Karl Fischer Titration

Principle of Karl Fischer Titration

The principle of Karl Fischer titration is based on the oxidation reaction between iodine and sulphur dioxide. Water reacts with iodine and sulphur dioxide to form sulphur trioxide and hydrogen iodide. An endpoint is reached when all the water is consumed. The chemical equation for the reaction between sulphur dioxide, iodine, and water (which is employed during Karl Fischer titration) is provided below.

I2 + SO2 + H2O → 2HI + SO3

There are two determination methods different in iodine-providing principle: the volumetric titration method and the coulometric titration method.

There are two determination methods different in iodine-providing principle:

  1. Volumetric titration method and
  2. Coulometric titration method.

In the volumetric titration method, iodine required for reaction with water is previously dissolved in water determination TS, and water content is determined by measuring the amount of iodine consumed as a result of reaction with water in a sample.

In the coulometric titration method, first, iodine is produced by electrolysis of the reagent containing iodide ion, and then, the water content in a sample is determined by measuring the quantity of electricity which is required for the electrolysis (i.e., for the production of iodine), based on the quantitative reaction of the generated iodine with water.

  • Basic ingredients of KF Reagents
    • Iodine – I2
    • Sulfur dioxide – SO2
    • Buffer – Imidazole
    • Solvent – Methanol

Water Equivalency Factor Formula:

Water Equivalency Factor (F) = 0.1566 x W / V

  • Where  W = is the weight in mg of sodium tartarate
  •  V = is the volume in ml of the Karl Fisher reagent required.

% of Water Content by using the formula:

% of Water Content= Volume Display x Water Equivalency factor of KF x 100 / Weight of Sample taken in mg

Water Content in PPM =  % of  Water content x 10000

  • This is a specific method. Only water will be determined. The method is rapid (a few minutes).
  • With KF titration both free and bound water can be determined, e.g. surface water on crystals or the water contained inside them.
  • Why we use sodium tartrate in Karl Fischer?
    • It is stable and non-hygroscopic, under normal conditions.
  • What electrode is KF titration?
    • KF titration technology uses a double platinum electrode.
  • What is difference between LOD and water content?
    • Water content is determined by the Karl Fischer titration method and it consists of only water i.e moisture content. Loss on drying (LOD) is determined by heating the sample below its melting point in an oven and it includes all volatile matter including water content and solvents.

For Operation and Calibration of Karl Fischer Titrator SOP click below link: Operation and Calibration of Karl Fischer Titrator SOP