Flow-injection/standard subtraction method for the determination of iron(III) based on its catalytic effect and inhibition of EDTA Original Research Article

A new approach for the flow-injection catalytic determination of 10−6 M levels of iron(III) is proposed. This method is based on the catalytic effect of iron(III) on the oxidative coupling of p-anisidine with N,N-dimethylaniline to form a blue compound (λmax=735 nm) in the presence of hydrogen peroxide and 1,10-phenanthroline as an activator, and the inhibitory effect of EDTA on the iron(III)-catalyzed reaction. The concentration of iron(III) can be determined from only two flow signals which are obtained by injecting the iron(III) and iron(III) plus EDTA solutions into the flow lines without a calibration graph for iron(III); this procedure may be called standard subtraction. The proposed method permits the analysis of 12 samples per hour (24 peaks per hour) and was successfully applied to the determination of iron in standard iron ore samples.