METHOD FOR THE DETERMINATION OF GAMMA-L-GLUTAMYL-L-DIHYDROXYPHENYLALANINE AND ITS MAJOR METABOLITES L-DIHYDROXYPHENYLALANINE, DOPAMINE AND 3,4-DIHYDROXYPHENYLACETIC ACID BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A high-performance liquid chromatographic method for the analysis of γ-l-glutamyl-l-dihydroxyphenylalanine (gludopa) and its major metabolites l-dihydroxyphenylalanine (l-DOPA), dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) is described. High sensitivity is achieved with a multi-cell coulometric detector utilising the specific electrochemical properties of gludopa (limit of detection 10 pg on-column). The retention time of gludopa was both pH-dependent and sensitive to negatively charged ion-pairing agents. An alumina-based solid-phase sample preparation technique with dihydroxybenzylamine as internal standard is described for plasma and urine (limit of detection 40 pg/ml) and an ultrafiltration technique is described for tissues (limit of detection 1-10 ng/g). After treatment with 50 mg/kg gludopa, in excess of twenty separate catecholic metabolic peaks can be detected in rat urine, whereas in humans after 9 mg/kg the only catechols detected were l-DOPA, dopamine and DOPAC. © 1990.