Kinetic analysis of the Fenton reaction by ESR-spin trapping.

A quantitative analysis of hydroxyl radical (.OH) generated in the Fe(2+)-hydrogen peroxide reaction system was explored by a spin-trapping method using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) combined with electron spin resonance spectroscopy. Based on the numerical analysis of Fenton-related reactions, the reduction of DMPO-OH adduct from 1:1 stoichiometry prominent at high concentrations of Fe2+ was consistent with a reaction model in which a molar amount of hydrogen peroxide was reduced by two molar amounts of Fe2+. Furthermore, time-dependent decrease in DMPO-OH quantity, apparent at much higher concentration of Fe2+, was proved due to the reaction not with Fe2+ but with Fe3+.