Separation of phenoxy acid herbicides and their enantiomers by high-performance capillary electrophoresis

Abstract Capillary electrophoresis conditions in the free solution mode (capillary zone electrophoresis) were established for the separation and detection of 2,4-dichlorophenoxyacetic acid and three optically active phenoxy acid herbicides (dichlorprop, mecoprop and fenoprop). A 50 mM acetate buffer at pH 4.5 gave the best separation, using a 50 cm (to detector) × 75 μm I.D. fused-silica column; the column temperature was 30°C. separation voltage 20 kV and optimum detector wavelength 230 nm. Separation of the four herbicides required less than 15 min under these conditions. Baseline separation of the two enantiomers of each of the three optically active herbicides, separately and in mixtures of the three, was accomplished by the addition of 25 mM tri-O-methyl-β-cyclodextrin to the acetate separation buffer. Di-O-methyl- β-cyclodextrin or α-cyclodextrin (CD) separated enantiomers of dichlorprop and mecoprop, but not those of fenoprop; β-CD provided very little separation and γ-CD gave no separation. Addition of methanol to the separation buffer increased separation, but doubled migration times. Over a variety of sample concentrations and injection times, reproducibilities of migration times of racemates and enantiomers ranged from 1.3 to 4.6% R.S.D.; peak area and peak height reproducibilities ranged from 1.6 to 17.9% R.S.D.