Novel catalytic oxidative coupling reaction of N,N-dimethyl- p-phenylenediamine with 1,3-phenylenediamine and its applications to the determination of copper and iron at trace levels by flow injection technique

Abstract

A new catalytic oxidative coupling reaction of N,N-dimethyl- p-phenylenediamine (DPD) with 1,3-phenylenediamine (mPD) in the presence of hydrogen peroxide has been developed for trace metals analysis. The rate of the oxidation/coupling reaction can be enhanced significantly by iron, copper and cobalt. These metal ions can catalyze the oxidation reaction of DPD to form an oxidized product; the oxidized DPD was then coupled with mPD to give a blue-colored product which was measured spectrophotometrically at 650 nm. On the basis of such a reaction scheme, two simple flow injection analysis methods for the determination of copper and iron have been developed. Detailed studies on chemical and FIA variables affecting the sensitivity of the detection were carried out. Interferences from several ionic species were examined for the determination of copper: the interference effect by Fe(III) and Fe(II) up to 1.5 mg L −1 was successfully suppressed by pretreating sample with ammonium acetate buffer solution (pH 8.4). Good linearity of a standard calibration graph was obtained over the ranges of 0–8 and 0–2 μg L −1 of copper and iron, respectively, and the detection limits were 0.05 and 0.02 μg L −1 for copper and iron, respectively. The precision of the methods in terms of relative standard deviation were 1.4 and 1.5% of R.S.D. which were obtained from 10 injections of 2.0 and 1.0 μg L −1 of standard copper and iron, respectively. The proposed methods were successfully applied to the determination of copper and iron in tap and river water samples. The accuracy of the proposed methods was assessed by the analysis of certified reference material of river water.