Simultaneous determination of levodopa and 3-O-methyldopa in human plasma by liquid chromatography with electrochemical detection.
A simple and rapid assay is described for the simultaneous analysis of levodopa (l-DOPA) and 3-O-methyldopa (3-OMD) in human plasma samples, applying an ion-pair reversed-phase liquid chromatographic method with electrochemical detection, designed for clinical trials performed to study the effect of peripheral catechol-O-methyltransferase inhibitors on the metabolism of l-DOPA. After protein precipitation of 100 microl plasma sample aliquots with perchloric acid, the analytes are directly injected, separated within 10 min and simultaneously quantified down to 20 ng/ml by an electrochemical detector equipped with a dual-electrode system operating in redox mode eliminating effectively potential endogenous and exogenous interferences. The intra-assay precision for l-DOPA and 3-OMD was 1.34-6.54 and 3.90-5.50%, whereas the inter-assay precision was 2.09-7.69 and 4.16-9.90%, respectively. The recoveries were close to 90% for l-DOPA and almost 100% for 3-OMD. Satisfactory storage stability was achieved for up to 16 weeks at -70 degrees C by stabilizing plasma samples with antioxidants.
Saxer
Christoph
C
Tsukuba Research Institute, Novartis Pharma K.K., Ohkubo 8, Tsukuba-shi, Ibaraki-ken 300-2611, Japan. christoph.saxer@pharm.novartis.com
Niina
Miyuki
M
Nakashima
Akinori
A
Nagae
Yusuke
Y
Masuda
Naoki
N
D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D004563:Electrochemistry / Q000379:methods*; D006801:Humans; D007980:Levodopa / Q000097:blood*; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000097:blood*
D014443:Tyrosine; D007980:Levodopa; C008404:3-methoxytyrosine