Determination of Hydroperoxyl/superoxide Anion Radical (HO 2 · /O 2 ·- ) Concentration in the Decomposition of Ozone Using a Kinetic Method

A novel kinetic method for determination of HO 2 · /O 2 ·- in ozone decomposition in water is described. In this study, potential interferences of O 3 and the hydroxyl radicals, ˙OH (O3) , are suppressed by HSO 3 - /SO 3 2- . HO 2 ˙/ O 2 ˙ - formed in ozone decomposition reduces Fe 3+ -EDTA into Fe 2+ -EDTA and subsequently the well-known Fenton-like (FL) reaction of H 2 O 2 and Fe 2+ -EDTA produces the hydroxyl radicals, ˙OH (FL) . Benzoic acid (BA) scavenges OH( FL ) to produce OHBA, which are analyzed by fluorescence detection (λ ex = 320 nm and λ em = 400 nm). The concentration of HΟ 2 ˙/O 2 ˙ - in ozone decomposition has been determined by the novel kinetic method using the experimentally determined half-life (t 1/2 ). The steady-state concentration of HO 2 ˙/O 2 ˙ - is proportional to the O 3 concentration at a given pH. However, the steady-state concentration of HO 2 ˙/O 2 ˙ - in ozone decomposition is inversely proportional to pH values. This pH dependence is due to significant loss of O 2 ˙ - by O 3 at higher pH conditions. The steady-state concentrations of HO 2 ˙/O 2 ˙ - are in the range of 2.49 (± 0.10) × 10 -9 M (pH = 4.17) ∼ 3.01 (± 0.07) x 10 -10 M (pH = 7.59) at [O 3 ] o = 60 μM.