Several instrumental techniques of electrochemical detection have been applied in detectors for HPLC. Flow cells but also electronics have been subject to this process of development. Several authors describe successful experiences in evaluating amperometric and coulometric [1, 2] single electrode detectors. Flow cells based on different principles have been used, e. g. thinlayer [3-7], wall jet [8] and tubular cells [9, 10]. Blank constructed the basic dual amperometric detector [7], Kissinger et al. designed detectors for thin-layer dual electrode detection [11]. The same improvements are realized with the coulometric detector, the ESA 5100A Coulochem dual electrode, we use for our analytical investigations. The fundamental principle of the coulometric measuring technique is especially attractive because of its selectivity, high sensitivity and its conversion efficiency of 100%. Amperometrics detectors often react with an efficiency comprise between 1 and 10 %. The use of a low flow-through cell configuration (Fig. 1) makes possible to achieve a complete material conversion at the electrode surface providing a high coulometric yield. The results (signal response) are up to 15 times higher than in an amperometric system. In the past, in our lab, amperometric detection has been successfully used for the determination of urinary catecholamines as NE and E. Dopamine, another compound of interest which follows the same clean-up steps procedure, always appears on the catechol chromatogram, higher than the normal urinary value, this normal value being established by fluorimetry. The pH of the mobile phase, electrolyte concentration, the type o f column and the chemical procedure were modified in order to improve the separation of an possibly interfering substance which could be isographic with dopamine, but no significant results were obtained. Thanks to advances in analytical electrochemistry, dual electrode systems provide us with the chromatographic tool to solve this practical problem. As dopamine (E and NE) can be oxidized and reduced, this reversibility (redox mode) has been employed to confirm the identity of the compound in a urine extract.