Dioxin extraction with toluene

SFE has also replaced many regulated solvents in analytical chemistry applications in recent years, primarily because it provides a more reliable measure of the concentrations of environmental contaminants and can play an important role in pollution assessment, abatement, and control. Advantages have been shown for using SFE compared to the conventional Soxhlet extraction with toluene for determining the presence of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in ashes from a municipal incinerator (Dolezal et al., 1995). SFE allows the complete extraction of the analytes from the sample, whereas conventional extraction results in an incomplete, and hence, inferior extraction. 

The DPHSE technique has also been used for the determination of organic pollutants and metals in fly ash and coal, respectively. The extraction of dioxins [48,179] and PAHs [180] from fly ash was accomplished with toluene [48,180] or a toluene-methanol mixture [179], with results as good as or even better than those provided by Soxhiet extraction for 24 h. On the other hand, the extraction of major ash-forming elements (Fe, AI, Ca, Mg, Na and K) [148] and minor inorganic pollutants (As, Se and Hg) [46] from coal was done with acidified water. In the latter case, a combination of static and dynamic extraction was found to provide quantitative recoveries within a shorter time and with less dilution of the extracts than dynamic extraction alone. Acidified water is more corrosive than pure water, so the high temperatures required for extraction (150-200°C) call for the use of an extractor made of a material more corrosion-resistant than steel hastel-loid. However, in proportions above 4%, nitric acid — the acidulant most frequently added to the water — has been found to result in clogging of the system and the restrictor, so the recommended acid concentration is much lower than that. 

SEE has so far been the technique most frequently used to validate DPSE methods such as those for the extraction of dioxins from high- and low-carbon fly ash [48], triazolo-pyrimidine sulphonanilide herbicides, trichloropyridinol and PCBs from soil [150,152, 168], and carotenoids and tocopherol from spice red pepper [177]. As noted earlier, neither technique can be said to be better than the other it depends on the characteristics of the analytes to be extracted (e.g. on their polarity and high-temperature stability). Thus, in the extraction of cloransulam-methyl from soil, while the use of subcritical water provided higher recoveries than SEE, the analyte was not hydrolytically stable above 150°C, which entailed using a lower temperature and hence an increased extraction time [152]. In the extraction of PAHs from bituminous coal fly ash [180], extraction with supercritical CO, yielded better recoveries than DPHSE using toluene and methylene... 

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