The determination of trace levels of iron in seawater using adsorptive cathodic stripping voltammetry

A sensitive procedure to determine trace levels of iron in seawater is proposed which utilizes adsorptive deposition of the complex of Fe(III) with 1-nitroso-2-naphthol (1-N-2-N) on the mercury drop electrode. Optimized conditions include a solution concentration of 20-mu-M 1-N-2-N and a pH of 6.9; an adsorption potential of -0.25 V is applied, and the potential scan is in the linear sweep mode. The limit of detection is 0.2 nM Fe using a deposition time of 10 minutes. Peak instability due to adsorption of Fe(III) on either the voltammetric cell or rejected mercury drops is eliminated by addition of hydroxylammonium, which reduces the dissolved Fe(III) to Fe(II). The reaction mechanism of the analytical procedure therefore includes oxidation of Fe(II) to Fe(III) at the electrode surface with the subsequent complexation by 1-N-2-N and adsorption on the mercury drop; the reduction current of the adsorbed and complexed Fe(III) is then measured.