Chiral pollutants pesticides

Capillary electrophoresis has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear-aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various... 

Normally, the chiral pollutants in the environment occur at low concentrations and therefore a sensitive detection method is essential and is required in chiral CE. The most commonly used detectors in the chiral CE are UV, electrochemical, fluorescence, and mass spectrometry. Mostly, the detection of the chiral resolution of drugs and pharmaceutical in CE has been achieved by a UV mode and therefore the detection of the chiral pollutants may be achieved by the same method. The selection of the UV wavelength depends on the type of buffer, chiral selector, and the nature of the environmental pollutants. The concentration and sensitivity of UV detection are restricted insofar as the capillary diameter limits the optical path length. It has been observed that some pollutants, especially organochloro pesticides, are... 

Previous sections have illustrated the complexity of most of the compound-specific analyses developed in the environmental field. It is easy then to figure out that the accurate determination of a possible enantiomeric enrichment of chiral pollutants is even more difficult owing to the many co-elution problems and low concentration levels of the analytes. This difficulty could explain the somehow limited research conducted on this topic. However, its interest is clear. Industrial contaminants, such as PCBs or toxafene, are released into the environment as racemates. Therefore, a nonracemic composition of these pollutants might be evidence of selective biotransformation and/or bioaccumulation. Some studies have also pointed to different biological and toxic behaviour for each of the enantiomers [56], something that can be especially relevant for pesticides exhibiting chiral properties. 

CE has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, and so on. Sarac, Chankvetadze, and Blaschke " resolved the enantiomers of 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid using CD as the BGE additive. The CDs used were native, neutral, and ionic in nature with phosphate buffer as BGE. Welseloh, Wolf, and Konig investigated the CE method for the separation of biphenyls, using a phosphate buffer as BGE with CD as the chiral additive. Miura et al., used CE for the chiral resolution of seven phenoxy acid herbicides using methylated CDs as the BGE additives. Furthermore, the same group resolved 2-(4-chlorophenoxy) propionic acid (MCPP), 2-(2,4-dichlorophenoxy) propionic acid (DCPP), (2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chlorophenoxy) propionic acid (2,4-CPPA), [(2,4,5-... 

Figure 2.1 The chemical structures of some chiral pollutants, (a) Aliphatic organochlorine pesticides (b) aromatic organochlorine pesticides (c) phosphorous pesticides.

Pesticides and agrochemicals are mostly used in agriculture and in forestry activities. These chiral and nonchiral xenobiotics contaminate rivers during the course of rainfall and irrigation processes. However, some chiral pesticides have been reported at the poles and, hence, found in river water which comes from melting of snow at the poles. Another possibility for the presence of chiral pollutants in river water may be the dynamic exchange of pollutants between river water and the atmosphere (near agricultural fields). In view of this, some workers have tried to detect chiral pesticides in river water. 

Chiral pollutants from various sources are contaminating our environment, as discussed above. The presence of chiral pollutants in sea water and sediment indicates the transportation of these pollutants from the point of origin (source) to the sea. There are many pesticides that have already been banned for a long time, but their presence in sea water shows their persistence in the environment These chiral pollutants, especially pesticides, have been reported in the various body parts of aquatic and terrestrial animals, including human beings, and have entered into the body through the food chain. A detailed search of the literature indicates that only a few reports on the detection of chiral pollutants are available. 

The photochemical conversion of chiral agrochemicals and xenobiotics is achiral in nature. Several studies have been carried out to determine enantioselective photochemical degradation [45, 71-73], but all of these reports have indicated the nonenantioselective decomposition of chiral pollutants. It can be concluded that the photochemical decomposition of chiral pollutants is nonenantioselective. Busser and Muller [71] and Koske et al. [72] studied the photoconversion of cyclodiene, heptachlor, cis- and tran5-chlordane and cis- and /ran -nonachlor, and the authors reported nonenantioselective conversion of these pesticides. However, Huhnerfuss et al. [45] reported variation in the enantiomeric ratios of jS-PCCH formed by enzymatic action, in the presence of light, provided that the enzymatic process is less effective. 

Besides chiral pesticides and other chiral pollutants, one of the enantiomers of certain types of drug is also toxic. Therefore, the presence of... 

In environmental science chirality has an important role as degradation of some achiral pollutants result in chiral toxic metabolites. Therefore, predicting the exact toxicities of the pollutant concentrations of both enantiomers is required and essential. For example, two enantiomers of a-hexachlorocyclo-hexane pesticide have different toxicities. Moreover, the rates of degradation of the enantiomers of a-hexachlorocyclohexane are also different [9,10]. 

Garrison, A.W. Schmitt-Kopplin, P. Avants, J.K. Analysis of the enantiomers of chiral pesticides and other pollutants in environmental samples by capillary electrophoresis. Methods Mol. Biol. 2008, 384, 157-170. 

UV detection is used in most chiral analysis by HPLC and other liquid chromatographic modalities. However, some other detectors, such as conductivity, fluorescent and refractive index types, are also used. The choice of detector depends on the properties of the racemic compound to be resolved [41, 144]. Chiroptical detectors, which are based on the principle of polarimetry [145] or circular dichroism [146, 147], are also available. The enantiomer (+)- or (—)-notation is determined by these detectors. Some organochlorine pesticides are not UV-sensitive, and hence they are difficult to detect in liquid chromatography. The detection of these types of pollutant can be achieved by using a mass spectrometry (MS) detector, and therefore LC-MS instruments are now being put on the market for routine use [148, 149]. 

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