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Iodine number in biodiesel

The iodine number is a measure for the number of double bonds in a sample.

It is the amount of iodine (in g/100 g sample) that can be added to the sample under the given conditions.

The determination of the iodine number in fatty acids or biodiesel is covered by European standard EN 14111.

An aliquot of the fatty acid or biodiesel sample is dissolved in a mixture of cyclohexane and glacial acetic acid and treated with Wijs reagent.

After a defined time has elapsed, potassium iodide and water are added. The released elemental iodine is then titrated with sodium thiosulfate solution. EN 14111 allows both optical (with starch solution as the indicator) and potentiometric endpoint determination.