The Dropping Mercury Electrode
The first of the hydrodynamic techniques developed was the Dropping Mercury Electrode (DME). In this arrangement a fine capillary is connected to a reservoir of mercury. The cell is designed so that mercury is allowed to flow down the capillary at a controlled rate and out into the solution.
Electrical contact to the mercury is made in the reservoir and a reference and counter electrode are sited in the electrolyte solution. Voltammetry can performed in an identical manner to that described earlier, however, now the electrode is constantly changing area and so a linear sweep voltammogram will exhibit significantly different behaviour. The current can be seen to go through a series of peaks and troughs as the voltage is swept. As the mercury drop grows the surface area accessible to the electrolyte also increases and consequently the current increases. However, at some point the Mercury drops from the tip leaving a small new area in contact with the electrolyte, consequently the current drops rapidly at this point before gradually increasing as the drop grows again. This behaviour is repeated throughout the scan. Clearly this process is not something that is easily predicted and the fluid dynamics are still not fully understood for this particular device. However, this technique proved very popular due to the ability to continually refresh the electrode surface during the experiment.