Adsorptive Behavior of Catechol Violet and Its Thorium Complex on Mercury Electrode in Aqueous Media

Abstract

Cyclic voltammetry and chronocoulometry have been used for characterization of catechol violet (CV) atthe hanging mercury drop electrode in acetic acid-sodium acetate bufer solution. At pH 2.94 a nearly symmetriccyclic voltammetric wave due to an irreversible weak adsorption of CV on mercury was obtained at concentrationof 0.53mmol dm-3. Under these conditions, CV adsorbes in a monolayer. Upon increasing the concentration, the sym-metry of the wave decreases; it can be attributed to a mixed difusion adsorption process. The amount of the adsorbedcatechol violet on the HMDE expressed as surface concentration as well as the surface areas ocupied by one molecule(s) were calculated. It was found that the values obtained for G and s utilizing cyclic voltammetric and chrono-coulometry are almost identical. A 1:1 and 1:2 Th (IV)-CV complexes are formed on addition of thorium (IV)to catechol violet. These complexes are adsorbed and reduced on the HMDE at more negative potentials than thepeak potential of free CV. Using the square-wave (SW) technique, the adsorptive cathodic stripping voltammetry,ACSV, of these complexes was studied. It was found that the SW-ACSV of Th(IV)-CV can be applied to thedetermination of thorium at the nanomole level. Optimum conditions and the analytical method of determination werepresented and discussed.