Kinetic method for the determination of trace amounts of copper(II) in water matrices by its catalytic effect on the oxidation of 1,5-diphenylcarbazide

The chemical reaction between Cu(II) and 1,5-diphenylcarbazide (DPC) is revised from an analytical perspective. It is shown that instead of a Cu-DPC complex, an oxygen mediated DPC oxidation to diphenylcarbazone (DPCO) is the main reaction involved where Cu(II) acts as catalyst. Therefore, the signal observed corresponds to the oxidation product DPCO. Under certain specific conditions a chelate complex between Cu(II) and DPCO can also be observed. Kinetic parameters of these reactions are calculated. These results set the basis for the development of analytical methodologies for the determination of Cu(II) at ultra-trace levels. Since the study of interferences revealed Mg(II) as the most serious, an optimised flow injection system which allows the in-lineelimination of Mg(II) is presented. The limit of detection (k = 3) calculated for 10 blank replicates is 0.05 μg L−1 (injection volume 20 μL), the analytical sensitivity equals 48 μg−1 L and the sample throughput is 120 h−1. Obtained results for Cu(II) determination in natural waters as well as the validation of the analytical methodology will be given and discussed.