No abstract

We report on a novel voltammetric detection of oxalic acid by using glassy carbon electrodes with covalently attached nitrogen-containing functional groups prepared by stepwise electrolysis. A glassy carbon electrode electrooxidized in an ammonium carbamate solution was electroreduced at -1.0 V (vs. Ag/AgCl) in 1.0 M sulfuric acid for a long time. We found that the electrocatalytic oxidation wave of oxalic acid obtained by this modified glassy carbon electrode was moved to a more negative potential region than that obtained by a platinum electrode in an acidic medium. A good linearity for the peak current signals was observed in the concentration range from 0.1 to 50 mM.

Electrocatalytic oxidation activity of oxalic acid can be observed by using a multielectrolytic modified glassy carbon electrode (MMGCE). The MMGCE was fabricated by using the following electrolytic-oxidation/reduction processes. First, the functional groups containing nitrogen atoms such as amino group are introduced by the electrode oxidation of a bare glassy carbon electrode in an ammonium carbamate aqueous solution, and next, this electrode was electroreduced in sulfuric acid, and it was found that the reduction current gradually increased as the electrolysis time increased. This suggests that functional groups containing nitrogen atoms contributing the catalytic electron transfer of hydrogen ion are introduced. To observe the electrode oxidation wave of oxalic acid, the voltammmetric measurements of oxalic acid was carried out by using MMGCE in an acidic medium. The oxidation wave of oxalic acid at low potential range was appeared in the linear sweep voltammograms. The MMGCE exhibited well-defined peak of oxalic acid oxidation in acidic medium.