Electroluminescent method for determining hydrogen peroxide and peroxydisulphate ions in aqueous solution using TiO2 film electrodes

An electrochemical optical sensor system with luminescence response was proposed for the continuous determination of hydrogen peroxide or peroxydisulphate concentration in aqueous solutions. The electroluminescence (EL) of TiO2 film electrodes, which arises under conditions of the cathodic polarization as a result of the hole injection into the TiO2 from high-energy OH. or SO4-. radicals produced by the electroreduction of H2O2 or S2O82- ions on the electrode surface, was used as the analytical signal. The EL response is linearly related, in a logarithmic scale, to the hydrogen peroxide or peroxydisulphate concentration ranging from 10(-3) to 10(-1) M H2O2 and from 5 x 10(-4) to 1 M Na2S2O8. It was shown that a substantial increase in the quantum efficiency of the EL and, as a consequence, in the sensitivity of the sensor system can be achieved by doping TiO2 films with chromium. The potential dependence of the EL spectrum for TiO2 electrodes in S2O82- solutions differs essentially from that in H2O2 solutions which allows measurement of the concentration of S2O82- ions when they coexist with H2O2 in solution.