Electrochemiluminescence of hydrogen peroxide-luminol at a carbon electrode

Electrochemiluminescence (ECL) was used to detect hydrogen peroxide in aqueous solutions in the presence of electrolytically oxidized luminol. Using a glassy carbon electrode, the ECL mechanism could be selected by the applied potential. Luminol is oxidized to the excited intermediate (diazasemiquinone radical or diazaquinone) at around 0.5 V vs. SCE in pH 7.4 aqueous solution; above 1.0 V, hydrogen peroxide is oxidized to superoxide and the amino group of luminol is also oxidized. Therefore, the ECL mechanism is different depending on whether the applied potential is between 0.5 and 1.0 V or more positive. At the higher potentials, complex fluorophores are involved. On the other hand, at the low potentials the fluorophore is simple and the ECL spectrum shows a simple maximum emission peak. The quality of the data obtained at 0.7 V is better than that at 1.2 V. The detection limit of hydrogen peroxide is 66 pmol with a relative standard deviation of 1.1% (n = 5) at a signal-to-noise ratio of 6.