Water content

Cards (11)

  • 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