Coulometric and Preparative Electrochemistry

A bridge compartment with sufficient hydrostatic head to ensure that fresh electrolyte flows continuously into both the working-electrode and counterelectrode compartments is another useful approach.35 However, the volumes of the solutions in both compartments increase inconveniently during a titration. This method also suffers if the background electrolyte contains reactive impurities (e.g., oxygen). 

The problem of adequate isolation has been studied theoretically and practically in the context of coulometric titrations.36 The loss of sample by diffusion will not be greater than 0.1% if at least two fine-frit separators are used with at least 4-5 cm of electrolyte between the frit and if the time of electrolysis is short (3-15 min). A tube closed with a fine frit that contains a 12-mm layer of fine silica gel above the frit has been suggested. 

Ion-exchange membranes have been used as separators,37 38 particularly in coulometric titrations. The fixed negative charge of a cation-exchange membrane tends to exclude anions, so that current through the membrane is due primarily to cation transport with the reverse true for anion-exchange membranes. 

Other devices may be useful. For example, if the counter electrode is the 

Another factor to consider is the resistance heating of the electrolyte. In the example cited, 10 W of power is dissipated by passing 100 mA through a cell with 1000 12 of resistance. This is sufficient to raise the temperature of the electrolyte significantly unless provision for cooling is made. Finally, large 

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