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-micron 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 throughput of samples in 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.
Istituto Superiore di Sanità, Rome, Italy.
C
C
Lucarelli
P
P
Betto
G
G
Ricciarello
M
M
Giambenedetti
C
C
Corradini
F
F
Stocchi
F
F
Belliardo
D002230:Carbidopa / Q000097:blood*; D002395:Catecholamines / Q000097:blood; D002396:Catechols / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D004563:Electrochemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007980:Levodopa / Q000097:blood*; D010300:Parkinson Disease / Q000097:blood*
D002395:Catecholamines; D002396:Catechols; D007202:Indicators and Reagents; D007980:Levodopa; D002230:Carbidopa