Determination of copper(II) in a complex matrix after prereduction to copper(I) in a flow-injection system with an amperometric detector

A flow-injection system with a carbon paste detector is proposed for the determination of copper in complex media at +0.050 V vs. Ag/AgCl. Both the reduction current peak of Cu(II) and the oxidation peak of Cu(I) (obtained in the presence of hydroxylamine in the reagent stream) were proportional to the Cu(II) concentration in the original sample. The stabilization of Cu(I) in the hydroxylamine system provides a novel approach; the inherent repeatability of operation of flow-injection systems (timing, etc.) proved ideal for this utilization. Acidified Cu(II) samples containing additional metal ions [Fe(lI), Zn(II), Pb(II)] and relatively high concentrations of serum albumin were analysed. A chelating column retained heavy metal ions while allowing albumin to run to waste. The retained metals were subsequently eluted with nitric acid into a stream of sodium acetate or sodium acetate-hydroxyl- amine. Before reaching the detector, the pH of the sample plug was adjusted. With the hydroxylamine system, Fe(III) interference was minimized and the sensitivity and reproducibility were improved. The sample throughput was 25 h^?1. National Bureau of Standards Standard Reference Material 909 Human Serum was used to test the method.