Detection of Radicals Generated by Strong Oxidants in Acidic Media

A new method to study superoxide and hydroxyl radicals in aqueous solution in the pH range 1 to 6 is described and critically evaluated. The method primarily detects superoxide, which reacts with tetranitromethane (TNM) by reductive cleavage. The strongly coloured nitroform anion (ε350nm = 15000M−1 cm−1) formed, is easily measured in a spectrophotometer or in a stopped-flow equipment. Hydroxyl radicals are measured indirectly. In a first step the hydroxyl radical reacts with iso-propyl alcohol to give acetone and superoxide. The superoxide formed is then in a second step detected with TNM. The TNM-method was primarily designed to monitor the radical formation under ozone bleaching conditions, but it is also applicable in acidic hydrogen peroxide.