Studies on electrochemical reactions at metal‐oxide electrodes for combination with high‐performance liquid chromatography

Abstract

Various electrodes, such as nickel, copper, and cobalt metal electrodes and nickel‐, copper‐, and cobalt‐modified glassy‐carbon electrodes, are investigated for the oxidative amperometric detection of alcohols, polyols, and carbohydrates after separation by high‐performance liquid chromatography (HPLC). These electrode materials are compared with respect to stability, detection limits, and an eventual necessity of electrode surface pretreatment. Detection limits of 4 ng and 10 ng glucose injected can be achieved using a metallic copper electrode and a metallic nickel electrode, respectively. Investigations at the surface of a nickel electrode reveal the existence of a reversible layer of nickel oxide with higher valence which is formed in an alkaline medium at an applied potential of at least 400 mV versus Ag/AgCl/KCl(sat). Its thickness strongly depends on electrochemical pretreatment procedures. This layer can be converted into a layer of lower valence nickel oxide either electrochemically or chemically. Investigations of the electrode surface are carried out by in situ ultraviolet‐visible (UV‐vis) reflectance spectroscopy and by Fourier‐transform infrared spectroscopy (FTIR). Controlled‐potential experiments at various metal‐oxide electrodes and separation of the oxidation products on ion‐exchange columns reveal some of the reaction mechanisms for the oxidation of alcohols, polyols, carbohydrates, and similar organic compounds.