Polychlorinated biphenyls (PCBs) are representative persistent organic pollutants and suspected to be endocrine disrupters. Although PCBs have been removed from production and use in Japan since the early 1970s, they still remain in the environment. One of the major environmental sinks for PCBs is the sediment matrix, and thus the accurate quantification of trace PCBs in this matrix is important for evaluating their risk.In general, the quantification of PCBs in the sediment includes three analytical processes: the extraction of PCBs from the sediment, cleanup of the extracts, and analysis by gas chromatography (GC) with either mass spectrometry (MS) or electron-capture detection. The classical extraction methods, such as Soxhlet extraction 1,2 and saponification, followed by solvent extraction, 3 are usually applied as extraction techniques, but these methods are time-consuming and require a large amount of organic solvents. Supercritical fluid extraction (SFE) can possibly overcome these disadvantages. 4 A number of articles have appeared on the SFE of PCBs from sediments. Compared with Soxhlet extraction, SFE can provide a comparable or higher extraction efficiency. [5][6][7][8][9] However, the recovery yields of PCBs by SFE were significantly affected by various operating parameters, including the extraction temperature, [6][7][8][9][10][11][12][13] extraction pressure 8,9,12-14 and modifier addition. 8,9,[14][15][16][17] Therefore, optimization of the SFE conditions is very important for the accurate quantification of PCBs in sediments.Isotope dilution mass spectrometry (IDMS) has potential to be operated as a primary method of measurement. 18 Accurate quantification of PCBs may be expected when the IDMS technique is applied with GC-MS. However, equilibration between isotope-labeled compounds added as internal standards and native analytes in the sample is a prerequisite in the IDMS technique. The results from ID-GC-MS would show an incorrectly low amount of PCBs if equilibration is not achieved, as would occur if the quantitative extraction of analytes from a solid matrix is not achieved.
19Therefore, highly efficient extraction is required for the accurate quantification of PCBs in sediments, even if isotope-labeled PCB congeners are used as internal standards.The National Metrology Institute of Japan (NMIJ) has developed two kinds of marine sediment certified reference materials (CRMs) to be used for the validation of PCB quantification. [20][21][22] In the certification process, five kinds of independent extraction methods were applied for IDMS quantification to avoid any possible procedural bias. For that purpose, we developed four accurate extraction methods for PCBs in sediments in advance. We developed pressurized liquid extraction 23,24 and microwave-assisted extraction 25 as extraction techniques for the IDMS quantification. A method of saponification, followed by solvent extraction, was also optimized to give higher recovery yields of PCB congeners.
26SFE is another extraction technique we have d...