Determination of _L-threo-3, 4-Dihydroxyphenylserine and _L-α-Methyldopa in Rat Serum by High Performance Liquid Chromatography with Fluorescence Detection

Abstract

A highly sensitive method for the determination of _L-threo-3, 4-dihydroxyphenylserine (_L-DOPS) and _L-α-methyldopa in rat serum is described. The method uses high performance liquid chromatography with fluorescence detection. L-DOPS and L-α-methy dopy (analyte and internal standard, respectively, andvice versa) in serum, after cleanup with a cation exchanger cartridge (Toyopak IC-SP S), are converted into the corresponding fluorescent compounds by reaction withmeso-1, 2-diphenylethylenediamine. The derivatives are separated by reversed phase chromatography on a TSK gel ODS-120T column. The detection limits (S/N=3) for L-DOPS and L-α-methyldopa are 6 and 9fmol for an injection volume of 100μl.