DETERMINATION OF 3,4-DIHYDROXYPHENYLACETIC ACID AND 5-HYDROXYINDOLEACETIC ACID IN HUMAN PLASMA BY A SIMPLE AND RAPID HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY ASSAY

In order to study the pharmacodynamic effects of drugs on dopamine and serotonin metabolism, a reversed-phase HPLC assay coupled with electr ochemical detection (ECD) for measuring plasma concentrations of 3,4-d ihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HI AA) was developed, The system was operated isocratically using a mobil e phase of aqueous 0.03 M KH2PO4 buffer containing 0.15 mM EDTA in met hanol (8.75:1.25), with a final pH of 4.0. The flow rate was set at 1. 5 mL/min, and potentials at +450 mV. Using a signal to noise ratio of >3, the minimum detection limit assessed by direct on-column injection of a standard solution for DOPAC and 5-HIAA was <1 pg. The assays wer e linear from basal concentrations (1-10 ng/mL) to 100 ng/mL. The intr a- and interassay variations were <10% and <20%, respectively.