Oxidation of azide anion at boron-doped diamond thin-film electrodes

The oxidation of dissolved inorganic azide anion in aqueous media was investigated using high-quality, boron-doped diamond thin-film electrodes. Linear sweep and differential pulse voltammetry, along with now injection analysis in the amperometric detection mode, were used to study the reaction at neutral pH as a function of the potential sweep rate, analyte concentration, and electrolyte composition. Comparison experiments were performed using polished glassy carbon. Azide undergoes an irreversible oxidation (1 e(-)/equiv) at both of these carbon electrodes, presumably with nitrogen as the primary product. A linear dynamic range of 3-4 orders of magnitude and a detection limit as low as 0.1 mu M (4.3 ppb) at a S/N = 3 were observed for diamond in the voltammetric measurements. The now injection analysis results for diamond indicated a linear dynamic range of 5 orders of magnitude and a detection limit of 8 nM (0.3 ppb) at a S/N = 3. The diamond response was generally reproducible from film to film, and the background signal and signal-to-background ratio were extremely stable for up to 12 h of continuous use. The results demonstrate that this new electrode material serves as an analytically useful substrate for the detection of azide anion and exhibits superior performance characteristics compared with glassy carbon.