Diclofenac electrooxidation at nickel hydroxide and its analytical application

The voltammetric behavior in alkaline solution of a nickel‐based chemically modified electrode (Ni‐CME) prepared by oxidative electropolymerization of a nickel–tetraazaannulene complex (NiIIL) was investigated. After electrochemical deposition of the (NiIIL)n film in dichloromethane on a conducting substrate, the modified electrode was continuously cycled in alkaline solution until a steady voltammetric profile was obtained. Although upon electrochemical treatment in basic solutions the nickel–nitrogen tetracoordination of the (NiIIL)n film is probably lost, the nickel species remain entrapped inside the polymeric skeleton and exhibit stable redox behavior resembling that of the nickel hydroxide electrode. This makes it possible to prepare very thin films of nickel‐based modified electrodes. In cyclic voltammetry experiments the Ni‐CME exhibits a pH dependence of the peak potentials typical of the α‐Ni(OH)2/γ‐NiOOH redox process, and a separation between anodic and cathodic peak potentials of 64mV at pH 13.2 and 10 mVs−1. The redox catalysis at Ni‐CMEs of representative compounds that are not easily electrooxidized, such as choline, cadaverine, γ‐amino butyric acid (GABA), benzyl alcohol, and glycine, is demonstrated. The good stability of these nickel‐based modified electrodes makes them attractive in analytical applications.