Determination of cabergoline and l-dopa in human plasma using liquid chromatography–tandem mass spectrometry

We determined cabergoline and l-dopa in human plasma using liquid chromatography–mass spectrometry with tandem mass spectrometry (LC–MS–MS). The deproteinized plasma samples with organic solvent or acid were analyzed directly by reversed-phase liquid chromatography. Using multiple reaction monitoring (MRM, product ions m/z 381 of m/z 452 for cabergoline and m/z 152 of m/z 198 for l-dopa) on LC–MS–MS with electrospray ionization (ESI), cabergoline and l-dopa in human plasma were determined. Calibration curves of the method showed a good linearity in the range 5–250 pg/ml for cabergoline and 1–200 ng/ml for l-dopa, respectively. The limit of determination was estimated to be approximately 2 pg/ml for cabergoline and approximately 0.1 ng/ml for l-dopa, respectively. The method was applied to the analysis of cabergoline and l-dopa in plasma samples from patients treated with these drugs. The precision of analysis showed coefficients of variation ranging from 3.8% to 10.5% at cabergoline concentration of 13.8–26.2 pg/ml and from 2.9% to 8.9% at an l-dopa concentration of 302.5–522.1 ng/ml in patient plasma. As a result, the procedure proved to be very suitable for routine analysis.