Analyses of chiral pesticides

The need to develop and use chiral chromatographic techniques to resolve racemates in pesticide residues will be driven by new hazard and risk assessments undertaken using data from differential metabolism studies. The molecular structures of many pesticides incorporate chiral centers and, in some cases, the activity differs between enantiomers. Consequently, in recent years manufacturers have introduced resolved enantiomers to provide pesticides of higher activity per unit mass applied. For example, the fungicide metalaxyl is a racemic mix of R- and 5-enantiomers, both having the same mode of action but differing considerably in effectiveness. The -enantiomer is the most effective and is marketed as a separate product metalaxyl-M. In future, it will not be satisfactory to rely on hazard/risk assessments based on data from metabolism studies of racemic mixes. The metabolism studies will need to be undertaken on one, or more, of the resolved enantiomers. 

Harris, and A.G. Warburton, in Principles and Practices of Method Validation, ed. A. Fajgeli and A. Ambms, RSC Special Publication No. 256, Royal Society of Chemistry, Cambridge (2000). 

Fussell, K. Jackson-Addie, S.L. Reynolds, and M. Wilson, J. Agric. Food Chem., 50, 441 (2002). 

in Emerging Strategies for Pesticide Analysis, ed. T. Cairns and J. Sherma, CRC Press, Boca Raton, FL, Chapt. 9, p. 217 (1992). 

AOAC Methods PAM211 and PAM 231, Association of Official Analytical Chemists, Arlington, VA (1984). 

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