ADSORPTION AND ASSOCIATION OF XANTHINE IN ABSENCE AND PRESENCE OF SOME DIVALENT METAL-IONS AT THE MERCURY SOLUTION INTERFACE/

The adsorption and interfacial orientations of xanthine were studied b y out-of-phase ac voltammetry at a hanging mercury drop electrode. The adsorption equilibrium and its attainment have been investigated as a function of various parameters such as pH, adsorption potential, temp erature, adsorption time, the nature of anions of the supporting elect rolyte and the bulk concentration of xanthine. The changes in the stac king interactions of xanthine molecules in the presence of Cd(II), Cu( II), Co(II), Ni(II); Ca(II) and Mg(II) were studied by ac voltammetry as changes in ''pits'' or ''wells'' on double layer capacitance curves due to adsorption and association of M(II)-xanthine complexes on the charged interface. The results indicate that the complexation of xanth ine molecules enhances the stacking interactions and hence would be ex pected to facilitate the formation of perpendicularly stacked layer of M(II)-xanthine complex on the electrode surface. The time dependence of the electrode impedance indicates that the formation of a compact f ilm in absence and presence of these metal ions controlled by a fixed number of nuclei and the data were analysed according to the Avrami eq uation. The adsorption parameters of xanthine have been computed at di fferent pH values in the absence and the increased presence of metal i ons. Copyright (C) 1996 Elsevier Science Ltd