Iodine value

The Iodine Value (IV ) is a fat index for characterizing fats and oils. It is a measure of the content of a fat to unsaturated compounds - in more detail: unsaturated fatty acid moieties in the glycerides. It is the amount in grams of iodine that can be added to 100 g of formal fat. The more olefinic double bonds are in a fat, the more iodine may be added, and is formally the higher the iodine value therefore. In addition, other olefinic impurities such as sterols are recognized. The method can be used for the identification and quality control. It classifies lipids based on their degree of saturation, as this decisive for the aging ( "drying" ) during storage is.

Upon heating of fats (eg frying ) the iodine value decreases.

Methods

Huebl

The iodine value was introduced by Huebl, the fats titrated in the presence of mercuric chloride with iodine, but the actual reagent ( probably iodine chloride ) is formed from mercuric chloride and iodine in situ. Pure iodine does not migrate in fact to alkenes to why the still valid definition of the iodine value is a formal only.

Wijs

The Iodzahlbestimmung according to Wijs according to DIN 53241-1:1995-05. It is based on the addition of iodine monochloride to the olefinic double bond.

The sample is dissolved in chloroform (or other organic solvent, for example cyclohexane) and then mixed in excess with a solution of iodine according to the Wijs. The Wijs iodine solution by an organic solvent, pure acetic acid (glacial), elemental iodine and iodine trichloride. Iodine and iodine trichloride sit in the solution completely iodine monochloride to.

It is important that the iodine solution is anhydrous, as iodine monochloride decomposes in water into hydrogen chloride, iodine and iodic acid. To the formation of Iodradikalen and thus possible distortion of results the sample is kept in the dark after addition of the iodine solution. Results in an electrophilic addition reaction of iodine monochloride to the double bond.

Subsequently, the remaining iodine monochloride is reacted with potassium iodide.

The iodine formed is titrated with sodium thiosulfate and starch as indicator.

Merchant

( Bromination of the double bonds in the dark, reducing the excess bromine with iodide and back-titration of the iodine with thiosulfate )

In the determination of the iodine value according to HP Kaufmann the fat is treated with an excess of bromine. Here, bromine is added to the double bonds in unsaturated fats. This reaction must be carried out in the dark since the formation of bromine radicals is thus suppressed by light. This would lead to undesirable side reactions, and so corrupting to a result increased consumption of bromine.

Then the unused bromine with iodide is reduced to bromide.

Now the amount of the iodine formed is determined by titration with sodium thiosulfate solution.