Valence discriminative detection of metal cations by a chromotropic acid-grafted glassy carbon electrode

Covalent grafting of chromotropic acid (CA) moiety to a glassy carbon electrode was performed by electrochemical reduction of the corresponding diazonium cation generated in situ. Grafted electrodes were subjected to the electrochemical detection of multivalent cations using Fe(CN)(6)(3-/4-) as an electrochemical probe molecule. In the absence of metal cations, redox reaction of the anionic probe was depressed by electrostatic repulsion between the probe and negatively charged CA moieties on the electrode surface. Binding of tetravalent cations such as Zr(IV) and Hf(IV) and trivalent cations such as Al(III) and lanthanide(III) to the CA moiety on the electrode surface resulted in an increase in the current intensity of the probe due to a decrease in electrostatic repulsion. Highly selective detection of the tetravalent cations was achieved in the micromolar concentration range at pH 1.0.