Simultaneous quantitation of catecholamines and O-methylated metabolites in urine by isocratic ion-pairing high-performance liquid chromatography with amperometric detection.

A simple high-performance liquid chromatographic procedure was developed for the simultaneous determination of catecholamines and metanephrines in urine. One-step sample preparation was achieved with Bio-Rex 70 ion-exchange resin. The extract was assayed on a C18 reversed-phase column. Dihydroxybenzylamine was used as an internal standard. The eluent was monitored by an electrochemical detector with an oxidation potential of +0.85 V. The use of 1-heptanesulphonic acid in the mobile phase permitted the separation of norepinephrine, epinephrine, dopamine, normetanephrine and metanephrine in a single chromatogram. The corresponding detection limits were 5, 9, 14, 10 and 30 nmol/l, respectively. For the between-day precision, the coefficients of variation at physiological and pathological concentrations were less than 11%. Compounds with similar chemical structures and drugs commonly prescribed for the treatment of hypertension were assayed and found not to cause interferences in the chromatogram. The assay is reliable and is suitable for the analysis of clinical specimens. Reference values were established for normotensive Chinese patients with no neurological or endocrine disorders and also for patients suffering from essential hypertension.