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 electrochemical detection (ECD) for measuring plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hy-droxyindoleacetic acid (5-HIAA) was developed. The system was operated isocratically using a mobile phase of aqueous 0.03MKH2PO4 buffer containing 0.15mM EDTA in methanol (8.75:1.25), with a final pH of 4.0. The flow rate was set at 1.5mL/min, and potentials at +450mV. 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