Determination of D- and L-Dopas in pharmaceutical preparations by high performance liquid chromatography with chiral mobile phase

The high performance liquid chromatography using chiral mobile phase containing L-phenylalanine-copper (II) complex was evaluated for purity test and stability test of L-Dopa preparations. The influences of the complex concentration and methanol content in the mobile phase on the separation of D- and L-Dopas were studied. The complex concentration had little influence on the separation, while the decrease in methanol content increased the retention time and the resolution. The detection limits obtained with UV detector and electrochemical detector were compared, and it was found that electrochemical detector could detect much less D-Dopa in the presence of L-Dopa than UV detector. D- and L-Dopas in tablets were determined simultaneously by connecting a UV detector and an electrochemical detector in series.