Determination of hydroperoxyl/superoxide anion radical (HO2./O2.-) concentration in the decomposition of ozone using a kinetic method

Abstract

A novel kinetic method for determination of HO2./O2.- in ozone decomposition in water is described. In this study, potential interferences of O3 and the hydroxyl radicals, .OH(O3), are suppressed by HSO 3-/SO32-. HO2./O2.- formed in ozone decomposition reduces Fe3+-EDTA into Fe2+-EDTA and subsequently the well-known Fenton-like (FL) reaction of H2O2 and Fe2+-EDTA produces the hydroxyl radicals, .OH(FL). Benzoic acid (BA) scavenges .OH(FL) to produce OHBA, which are analyzed by fluorescence detection (λex = 320 nm and λem = 400 nm). The concentration of HO2./O2.- in ozone decomposition has been determined by the novel kinetic method using the experimentally determined half-life (t1/2). The steady-state concentration of HO 2./O2.- is proportional to the O3 concentration at a given pH. However, the steady-state concentration of HO2./O2.- in ozone decomposition is inversely proportional to pH values. This pH dependence is due to significant loss of O2.- by O3 at higher pH conditions. The steady-state concentrations of HO2./O 2.- are in the range of 2.49 (± 0.10) × 10-9 M (pH = 4.17) ∼ 3.01 (± 0.07) × 10 -10 M (pH = 7.59) at [O2]o = 60 μM.