Polarity polychlorinated biphenyls

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Picer and Picer [357] evaluated the application ofXAD-2, XAD-4, and Tenax macroreticular resins for concentrations of chlorinated insecticides and polychlorinated biphenyls in seawater prior to analysis by electron capture gas chromatography. The solvents that were used eluted not only the chlorinated hydrocarbons of interest but also other electron capture sensitive materials, so that eluates had to be purified. The eluates from the Tenax column were combined and the non-polar phase was separated from the polar phase in a glass separating funnel. Then the polar phase was extracted twice with n-pentane. The -pentane extract was dried over anhydrous sodium sulfate, concentrated to 1 ml and cleaned on an alumina column using a modification of the method described by Holden and Marsden. The eluates were placed on a silica gel column for the separation of PCBs from DDT, its metabolites, and dieldrin using a procedure described by Snyder and Reinert [359] and Picer and Abel [360]. 

Fig. 3 Scientific studies in water. Ph pharmaceuticals Ft phthalates Fu fungicides HA acidic herbicides HCB hexachlorobenzene PCBs polychlorinated biphenyls OCs organochlorine pesticides PPs polar pesticides...

The ubiquity of PCBs is indicated by their presence in environmental samples from the polar regions of air, snow, ice, water, and in living organisms (Norstrom et al. 1988 Hargrave et al. 1989 Larsson et al. 1992 Tanabe et al. 1993). The presence of PCBs in such remote areas suggests the importance of atmospheric transport. The Committee on the Assessment of Polychlorinated Biphenyls... 

The formation of polar metabolites from nonpolar materials may actually facilitate monitoring programs—in many cases the polar chemicals are highly concentrated in certain body fluids such as bile and urine. On the other hand, materials such as certain cyclodienes and polychlorinated biphenyls, which are very lipid soluble and resistant to metabolism, may accumulate and these chemicals may persist in the environment and may be transferred via the food chain to man. There is also interest in these biotransformation processes in lower organisms since the simplicity of these systems may lead to a better understanding of the phylogenetic development of xenobiotic metabolism. 

At supercritical conditions these solvents effectively extract relatively polar compounds such as polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans without the use of a cosolvent (Roth, 1996). 

Supercritical C02 has also been tested as a solvent for the removal of organic contaminants from soil. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlorinated biphenyls (PCBs), may be removed from soil samples (77). Supercritical C02 can also extract from soil the following hydrocarbons, polyaromatic hydrocarbons, chlorinated hydrocarbons, phenols, chlorinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

Liquid-liquid extraction and sorbent accumulation are the most commonly employed isolation-concentration methodologies. In their ideal forms, these methods readily extract or accumulate relatively hydrophobic compounds such as polynuclear aromatic hydrocarbons (PAHs) or polychlorinated biphenyls. However, when HPLC is likely to be the method of choice, the compounds are likely to be highly polar or ionic. In these common cases, adaptation of the traditional methodology can readily serve to carry out the necessary isolation. 

Used for polar compounds such as alcohols, glycols, ketones, aldehydes has also been used for polychlorinated biphenyls and phthalates more data are provided in the Adsorbents for Gas Chromatography table... 

Fat, for non-polar compounds (e.g., organochlo-ride pesticides as DDT and polychlorinated biphenyls)... 

The mixture of polar and nonpolar solvents often employed for extraction of polycyclic aromatic hydrocarbons (PAHs) or polychlorinated biphenyls (PCBs) is a hexane and acetone combination. Ethyl acetate and cyclohexane are used for extraction of chlorinated organic compounds [46]. 

Kumar, K.S., Karman, K., Corsolini, S., Evans, T., Giesy, J.P., Nakanishi, J., Masunaga, S. (2002). Polychlorinated dihenzo-p-dioxins, dihenzoturans and polychlorinated biphenyls in polar hear, penguin and south polar squa. Environ. Pollut. 119 115-61. 

Bioconcentration in the marine food chain can lead to animals such as seals, beluga whales, seabirds, and polar bears having concentrations of to-xaphene 10 million times higher than levels in the surrounding water. For polychlorinated biphenyls (PCBs), the amplification is 1000 million times. 

The first considerations in determining the most appropriate SPE methodology are the structure and polarity of the analytes of interest. Table 7.1 shows a selection of environmentally important compounds as examples for SPE methods development from aqueous solution. The polarity range of environmentally important analytes is broad and stretches from nonpolar compounds, such as polychlorinated biphenyls (PCBs), dioxin, and l,l,l-trichloro-2-2-bis(4-chlorophenyl)ethane (DDT), to moderately nonpolar compounds, such as polynuclear aromatic hydrocarbons (PAHs), to polar compounds such as the herbicides. The most polar compounds are those containing multiple polar functional groups or an ionic functional group, either anionic or cationic. The type of SPE cartridge and elution solvent that are used depends on the polarity of the compound. 

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