MERCURY FILMS ON A GLASSY-CARBON SUPPORT - ATTRIBUTES AND PROBLEMS

The main problems associated with the preparation and application of mercury film electrodes on a glassy carbon support (MFGCE) are outlined. The role of the GC support material and in particular of the surface condition (microstructure and polishing procedure) for deposition of homogeneous mercury films and the proper performance of the resulting MFGCE in stripping voltammetric measurements is exploited. Highly polished electrodes without surface defects were found to be unsuitable because elemental mercury does not adhere to the GC surface. Instead, defined roughening of the GC support is proposed and is shown to yield mechanically stable films with excellent electrochemical characteristics. It is further shown that properly prepared MFGCEs may quickly lose their performance characteristics owing to fouling. The main reasons can be attributed to mechanical deterioration, formation of surface layers of insoluble mercury(I) compounds, adsorption of polymeric organic compounds and oversaturation with the mercury film by elements that form irreversible amalgams or intermetallics. The respective interferences are manifested in decreased sensitivity, increased background currents, loss of hydrogen overvoltage, impairment of peak resolution of adjacent signals or even totally erratic behaviour. The advantages of flow-through stripping voltammetry in minimizing or even avoiding these kinds of interferences are emphasized.