Development of a flow injection method with amperometric detection for the indirect determination of copper in drinking water samples

A gas-diffusion flow injection method with amperometric detection for the indirect determination of copper on a silver electrode was developed. The flow through system was equipped with two injection valves and a gasdiffusion unit. In the first step, a signal of a cyanide solution was recorded. In the subsequent step, the signal of cyanide in the presence of copper was measured. Interferences (Cd(II), Co(II), Ag(I), Ni(II), Fe(III), Hg(II) and Zn(II)) were investigated and successfully removed. The calibration graph was linear in the range 1–90 μmol dm-3 of copper with a correlation coefficient of 0.993. The regression equation is I = (0.0455±0.0015)c + (0.4611±0.0671), where I is the relative signal decrease in μA and c is concentration in μmol dm-3. Relative standard deviation for six consecutive injections of 30 μmol dm-3 copper(II) was 1.47 % and for 1 μmol dm-3 copper(II), it was 3.40 %. The detection limit, calculated as 3 s/m (where s is a standard deviation of nine measurement of a reagent blank and m is the slope of the calibration curve), was 0.32 μmol dm-3, which corresponds to 2.44 ng of copper(II) (the loop volume was 0.12 cm3). The method enables 60 analyses per hour and it was successfully applied for the determination of copper in drinking water samples.