Detection of hydroxide ions in aqueous solutions by steady-state voltammetry

The electrochemical oxidation of hydroxide ions on microdisk electrodes was studied to find the conditions where the steady-state current can be used for analytical applications. Results are presented for the dependence of th e voltammetric response on the microdisk radius, the electrode material and the hydroxide concentration. Well-defined waves for hydroxide oxidation we re obtained under steady-state conditions with all microdisks employed. How ever, the steady-state wave splits for some hydroxide concentrations and ra dii, but the overall current is still proportional to the concentration. Th e usefulness of the wave for analytical applications depends on the electro de material. Although the wave is seen on nickel, platinum and gold the lat ter is the most promising for the amperometric detection of basicity of aqu eous solutions. On platinum, the wave can be used but the plateau is not so well defined. On nickel, oxide formation makes measurements difficult. Und er steady-state conditions a well-defined wave attributed to the direct oxi dation of hydroxide ions was also observed on a gold rotating disk electrod e. The wave height was found to be proportional to the square root of the r otation speed, thus indicating that the process was under diffusion control . The limiting current was also found to be proportional to the concentrati on of hydroxide ions over the range 0.05-10 mM.