Chiral pollutants enantiomeric ratios

Zipper C., SuterM. J.-F., Haderlein S. B., Gruhl M., and Kohler H.-P. E. (1998) Changes in the enantiomeric ratio of (R) to (S) mecoprop indicate in situ biodegradation of this chiral herbicide in a polluted aquifer. Environ. Sci. Technol. 32, 2070-2076. 

Table 3.2 The enantiomeric ratios of some chiral pollutants in various ecosystem components...

Chiral pollutant Ecosystem component Enantiomeric ratio References... 

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 the chiral resolution of pollutants, GC determination of enantiomeric ratios (ERs) can be used for the quantification of the enantiomers in complex matrices, with a known quantity of the pure enantiomer added as an internal standard. With a method of enantiomer labelling, a known quantity of an enantiopure standard is added to the mixture (or an aliquot of it) and the amount of the enantiomer originally present is calculated from the change in the ER after addition of the standard. This method provides precise knowledge of the ERs of the sample and the standards [87]. In addition, the absolute configurations of the pollutants may be determined directly, and free of chiroptical evidence, by GC via co-injection of reference pollutants with known stereochemistry [87]. 

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