Simultaneous determination of free catecholamines and epinine and estimation of total epinine and dopamine in plasma and urine by high-performance liquid chromatography with fluorimetric detection.

Epinine (N-methyldopamine) is the pharmacologically active hydrolysis product of the prodrug ibopamine, which is currently being widely studied for the treatment of congestive heart failure. This paper reports a sensitive and reliable method for the simultaneous determination of free catecholamines and epinine in plasma and urine. The compounds are isolated from plasma or urine by a specific liquid-liquid extraction, derivatized with the selective fluorogenic agent 1,2-diphenylethylenediamine, and quantitated by high-performance liquid chromatography with gradient elution and fluorimetric detection. The limits of detection for the derivatized catecholamines and epinine are 0.3-0.6 pg of injected compound. Intra- and inter-assay coefficients of variation of all four compounds are good (1-8%), as are the accuracy and linearity. A method is also reported for the determination of total dopamine and epinine in plasma and urine based on the same principle. This method, in which deconjugation is accomplished by acid hydrolysis at 95 degrees C, also shows good sensitivity and reproducibility.