DETERMINATION OF CATECHOLAMINES IN URINE BY MICELLAR LIQUID-CHROMATOGRAPHY WITH COULOMETRIC DETECTION

The determination of catecholamines by HPLC with a sodium dodecyl-sulp hate (SDS), micellar mobile phase on a C-18 column and with coulometri c detection was studied. The eluate was conditioned at +0.25 and +0.00 V, and the current at -0.16 V was recorded. A previously developed mo del which describes the chromatographic behaviour of solutes in HPLC w ith hybrid, micellar moblie phases was used to optimize the SDS and et hanol concentrations. A mobile phase of 0.15M SDS in a phosphate buffe r of pH 3.4 and without ethanol is recommended. The limits of detectio n were 0.4-0.7 ng ml(-1). The procedure was applied to the determinati on of unconjugated L-dopa, norepinephrine and dopamine in urine. Direc t injection of the urine samples gave high results but the unconjugate d catecholamines could be determined with a single solid-phase extract ion step on an alumina column.