An automated in-chip-catalytic–spectrophotometric method for determination of copper(ii) using a multisyringe flow injection analysis-multipumping flow system

Abstract

In this work a fully automated catalytic–spectrophotometric method for determination of copper at trace levels using a multisyringe flow injection system (MSFIA) and a multipumping flow system (MPFS) coupled to a micro-chip (Chip–MSFIA–MPFS) is presented. The reaction is based on the catalytic effect of Cu(II) on the oxidation of the in situ reduced form of 2,6-dichlorophenolindophenol (DCPI)_r, by hydrogen peroxide. Due to the importance of the mixing order of the reagents, a new design of the chip is proposed. DCPI, ascorbic acid and buffer are first propelled to mix in the front section of the chip using MPFS. Then this reagent mixture, together with hydrogen peroxide and the sample, is simultaneously dispensed to the rear section of the chip by using a multisyringe for mixing, heating and absorbance measurement of the product at 600 nm. The optimum conditions are 0.9 mmol L⁻¹ DCPI, 3.6 mmol L⁻¹ ascorbic acid, 0.8 mol L⁻¹ ammonium chloride buffer, pH 10.5, and 0.3 mol L⁻¹ H₂O₂. The proposed system is simple, rapid, selective and sensitive. We can determine trace levels of Cu(II) at room temperature (25 °C). The main analytical characteristics of the proposed method are a detection limit of 0.12 μg L⁻¹ of Cu(II), a working range of 0.4–35.0 μg L⁻¹ of Cu(II), and a relative standard deviation of 0.79% (10 μg L⁻¹ Cu(II), n = 15). The system was successfully applied to water samples, certified reference materials (CRMs) of river and waste water, acid digested multivitamins and animal tissues with a sample throughput of 31 injections h⁻¹.