Abstract
The different activity and toxicity that the enantiomers of agrochemicals may have requires the development of stereoselective analytical methodologies enabling the individual determination of each enantiomer. The aim of this work was to develop the first Electrokinetic Chromatography methodology enabling the simultaneous enantiomeric separation of carfentrazone-ethyl herbicide and its hydrolysis metabolite carfentrazone. The use of an anionic cyclodextrin as chiral selector (captisol at 2.5% (w/v)) in a 25 mM acetate buffer, at a temperature of 30 °C, and an applied voltage (reverse polarity) of −30 kV, allowed the simultaneous separation of the four enantiomers of the two compounds studied in 6.8 min with enantiomeric resolutions of 5.0 for carfentrazone-ethyl and 5.1 for carfentrazone. Analytical characteristics of the developed method were evaluated and found adequate to achieve the quantitation of carfentrazone-ethyl and carfentrazone. Analysis of a commercial herbicide formulation showed the potential of the method for the quality control of these agrochemical products. Degradation studies for carfentrazone-ethyl revealed that no significant degradation took place in cleaned sand samples while a significant but not stereoselective degradation took place in soils for the whole period of time considered (seven days).
Highlights
30–40% of agrochemicals have at least one chiral center in their molecule [1] and are usually marketed as racemates [2]
The use of an anionic cyclodextrin as chiral selector (captisol at 2.5% (w/v)) in a 25 mM acetate buffer, at a temperature of 30 ◦C, and an applied voltage of −30 kV, allowed the simultaneous separation of the four enantiomers of the two compounds studied in 6.8 min with enantiomeric resolutions of 5.0 for carfentrazone-ethyl and 5.1 for carfentrazone
Electrokinetic Chromatography enabled the simultaneous enantiomeric separation of carfentrazone-ethyl herbicide and its hydrolysis metabolite carfentrazone using an anionic cyclodextrin as chiral selector
Summary
30–40% of agrochemicals have at least one chiral center in their molecule [1] and are usually marketed as racemates [2] Their enantiomers may have a different activity or environmental behavior so chiral analytical methodologies are required in order to achieve the quality control of commercial agrochemical formulations or the analysis of environmental samples. Carfentrazone-ethyl (ethyl-(R,S)-2-chloro-3-(2-chloro-5-(4-difluoromethyl-4,5-dihydro3-methyl-5-oxo-1H-1,2,4-triazol-1-yl)-4-fluorophenyl) propionate) is a chiral postemergence triazole herbicide used against broadleaf weeds in wheat, corn, and soybeans [4] It is commercialized as a racemic mixture Duan et al demonstrated that the S-enantiomer presented double herbicidal activity and 4.8 times more toxicity towards aquatic organisms than (R)-carfentrazone-ethyl [5]. This metabolite exhibits herbicidal activity but, unlike carfentrazoneethyl, there is differential tolerance between species due to its breakdown into unknown metabolites [7]
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