Simultaneous spectrophotometric determination of copper(II) and zinc(II) based on their kinetic separation in flow-injection systems

Flow-injection methods are developed for the spectrophotometric analysis of binary copper(II) and zinc(II) mixtures. They are based on measurements of a differential kinetic signal caused by ligand-exchange reactions that occur in the flow between the complexes of these metals with the same chromogenic reagent (4-(2-pyridylazo)-resorcinol or zincon) and aminopolycarboxylic acids. Two different approaches are used for the kinetic separation (or masking) of these metals followed by the on-line processing of the recorded signal by regression analysis. One of them is monitoring an indicator reaction in the stopped-flow mode, and the other is recording the separated peaks in the flow-injection system with two reaction zones reaching the detector over certain periods. The optimum detection conditions were found (c _min = 0.03 μg/mL), which allow the detection of the studied metal ions in mixtures in a ratio of no more than 1: 5 with a relative error of no more than 5%, good precision (RSD < 10%, n = 6, P = 0.95), and high throughput (90 h^?1). The developed procedures were tested in the analysis of model mixtures and pharmaceutical preparations.