Voltammetric and microscopical investigation of the properties and behaviors of individual mercury micro-droplets

Mercury film modified electrode based stripping voltammetry has become a rapid and low cost method in routine trace element environmental analysis. However, the understanding of the physical and chemical properties of the plated mercury film still needs to be enhanced till now. It has been recognized that the so-called mercury film actually consists of numerous micro mercury droplets, so it is of significant importance to directly investigate the properties and behaviors associated with the individual droplet. Thus, a platinum ultramicroelectrode was used as the substrate for mercury plating, and only one mercury droplet is formed under this condition. Herein, Fourier Transformed Sinusoidal Voltammetry (FTSV) was employed to investigate both the growth process of a mercury droplet and the behaviors of the droplet after plating. Meanwhile, an optical microscope was used to provide direct visual observation. Investigation suggests that: (a) Both the gradual growth process and the fast coalescence event of individual mercury droplet can be resolved with FTSV; (b) The plated mercury droplet can be partially oxidized immediately after the disconnection between the working electrode and the potentiostat in some circumstances, e.g. the presence of trace amount of chloride ion. The present study not only sheds new light on the properties of mercury film electrode but also demonstrates the feasibility of employing FTSV as a new tool for the characterization of micrometer or even nanometer sized particles.