SIMULTANEOUS MEASUREMENT OF L-DOPA, ITS METABOLITES AND CARBIDOPA IN PLASMA OF PARKINSONIAN-PATIENTS BY IMPROVED SAMPLE PRETREATMENT AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION

A procedure is described for the determination of l-3,4-dihydroxyphenylalanine (l-DOPA), its metabolites and carbidopa (CD) in plasma of Parkinsonian patients by high-performance liquid chromatography with dual working-electrode coulometric electrochemical detection. An efficient sample preparation scheme is presented for the isolation of l-DOPA, its metabolites and the catecholamines from the same plasma aliquot. After a simple deproteinization with methanol containing 2% of 0.5 M perchloric acid and evaporation of the solvent, l-DOPA, its metabolites and CD were separated with a 5-μm Nucleosil C18 column. Catecholamines were extracted from the supernatant of the deproteinized plasma by ion exchange on small columns and adsorption on alumina. Recoveries were close to 100 for l-DOPA, its metabolites and CD and 70 for catecholamines. The use of the same mobile phase for the concurrent assay of l-DOPA, its metabolites and catecholamines considerably increased the throughtput of samples iin the chromatographic system. The dual-electrode coulometric detector afforded peak identification by comparing current ratios. Monitoring of data from patients under l-DOPA therapy is reported. © 1990.