Determination of catecholamines in urine (and plasma) by liquid chromatography after on-line sample pretreatment on small alumina or dihydroxyborylsilica columns.

The possibilities of the on-line pre-concentration of catecholamines on small columns packed with aluminium oxide (10 micron) or dihydroxyborylsilica (5 micron) prior to high-performance liquid chromatography (HPLC) were investigated. For both pre-concentration materials the influence of the pH of the mobile phase on the retention characteristics was studied for the catecholamines and some of their derivatives lacking the catechol and/or the amine function. The recovery of the catecholamines and the loading capacity on some pre-columns was then investigated. The compatibility of the pre-concentration system with several HPLC systems, viz., reversed-phase ion-pair, ion-exchange and reversed-phase ion-pair partition chromatography, was studied. Combined with amperometric or fluorimetric detection, the method was applied to the determination of free catecholamines in urine, using dihydroxybenzylamine or epinine as internal standards. An example of the determination of catecholamines in plasma containing 100 pg/ml of each catecholamine is also shown.