Iodine Value and the Test Method - Carboxyl / Alfa Chemistry

Iodine value

An indicator of unsaturated degree in an orgnic compound
Mainly used for the determination of oil, fatty acid, wax and polyester.
The higher the unsaturated degree, the higher the iodine value.
The iodine value of dry oil is greater than that of non-dry oil.

Test Method

Commonly used method

Rapid titration method

Wijs

Hanus

Hubl

Mercury acetate was used as accelerant
Kaufman rapid method
Bromine chloride method

Introduction to the most commonly used Wijs method

The sample is dissolved in chloroform.
Treated with excess iodine chloride (ICl) glacial acetic acid solution, some halogens react with double bonds in unsaturated fats, while others remain.
Saturated potassium iodide solution (KI) is added to the mixture and reacts with the remaining free ICl to form potassium chloride (KCl) and diiodide (I₂).
In the presence of starch, the release of I2 was titrated with sodium thiosulfate to indirectly determine the concentration of iodine in the reaction.

Fig. 1 Main reaction equations of Wijs method

IV (g I/ 100 g) can be calculated by:

IV (g I/ 100 g)

V₁ - the volume f sodium thiosulphate required to titrate the blank solution
V₂ - the volume of sodium thiosulphate required to titrate the test solution that contained either solid fat or oil as the sample
N - the normality of sodium thiosulfate solution in Eq/ L
12.69 - the conversion factor from mEq sodium thiosulfate to grams of iodine
M - the weight of the sample in grams

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The chemists at Alfa Chemistry have extensive experience in the testing of chemical substances. Alfa Chemistry strictly follows the standard of iodine measurement, providing you with iodine measurement of various chemicals. Please feel free to contact us for more details.