Flow-injection determination of copper(II) based on its catalysis on the redox reaction of cysteine with iron(III) in the presence of 1,10-phenanthroline

A redox reaction of cysteine with iron(III) proceeds slowly in the presence of 1,10-phenanthroline (phen). However, this reaction is accelerated in the presence of copper(II) as a catalyst, producing an iron(II)–phen complex (λmax=510 nm). A sensitive spectrophotometric flow-injection method is proposed for the determination of copper(II) based on its catalytic action on this redox reaction. The dynamic range was 0.1–10 ng ml–1 of copper(II) with a relative standard deviation of 1.0% (n=10) for 1.0 ng ml−1 of copper(II) at a sampling rate of 30 h–1. The detection limit (S/N=3) is 0.04 ng ml–1. The proposed method was successfully applied to the determination of copper in river water as a certified reference material.