Controlled-potential coulometry, also known as potentiostatic coulometry, employs a three-electrode system in which the working electrode's potential is precisely regulated using a potentiostat. Platinum working electrodes are utilized for positive potentials, while mercury pool electrodes are favored for extremely negative potentials. The platinum counter electrode is separated from the analyte using a membrane or salt bridge to avoid interference in the analysis.
The chosen potential ensures 100% current efficiency by enabling quantitative oxidation or reduction of the analyte without interference from other sample components. However, water decomposition can become a competing process with high potential. The analysis is carried out by recording the electrolysis current and integrating it over time, determining the charge and analyte amount based on Faraday's law.
To prevent inaccuracies due to prolonged electrolysis times, use electrodes with large surface areas, small-volume electrochemical cells, and rapid stirring to decrease the electrolysis duration.
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