Ferrous ion oxidations by √H, √OH and H2O2 in aerated FBX dosimetry system

In the ferrous ion, benzoic acid and xylenol orange (FBX) dosimetric system, benzoic acid (BA) increases the G(Fe³⁺) value. Xylenol orange (XO) controls the BA sensitized chain reaction as well as forms a complex with Fe³⁺. In the aerated FBX system each √H, √OH and H₂O₂ oxidizes 8.5, 6.6 and 7.6 Fe²⁺ ions, respectively; and these values respectively increase to 11.3, 7.6 and 8.6 in oxygenated solution. About 8% √OH reacts with XO and the remaining with BA. The above fractional values are due to this competition. This √OH reaction with XO oxidizes 1.8% and 2.1% ferrous ions only in aerated and oxygenated solutions, respectively. There is a competition between √H reactions with O₂ and with BA, but both lead to the production of H₂O₂. The oxidation of Fe²⁺ by √OH reactions at different concentrations of H₂O₂ is linear with absorbed dose while the √H reactions make the oxidation of Fe²⁺ non-linear with dose. This is due to competition reaction of H-adduct of BA between O₂ and Fe³⁺.