title: Quantitative determination of free and total dopamine in human plasma by LC-MS/MS: the importance of sample preparation.
abstract: BACKGROUND
  Two methods have been developed and validated for the determination of free and total dopamine in human plasma. They are based on solid-phase extraction of the analyte from the matrix by covalent complexation with phenylboronic acid, followed by derivatization with ethylchloroformate. The derivative is quantified by reversed-phase liquid chromatography on a C18 column and positive electrospray ionization MS/MS.
  
  
  RESULTS
  The high selectivity obtained, in combination with the stable and relatively non-polar nature of the derivatized analyte, enables the reliable quantification of dopamine in the range 0.05 to 20 ng/ml in a 5 min run time, using only 100 µl of sample. Total dopamine concentrations are determined (range 1 to 400 ng/ml) by including an acidic hydrolysis step, which converts the sulphate and glucuronide conjugates to free dopamine prior to extraction. The method was applied to quantify free and total dopamine levels in human plasma after dosing with the anti-Parkinson's drug combination L-dopa/carbidopa with and without entacapone.
  
  
  CONCLUSIONS
  A sensitive and selective LC-MS/MS method has been developed and validated for the determination of free and total dopamine in human plasma. This article demonstrates how essential careful optimization of the sample preparation procedures was for developing a successful method.
authors: Bioanalytical Laboratory, PRA International, Westerbrink 3, 9405 BJ Assen, The Netherlands. merbelnicovande@praintl.com
authors: Nico C
authors: NC
authors: van de Merbel
authors: Gert
authors: G
authors: Hendriks
authors: Roos
authors: R
authors: Imbos
authors: Johanna
authors: J
authors: Tuunainen
authors: Juha
authors: J
authors: Rouru
authors: Hanna
authors: H
authors: Nikkanen
mesh_terms: D000818:Animals; D002853:Chromatography, Liquid / Q000295:instrumentation / Q000379:methods*; D004298:Dopamine / Q000032:analysis* / Q000097:blood* / Q000737:chemistry; D005563:Formic Acid Esters / Q000737:chemistry; D006801:Humans; D015394:Molecular Structure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D052616:Solid Phase Extraction / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000295:instrumentation / Q000379:methods*
chemical_list: D005563:Formic Acid Esters; C007658:ethyl chloroformate; D004298:Dopamine