ENANTIOMERIC SEPARATION OF ACIDIC HERBICIDES BY CAPILLARY ELECTROPHORESIS USING VANCOMYCIN AS CHIRAL SELECTOR

In this study vancomycin has been used as chiral selector for the enan tiomeric separation of several free acid herbicides, namely aryloxypro pionic (mecoprop, fenoprop and dichlorprop), nzoyl-N-(3-chloro-4-fluor ophenyl)-2-aminopropionic acid (flamprop) and aryloxyphenoxypropionic (haloxyfop, fluazifop, diclofop and fenoxaprop). The partial filling m ethod was used in order to increase the sensitivity of the electrophor etic method; vancomycin was not present at the detector path during th e detection due to its positive charge and to the absence/reduction of the electroosmotic flow at the operating pH. The pH of the BGE, the c apillary temperature and the vancomycin concentration influenced both effective mobility and resolution of the studied compounds. The increa se of vancomycin concentration caused a general increase of migration time, resolution and selectivity, the best results have been achieved when a 6 mM concentration of chiral selector was used. Using such a co ncentration of vancomycin, baseline resolution was obtained for all th e studied enantiomers in 4.5-8.4 min. The optimized CE method has been tested for the analysis of haloxyfop free acid metabolite in a soil s ample spiked with racemic haloxyfop ethoxyethyl ester solution. The me tabolite resulted to be a mixture of R and S enantiomers where the R f orm was about 72% (peak areas ratio). The method showed good precision for both migration time and corrected peak areas with a detection lim it of 5 X 10(-7) M. (C) 1997 Elsevier Science B.V.