Enantiomeric separation of naphthalene-2,3-dicarboxaldehyde derivatized dl-3,4-dihydroxyphenylalanine and optical purity analysis of l-3,4-dihydroxyphenylalanine drug by cyclodextrin-modified micellar electrokinetic chromatography

A new cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) method for the enantiomeric separation of 3,4-dihydroxyphenylalanine (DOPA), derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) to produce cyanobenzoisoindole (CBI) derivative, has been developed. The unsubstituted α-, β-, γ-cyclodextrins (CDs) and hydroxypropyl-substituted α-, β-, γ-CDs, as chiral selector, were examined for the enantiomeric separation of CBI-dl-DOPA. In addition to the concentration of chiral selector, some other experimental factors also have been optimized, such as concentration of borate buffer, content of sodium dodecyl sulphate (SDS), pH of electrolyte and applied voltage. Optimal separation was obtained at pH 8.0, 100 mM borate solution containing 5 mM HP-γ-CD and 120 mM SDS, as well as 18 kV applied voltage and 25 °C capillary temperature. Detection was followed by direct UV absorptiometric measurements at 254 nm. The developed method was employed for optical purity analysis of levodopa drug and allowed the determination of 0.14% d-DOPA in l-3,4-dihydroxyphenylalanine (levodopa) with well peak identification.