCDDs, PCDFs, and DL-PCBs using benzene at 200 °C were 117 ± 15, 123 ± 13, and 115 ± 12%, respectively. When using acetone and toluene, the recoveries of tetra–hexaCDDs and tetra–hexaCDFs also increased with extraction temperature. In particular, the recoveries of 2,3,7,8-tetraCDD and 2,3,7,8-tetraCDF obtained with acetone at 200 °C were 181 ± 21 and 167 ± 14%, respectively. However, the efficiency of PLE for heptaCDDs and/or heptaCDFs was insufficient at all the tested temperatures. Furthermore, the efficiency of PLE for octaCDD and/or octaCDF showed a pronounced decrease with increasing extraction temperature, yielding recoveries of approximately 40% at 200 °C. We found that heptaCDF isomers were produced from authentic octaCDF during the PLE procedure with acetone at 200 °C, indicating that the lower recoveries of highly chlorinated DDs and/or DFs are attributable to their degradation.