The Silver Electrode in Square-Wave Anodic Stripping Voltammetry. Determination of Pb2+ without Removal of Oxygen

A silver rotating disk electrode is used for the determination of lead in concentrations from 2 × 10 - 9 to 3 × 10 - 7 M by square-wave anodic stripping voltammetry (SWASV) without removal of oxygen. The repeatability of consecutive SWASV runs in synthetic solutions covering the entire concentration range is better than 2%. The calibration curve is represented by a correlation coefficient of at least 0.999. The detection limit for a 2-min electrodeposition is 0.5 nM. Up to 600 runs can be carried out on synthetic solutions without any pretreatment of the electrode. A 4-fold excess of Cd 2+ and a 10 000-fold excess of Cu 2+ do not interfere with the determination of part-per-billion concentrations of Pb 2+ . Surfactants present in tap water distort the SWASV. Improvement of the analytical response in tap water is achieved by pretreatment of the samples: irradiation at 254 nm or digestion with HNO 3 . During anodic stripping voltammetry in the concentration range studied, a uniformly distributed submonolayer of lead, occupying 0.02%−1% of the real surface of the electrode, is formed by underpotential deposition. Linearity in calibration plot is achieved up to 1% electrode coverage; in terms of the experimental parameters of the deposition step (rate of rotation and time of electrolysis), this condition for linearity is C Pb 2+ N 1/2 t d ≤ 2.2 × 10 5 nM rpm 1/2 s.