Enantioseparation of 3,4-dihydroxyphenylalanine and 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid by capillary electrophoresis using cyclodextrins

The enantiomeric separations of 3,4-dihydroxyphenylalanine (dopa) and 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid (carbidopa) by capillary electrophoresis were studied using several native, neutral and anionic cyclodextrins as chiral additives and uncoated fused-silica capillaries. The effect of the type and concentration of the cyclodextrin added to 20 mM phosphate buffer (pH 2.5) on enantioseparation and migration times was studied. A high resolution value of 15.63 was obtained for dopa enantiomers with a buffer containing 20 mM single isomer, heptakis(2,3-diacetyl-6-sulfato)-β-cyclodextrin. The enantiomers of carbidopa were separated using 20 mM carboxymethyl-β-cyclodextrin as a chiral resolving agent. Both methods allowed the determination of 0.1% of the d-enantiomer (second migrating) in the presence of the l-enantiomer (first migrating) of dopa and carbidopa with a good precision. These methods also gave good results in terms of precision for both peak area, migration time, linearity and accuracy.