Module 14: Electrogravimetry and Coulometry

• Electrogravimetry


  oldest electroanalytical technique.
• Working Electrode


  where analytical reaction occur.
• Current


  rate of flow of electric charge.
• Voltage


  difference of electrode potential between 2 points.
• Potential


  difference in energy that drives the flow of charge.
• Potentiostat


  maintains the working electrode potential at a constant value relative to a reference electrode.
• Electrogravimetry without potential control

  potential of the working electrode is uncontrolled.
• Potentiostatic Method


  potential of the working electrode is maintained at a constant level.
• Coulometry


  measurement of the amount of electricity.
• Samples used in Chloride determination

  • Serum
  • Sweat
  • CSF (cerebrospinal fluid)
• Coulometry


  Principles: Measurement of the quantity of electricity used in an electrochemical reaction at constant potential or constant current.
• Coulometry


  Applications: Quantitative determination of many species in solution, especially at trace levels (micrograms or less); relative precision 0.2-5%.
• Coulometry


  Advantages: unstable titrant and easy to automate.
• Coulometric Methods


  involve measuring the quantity of electricity.
• Coulometry


  uses FARADAY’S LAWS OF ELECTROLYSIS.
• Constant Potential


  the current diminishes to zero as the reaction goes to completion.
• Constant Current


  involves generation of titrant.
• Coulometric Titrations


  constant current methods involve the generation of a titrant for a measured length of time, the completion of the reaction with the species to be determined being indicated by any of the methods used in titrimetric analysis.
• Constant-current sources, often just a battery, should be capable of delivering currents of 10-100 mA with an accuracy of 0.5% or better.
• Pre-titration method


  to eliminate errors due to impurities in reagents used in the preparation of the sample.
• Coulometric Titrations


  Applications: the coulometric generation of titrants is widely applicable to redox, precipitation, acid-base and complexing reactions. Of particular value is the determination of many organic compounds with bromine and of mercaptans and halides. Relative precision of 0.2-5%.