Abstract: In hydrochloric acid solution of pH=3.2, ferrum(Ⅲ) can oxidize I- into the form of I-3 and acridine red(AR) can react with I-3 to form of AR-I3 ion association complexes(the composition stoichiometry was defined as n(I-3)∶n(AR)=1∶1). The association complexes automatically aggregate to (AR-I3)n association particles. In this case, the resonance light scattering(RLS) intensities are enhanced greatly. The maximum RLS wavelength locates at 468 nm. The optimum conditions of the reaction, influence factors and the effect of coexisting substances were investigated. In addition, the reaction mechanism of the ion-association complex was discussed. The resonance scattering intensity(ΔI468 nm) was linearly related to the concentration of ferrum(Ⅲ) in the range of 0.08～0.56 mg/L with a detection limit of 5.76×10-7 g/L. The assay was applied to the detection of trace ferrum(Ⅲ) in realistic samples, with a RSD of 3.3% and the recovery range of 96.0%～102.4%, and the results were in a good agreement with that of atomic absorption spectrometry assay.

Key words: acridine red, resonance light scattering, association particle, Ferrum(Ⅲ)