Study of the electrooxidative behaviour of 5-hydroxyindole-3-acetic acid, 5-hydroxytryptophan and serotonine in the presence of sodium ethylenediaminetetraacetic acid

Abstract

The great instability of the indole derivatives 5-hydroxytryptophan (5-HTP), serotonine (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) in strong acid medium and the protective role of sodium ethylenediaminetetracetate (EDTA H 2Na 2) could be explained by their electrooxidative behaviour on a carbon paste electrode. Voltamperometric curves obtained in a 1–8 pH range show that oxidation occurs in two irreversible steps; the mechanism is more complex than a simple electron transfer. For the three molecules, new redox couples have been detected on cyclic voltammograms at lower potentials than the parent compound, indicating that more easily oxidized derivatives are formed. On the other hand, the anodic oxidation of EDTA H 2Na 2 has been investigated and in the present case the molecule is not acting by complexing metal traces but should actually be considered a competitive agent preventing the second oxidation step of the indole derivatives.