Chiral and non chiral determination of Dopa by capillary electrophoresis.

The suitability of capillary electrophoresis for determining the enantiomeric purity of levodopa in a pharmaceutical formulation also containing benserazide was assessed. To this end, the pharmaceutical components were separated in a non-chiral medium that allowed the total amount of Dopa and that of benserazide to be quantified. The addition of a chiral crown ether to the background electrolyte allows to separate the enantiomers of this compounds. Optimizing the variables influencing the enantioresolution of Dopa affords a resolution high enough resolution to determine the amount of dextrodopa (the distomer) contained in levodopa (the eutomer) in a pharmaceutical. A relative limit of detection (RLD) is proposed as a measure of the lowest detectable enantiomeric impurity. The RLD for the determination of dextrodopa contained in levodopa was 0.1% and found to depend on the enantiomer migration order. The enantiomeric purity of levodopa in the pharmaceutical preparation and dextrodopa from Sigma was 99.5 and 99.95%, respectively.