Simultaneous Determination of 3,4‐Dihydroxyphenylalanine, 5‐Hydroxytryptophan, Dopamine, 4‐Hydroxy‐3‐Methoxyphenylalanine, Norepinephrine, 3,4‐Dihydroxyphenylacetic Acid, Homovanillic Acid, Serotonin, and 5‐Hydroxyindoleacetic Acid in Rat Cerebrospinal Fluid and Brain by High‐Performance Liquid Chro

Abstract: A method using reversed‐phase ion‐pair high‐performance liquid chromatography with electrochemical detection for the simultaneous determination of tryptophan (TRP), 3,4‐dihydroxyphenylalanine (DOPA), and their metabolites in whole brain, small‐brain parts, and cerebrospinal fluid of rats has been developed. The sample preparation requires only homogenization in perchloric acid and centrifugation before injection onto the column. With a LiChrosorb RP‐18 (10 μm) column and a mobile phase consisting of a phosphate (NaH2PO4, 0.1 M)‐methanol mixture with octylsulfonate (2.6 × 10−3M) at pH 3.35 and 26°C, the separation of DOPA, dopamine, norepinephrine, 3,4‐dihydroxyphenylacetic acid, homovanillic acid, 4‐hydroxy‐3‐methoxyphenylalanine, TRP, 5‐hydroxytryptophan (SHTP), serotonin, and 5‐hydroxyindole‐acetic acid was achieved. The method has been applied to study the effect of α‐monofluoromethyldopa alone and in combination with L‐DOPA or L‐5‐HTP, on the catechol and 5‐OH indole levels in brain and CSF of the rat.