A chemiluminescence method for the detection of electrochemically generated H2O2 and ferryl porphyrin

Electrochemical formation of H2O2 and the subsequent ferryl porphyrin were examined by measuring luminol chemiluminescence and absorption spectrum using flow-injection method. Emission was observed under the cathodic potential (0.05 Vat pH 2.0 and -0.3V at pH 11.0) by the electrochemical reduction of buffer electrolytes solution but no emission was observed at anodic potentials. (FeTMPyP)-T-III solution was added at the down stream of the working electrode and was essential for the emission. Removal of dissolved O-2 resulted in the decrease of emission intensity by more than 70%. In order to examine the lifetime of reduced active species, delay tubes were used in between working electrode and (FeTMPyP)-T-III inlet. Experimental results suggested the active species were stable for quite long. The emission was quenched considerably (> 90%) when hydroperoxy catalase was added at the down stream of the working electrode whereas SOD had little effect. Significant inhibition of the emission by the addition of alkene at the down stream of the (FeTMPyP)-T-III inlet was considered as evidence of oxo-ferryl formation. The spectra at reduction potential under aerated condition were shifted to the longer wavelength (> 430 nm) compared to the original spectrum of (FeTMPyP)-T-III (422 nm). All the spectra were perfectly reproduced by a combination of (FeTMPyP)-T-III and O=(FeTMPyP)-T-IV (438 nm) spectra. These observations lead to the conclusion that H2O2 was produced first by electrochemical reduction of O-2, which then converted (FeTMPyP)-T-III into O=(FeTMPyP)-T-IV to activate luminol. The current efficiencies for the formation of H2O2 were estimated as about 30-65% in all over the pH. (c) 2005 Elsevier B.V. All rights reserved.