Karl Fischer (March 24, 1901 – April 16, 1958) was a German chemist
Published a method in 1935 to determine trace amounts of water in samples. This method is now called Karl Fischer titration. Abbreviations: KF or KFT
It remains the primary method of water content determination used worldwide by:– Government – Food Science– Academia – Research– Industry – Quality Control
Two Types of Karl Fischer Titration
Volumetric– Iodine is added mechanically to a solvent containing the sample– Water is quantified from the volume of KF reagent consumed– 100 to 1×10⁶ ppm (0.01 – 100%)
Coulometric– Iodine is generated electrochemically in situ during the titration– Water is quantified from the total charged passedQ = 1 C = 1 A x 1 s where 1 mg H₂O = 10.72 C– 1 to 50,000 ppm (0.0001 – 5%)
Karl Fischer Reaction
Bunsen Reaction:2H₂O + SO₂ + I₂ → H₂SO₄ + 2HIROH + SO₂ + R'N → [R'NH]SO₃R + H₂O + I₂ + 2R'N → 2 [R'NH] I + [R'NH] SO₄R
Once the intermediate alkylsulfite salt is produced, it is oxidized by iodine to the alkylsulfate salt
Oxidation reaction consumes water
pH sensitive: optimal range pH 5 – 8 otherwise buffer highly acidic/basic samples