Routine analysis of catecholamines and metabolites in urine by a liquid chromatographic column switching system

A reversed-phase liquid chromatographic technique including a column switching system has been adapted for the routine measurement of catecholamines and their metabolites (14 compounds) in urine. From 1 ml of urine all the compounds and the internal standards were obtained according to combined extraction procedures involving organic solvent, anionic and weakly cationic resins. Finally four extracts (catecholamines, methoxamines, acidic and neutral derivatives) had to be chromatographed throughout a wholly automated apparatus. For each run, the column switching system determined the analytical columns to be used to obtain the separation of the compounds from interferences due to other co-extracted endogenous substances, while the analysis times remained between 20 and 40 min. Such a system allowed the rapid clean-up of columns (in direct- and back-flush mode) carried out between two consecutive injections. By coupling on-line fluorimetric and electrochemical detections the specificity of the technique could be checked, since the ratio of the responses of both detectors was an index of the purity of the peaks. Finally the advanced automation of the equipment allowed weekly the evaluation of catecholamines and the whole range of their known metabolites in 36 urine samples.