Improved catalytic photometric determination of iron(III) in cetylpyridinium premicellar aggregates

Abstract Premicellar aggregates of the cationic surfactants cetylpyridinium chloride (CPC) enhance the catalytic activity of iron(III) on the oxidation of sulphanilic acid by potassium periodate in the presence of 1,10-phenanthroline as activator. The aggregates however have no effect on the uncatalysed reaction. The kinetic study presented in this paper shows that the effects of CPC on the iron(III)-catalysed reaction can be entirely attributed to increased reactant concentrations in the surfactant micelle subunits. The iron(III) effective concentration in the reaction medium is increased by formation of a transient catalyst-sulphanilic acid complex in the catalytic cycle which concentrates on the premicellar aggregates. Such an effect of CPC was exploited for the kinetic photometric determination of iron(III) over the linear range 0.1–4.0 × 10 −7 M with a detection limit of 3.37 × 10 −9 M. (i.e., 7 times lower than that of the method using an aqueous medium). The relative precision for 2.0 × 10 −7 M of iron(III) was 5%. The proposed method is highly sensitive and selective and was applied to the determination of iron in blood serum samples.