Determination of trace amounts of nickel by differential pulse adsorptive cathodic stripping voltammetry using calconcarboxylic acid as a chelating agent

A method for the determination of nickel(II) by stripping voltammetry is described. The method is based on the adsorptive accumulation of nickel(II) calconcarboxylic acid complex onto a hanging mercury drop electrode (HMDE), followed by the reduction of the adsorbed complex using differential pulse voltammetry. The optimum operating conditions and parameters were found to be 0.05 M NH3/NH4Cl buffer (pH = 9.5) as the supporting electrolyte, a ligand concentration of 1 x 10(-6) M, accumulation potential of -0.5 V (vs. Ag/AgCl) and accumulation time of 60 s. At the optimized conditions, the peak current is proportional to the concentration of nickel in the range of 1.7 x 10(-9) to 4.7 x 10(-7) M (0.1-28 ng ml(-1)) with a detection limit of 0.05 ng ml(-1). The relative standard deviation (n = 10) at nickel concentrations of 2, 10 and 15 ng ml(-1) varies in the range 0.76 to 2.1%. Possible interferences by metal ions, which are of great significance in real matrices, have been studied. The method was successfully applied to the determination of nickel content in a chocolate sample.