PCB extraction

The identification of PCB residues in fish, wildlife, and human tissues has been reported since the 1970s (9—13,20—26). The results of these analytical studies led to the ultimate ban on further use and production of these compounds. The precise composition of PCB extracts from biota samples is highly variable and depends, in part, on the specific analyte and the commercial PCB preparations associated with a contaminated area (14). PCBs found in a composite human milk sample from Michigan (26) were highly complex, and the congener composition and their relative concentrations did not resemble any of the commercial PCB preparations. This fact raises obvious problems with regard to the ha2ard assessment of PCB mixtures (27). 

Fig. 4.3. Ultrasonic soil washing, pilot scale equipment giving a 15% improvement in PCB extraction using a Vibrating Tray .

Supercritical fluid extraction conditions were investigated in terms of mobile phase modifier, pressure, temperature and flow rate to improve extraction efficiency (104). High extraction efficiencies, up to 100%, in short times were reported. Relationships between extraction efficiency in supercritical fluid extraction and chromatographic retention in SFC were proposed. The effects of pressure and temperature as well as the advantages of static versus dynamic extraction were explored for PCB extraction in environmental analysis (105). High resolution GC was coupled with SFE in these experiments. 

Many techniques are used for PCBs extraction among them the most used are ... 

By contacting different amounts of sludge and fresh solvent, and allowing equilibrium to establish, information on equilibrium desorption characteristics was gathered. Obviously, increasing the solvent mass to sludge mass ratio (R) will result in an increase in the amount of PCB extracted. It was found that 50% of all extractable PCB desorbed for R approximately equal to 2, whereas 90% of the PCB was removed if R was approximately 5. Similar conclusions were reached for both solvents. 

Note 40 ml of methanol was added to 10 g of sludge sample C. After each cycle, approximately 25 mL of solvent was removed and replaced with fresh solvent. The amoimt of PCB extracted per g of sludge in every cyde is given above. 

Figure 4 Chromatogram of the PCBs extracted from the samples C.3 and C.4 by the common extraction method (purification on Florisil).

Figure 1, Relation between lipid recovery, PCB recovery and the amount basic alumina added to the extraction cell when performing selective PCB extraction...

There are fewer applications of PEE to the extraction of herbicides in soils,being mainly used until now for PAH and PCB extractions. Guzella and Pozzoni performed one of the first successful studies with PEE, by comparing it with Soxhlet procedures on triazine and chloroacetanilide extractions from agricultural soils.A PEE method was developed to extract metribuzin and three metabolites (deaminometribuzin, deaminodiketometribuzin, and diketometribuzin) with methanol-water (75 25) at 60°C. Recoveries were about 75% with detection limits of 1 ng/g, except for diketometribuzin with only 50% of recovery and detection limit higher than 10 ng/g. ... 

Figure 4, Cumulative PCB extraction efficiencies for mobilizations from lOg soil, into scC02 , by sonication (JO minf -washing with 1% ( ), 3% f ) or 5% (m) or by continuous flushing of 30g soil with 1% (o), 3% (o) or 5% (u) aqueous suspension of Triton DF16. (Adapted with permission from reference 13, Copyright 2001, Royal Chemical Society,)...

The analysis of PCBs in various mediums, such as water, soils or oil, is a delicate operation that has been mastered. Gas chromatography with an electron capture detector, which can be coupled in problem cases with a mass spectrometer, is the most suitable method. This article briefly outlined the calculation methods available. The excellent performance of capillary columns call into question current testing standards, which warrant review and revision. Furthermore, the traditional sample preparation methods (i.e., PCB extraction, cleanup, concentration) are evolving and being simplified considerably with the introduction of a wide variety of very specific ready-to-use cartridges. Nevertheless, many tests remain to be performed in this area by laboratories already equipped for PCB analysis so that the effectiveness of their work can be validated. 

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