Determination of catecholamines and metanephrines in urine by capillary electrophoresis–electrospray ionization–time-of-flight mass spectrometry

A method successfully coupling capillary electrophoretic separation to time-of-flight mass spectrometric (TOFMS) detection for the simultaneous analysis of catecholamines (dopamine, norepinephrine, and epinephrine) and their O-methoxylated metabolites (3-methoxytyramine, normetanephrine, and metanephrine) is described. The inner capillary wall was coated with polyvinyl alcohol in order to obtain baseline resolution of catecholamines and metanephrines and to ensure reproducibility without extensive restorative washing of the capillary. Using electrokinetic injection, detection limits of 0.3 μM for dopamine and norepinephrine, 0.2 μM for 3-methoxytyramine and normetanephrine, and 0.1 μM for epinephrine and metanephrine were achieved with standard solutions. The usefulness of this approach was demonstrated by applying the developed method to the analysis of a spot collection of human urine from a healthy volunteer. The catecholamines and metanephrines were removed from the urine samples and preconcentrated by simultaneous SPE on cation-exchange sorbents. The recoveries of all analytes, with the exception of epinephrine (75%), were over 80%. Catecholamines and metanephrines in the urine samples were quantitated using 3,4-dihydroxybenzylamine as an internal standard. Submicromolar concentrations, consistent with the catecholamine and metanephrine levels reported for normal human urine, were detected.