Water content

• Titrimetric method / Karl Fischer method

  • this method depends upon the fact that a solution of sulfur dioxide and iodine in pyridine and methanol reacts with water quantitatively
  • requires rigid exclusion of atmospheric moisture.
• Colorless soln

  • endpoint of titration may be determined electrometrically or visually by a change from a canary yellow to amber color
• Colored soln

  • endpoint is obscure and is best determined electrometrically
• Method I-A (Direct Titration)

  • Use Karl-Fischer Reagent
• 1ml of KF reagent = 5mg H2O
• Composition of KF Reagent:

  • iodine
  • methanol
  • pyridine
  • sulfur dioxide
• Method I-B (Residual Titration)

  • excess reagent is added to the test specimen, sufficient time is allowed for the reaction to reach completion, and the unconsumed reagent is titrated with a standard solution of water in a solvent such as methanol
  • applicable generally and avoid the difficulties that may be encountered in the direct titration
• Method I-C (Coulometric Titration)

  • KF reaction is used
  • iodine, however, is not added in the form of a volumetric solution but is produced in an iodide containing solution by anodic oxidation.
• Method II (Azeotropic-Toluene Distillation)/ Volumetric Method

  • with the help of toluene moisture apparatus, water may be determined by volume measurement
• Azeotropic

  • a mixture of organic liquids with different boiling temperatures but distilling at a constant temperature
• Method III Gravimetric Method

  • follows the principle of loss on drying