Automated analysis of homovanillic acid and 5-hydroxyindole-3-acetic acid in biological fluids by coupled-column liquid chromatography and dual coulometric-amperometric detection.

Homovanillic acid (HVA) and 5-hydroxyindole-3-acetic acid (5-HIAA) were determined by direct injection of plasma, urine and cerebrospinal fluid (CSF) into a liquid chromatographic system comprising three columns, one packed with an anion-exchange gel and two with reversed-phase material. The acidic compounds were isolated by anion-exchange on the first column, enriched on the second and separated by reversed-phase chromatography on the last column. 5-HIAA and HVA were detected by coulometry and amperometry on two working electrodes coupled in series, giving limits of determination in plasma of 4 and 5 nmol l(-1) respectively. Endogenous plasma, urine and CSF-levels were determined with a precision (RSD) of 2-4%. 3-Methoxy-4-hydroxyphenylpropionic acid was identified in normal plasma and urine.