Simultaneous determination of iron, copper, and cadmium by adsorptive stripping voltammetry in the presence of thymolphthalexone

A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of iron, copper and cadmium is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of iron, copper and cadmium were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 2.0 mu M, pH of 9.5, and accumulation potential at -0.4 V vs. Ag/AgCl with an accumulation time of 60 s. The peak currents are proportional to the concentration of iron, copper and cadmium over the 1 - 80, 0.5 - 100 and 1 - 100 ng mL(-1) ranges with detection limits of 0.5, 0.4 and 0.9 ng mL(-1), respectively. The R.S.D. at a concentration level of 20 ng mL(-1) of iron, copper and cadmium were 2.5%, 0.9% and 1.5% (n=6), respectively. The procedure was applied to the simultaneous determination of iron, copper and cadmium in the tap water and some synthetic samples with satisfactory results.