Simultaneous kinetic determination of epinephrine and norepinephrine by the stopped-flow technique.

A stopped-flow method for the simultaneous determination of epinephrine and norepinephrine, two catecholamines with a wide spectrum of biological activity, is proposed. The method is based on the oxidation of these compounds with 1,10-phenanthroline-iron(III) complex, which is monitored by measuring the initial rate of change of the absorbance of the ferroin formed at 510 nm. The difference in kinetic behaviour between the two species was exploited by applying a modified version of the proportional-equation method for the resolution of epinephrine-norepinephrine mixtures at the micrograms ml-1 level over the ratio range 1:10-10:1, with an error of less than 5% and an average precision of about 2.5%. The method was successfully applied to the determination of the two catecholamines in pharmaceuticals.