Liquid Liquid Extraction LLE

LLE consists of partitioning of an analyte from water into an immiscible solvent. LLE of organic contaminants from water samples is very much on the decline as a preconcentration technique. This is due to the fact that large volumes of toxic organic solvents, such as methylene chloride, are needed, which creates an expensive waste stream and unnecessarily exposes laboratory workers to hazardous fumes. Furthermore, developments in separation technology have provided several superior methods for use today. Nevertheless, LLE is still being applied to the extraction of PAHs from water samples and an EPA Method still exists for its use.

EPA Methods 610 and 3510C82'83 are available for LLE of PAHs from water and wastewater samples. Large volumes of sample are collected, acidified to pH < 2, and frozen. For extraction, 1l of sample is spiked with surrogate standards and extracted three times with 60 ml of DCM. The extract is dried by passing through a column of anhydrous sodium sulfate and rotary evaporated to concentrate the sample prior to GC analysis. If HPLC analysis is desired, the solvent is exchanged with ACN. LLE was used to measure PAHs in surface water and runoff in western Nigeria,84 where there is no central sewer system and discharges are directed into the rivers during the rainy season. Very low recoveries for the more volatile PAHs were observed, 11% for naphthalene; average corrected recoveries were 89%. Reported measured concentrations were 0.10 to 73.72 mg 1"1 of predominantly three- and four-ring PAHs. Water samples, from the Izmit Bay in Turkey, on the east side of the Sea of Marmara, were extracted with HEX and analysis was performed by HPLC-FLD.85 Of 17 PAHs measured, PHN was the most abundant compound followed by CHR both at around 1 ng 1"Water concentrations measured were 1000 times lower than concentrations measured in mussels. Reported detection limits were 0.55 to 0.004 ng 1"Almost all PAHs detected were the smaller, more water-soluble ones from NAP to CHY. Water near a pulp and paper factory had the highest levels.

LLE was used to concentrate 14 PAHs from bulk precipitation (wet and dry deposition) and surface water in Northern Greece.86 Glass funnels were attached to 1 l amber bottles to collect samples. Analysis was done by HPLC-FLD and collected samples were filtered through glass wool, extracted with HEX, and dried with anhydrous sodium sulfate. Rotary evaporation and N2 blowdown reduced the volume to 5 ml, and the residue was redissolved in ACN. The highest values obtained were for NAP, 426 ng 1" \ and the lowest for B[k]F, 1.0 ng 1" \ The £PAH14 ranged from 225 to 672 ng l"For surface waters, NAP was again the predominant PAH detected at 677 ng 1"1 and B[k]F was the lowest at 0.2 ng 1" \ The £PAH14 ranged from 184 to 627 ng 1" \ Higher concentrations were measured in winter months and concentrations in surface waters were lower than in precipitation. Bulk PAHs were measured in Paris and other sites in rural France.87 Stainless steel funnels were attached to aluminum collection tanks. LLE with HEX/DCM (85:15, v/v) was carried out after adding sulfides to sequester mercury. Rotary evaporation concentrated the samples and solvent was changed to ACN for HPLC with UV and FLD. The XPAH14 of the EPA 16 PAHs were quantified and it was also found that winter concentrations were two to three times greater than summer concentrations because of increased fossil fuel use. The six potential carcinogenic PAHs listed by the IARC accounted for 19% of the total, of which 3% was B[a]P. PHN, FLA, PYR, and CHY accounted for 62 to 71% of the total. PAH concentrations decreased proportionally from the main population center, Paris. In winter, XPAH14 for rural sites ranged from 25 to 30 ng 1"1 but in Paris the XPAH14 was 221 ng 1" In the summer months, XPAH14 for rural sites averaged 12 to 15 ng 1"1 and in Paris the XPAH14 averaged 124 ng 1" \

0 0

Post a comment