Determination of dihydroxyphenylalanine and dihydroxyphenylacetic acid in biological samples by coupled-column liquid chromatography with dual coulometric-amperometric detection.
Adrenaline, noradrenaline, dopamine and dihydroxyphenylalanine in brain tissue and dihydroxyphenylacetic acid in plasma have been determined by direct injection of brain homogenates or plasma into a liquid chromatographic system comprising three columns, one packed with a boronic acid gel and two with reversed-phase material. The catecholamines and dihydroxyphenylalanine were selectively adsorbed on the boronic acid gel and separated by ion-pair chromatography on the reversed-phase columns. DOPAC was determined in a modified system without the addition of ion-pairing reagents. The catechols were detected by coulometry or amperometry with two working electrodes, operated in the oxidative-reductive mode. The reductive signal was used for quantification. The limits of determination were 0.05 nmol g(-1) with 40 mg brain tissue and 2 nmol 1(-1) with 0.5 ml plasma for DOPA and DOPAC respectively. The limit of quantification of DA and DOPAC in urine was about 0.1 micromol l(-1).
Edlund
P O
PO
Department of Bioanalytical Chemistry, Research and Development Laboratories, Astra Läkemedel AB, S-151 85 Södertälje, Sweden.