The Rotated, Mercury-Coated Platinum Electrode: Preparation and Behavior of Continuously Deposited Mercury Coatings and Applications to Stripping Analysis

A reproducible, thin-mercury-film, rotated electrode can be prepared by continuously plating at constant current a rotated platinum electrode with mercury from a Hg(II) solution in 0.1M nitric acid. The use of a large, constant plating current permits high hydrogen overvoltages to be obtained. Mercury plating efficiencies of the order of 75% are attainable. The application of this electrode to the stripping analysis of thallium in the concentration range 2 × 10⁻⁷ to 8 × 10⁻⁵M and lead in the concentration range 2 × 10⁻⁷ to 1 × 10⁻⁶M is reported and the limitations of the technique are discussed. Both lead and thallium are deposited simultaneously with mercury and are stripped by chemical oxidation of the amalgam with Hg(II). The chronopotentiogram obtained during the chemical stripping process is used to determine the concentration of lead and thallium in their mixtures. The rate of the reaction between thallium amalgam and Hg(II) is rapid compared to the rate of supply of Hg(II), while the reaction of Pb with Hg(II) is complicated by a slow chemical step.