SEPARATION OF PHENOXY ACID HERBICIDES AND THEIR ENANTIOMERS BY HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS

Capillary electrophoresis conditions in the free solution mode (capill ary zone electrophoresis) were established for the separation and dete ction of 2,4-dichlorophenoxyacetic acid and three optically active phe noxy acid herbicides (dichlorprop, mecoprop and fenoprop). A 50 mM ace tate buffer at pH 4.5 gave the best separation, using a 50 cm (to dete ctor) x 75 mu m I.D. fused-silica column; the column temperature was 3 0 degrees C, separation voltage 20 kV and optimum detector wavelength 230 nm. Separation of the four herbicides required less than 15 min un der these conditions. Baseline separation of the two enantiomers of ea ch of the three optically active herbicides, separately and in mixture s of the three, was accomplished by the addition of 25 mM tri-O-methyl -beta-cyclodextrin to the acetate separation buffer. Di-O-methyl-beta- cyclodextrin or alpha-cyclodextrin (CD) separated enantiomers of dichl orprop and mecoprop, but not those of fenoprop; beta-CD provided very little separation and gamma-CD gave no separation. Addition of methano l to the separation buffer increased separation, but doubled migration times. Over a variety of sample concentrations and injection times, r eproducibilities of migration times of racemates and enantiomers range d 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.