Preparation of Silver-Based Mercury Film Electrodes for Anodic Stripping Voltammetry

The aim of this study was to develop an electrochemical method for reproducible preparation and evaluation of silver-based mercury film electrodes (SBMFE) for applications such as anodic stripping voltammetry of transition metals and lanthanides. The mercury film was electrochemically deposited on a silver disk electrode and the thickness and reproducibility of the deposited mercury film was determined by using a controlled electrochemical dissolution in a Na2EDTA and acetate buffer solution. Though this electrochemical dissolution method was previously used by other authors in the past, it was specifically optimized for this application. Upon optimization we have shown a correlation between the dissolution charges and mercury film thickness. Additionally, this study also aimed to expand the current understanding of the role of the silver amalgam formation process of the stability and aging of the mercury film. Previous work has confirmed that the mercury film has a finite lifetime that is related to the thickness of both the mercury film and the amalgam. However, while it is known that the film degrades with time, the impact that film thickness and rate of amalgamation have on the lifetime and performance stability of the mercury film is not understood. Moreover, though increased stability of the mercury film when deposited on an amalgam has been noted in previous studies, no work has been done to provide quantitative results for the effect of the amalgam on the film’s longevity. The controlled removal of the mercury film allows for accurate quantitative analysis to determine the amount of mercury in the film and stability when used with electroanalytical techniques such as anodic stripping voltammetry. Moreover, without completely removing the mercury film before a new deposition the mercury film thickness can increase at an unpredictable rate and thus hindering the performance and reproducibility of results. Therefore, electrochemically removing the mercury film without harming the amalgam is ideal for the performance stability of the electrode. This work provides quantitative results for the effect of the amalgam on the films longevity and performance. The continuous monitoring of the performance and stability of the SBMFE in anodic stripping voltammetry applications confirmed a definitive impact of the formation and growth of the solid silver amalgam at the Ag/Hg interface. More specifically, we demonstrated the performance and stability of SBMFE clearly increases with a thicker silver amalgam. Moreover, the impact of the mercury film thickness was also evaluated to achieve the required thin layer behavior during the anodic stripping voltammetry experiments. In conclusion, we have established an extensive protocol for the preparation of reliable and reproducible SBMFE as well as demonstrated an electrochemical method to quantitatively remove the mercury film without harming the amalgam. Moreover, we found that the expected dissolution charge is twice the deposition charge, which can be accurately predicted based on the deposition charge. Additionally, we have determined the performance stability of the SBMFE over several days of use in anodic stripping voltammetry of metals and have correlated the results with the time dependence of the amalgamation rate.