Determination of L-3, 4-Dihydroxyphenylalanine in Plasma and Urine by High-Performance Liquid Chromatography with Fluorescence Detection

Abstract

A simple and highly sensitive method for the determination of L-3, 4-dihydroxyphenylalanine (L-DOPA) in human plasma and urine is described which employs high-performance liquid chromatography with fluorescence detection. After cation-exchange chromatography on a Toyo-pak IC-SP S cartridge, L-DOPA and α-methyldopa (an internal standard) in 300μl of plasma or 10 μl of urine are converted into the corresponding fluorescent compounds by reaction with 1, 2-diphenylethylenediamine. These compounds are separated by reversed-phase chromatography on a TSK gel ODS-120T column with isocratic elution. The detection limit for L-DOPA is 10 fmol in a 100-μl injection volume.