Estimation of iodine value

Determinant of double bond in fat by Titration method

1. Estimation of Iodine Value Jasmine Juliet .R Teaching Assistant Biotechnology Dept AC&RI, Madurai.

2. Determination Of Iodine Value Of Fats And Oil - Introduction Natural fats and oils are triglycerides . Triglycerides are formed from three fatty acids which are linked to glycerol by fatty acyl esters. Fatty acids are long aliphatic chains with carboxyl groups. These are grouped into saturated or unsaturated based on the number of double bonds present in fatty acid. Unsaturated fatty acids consist of single bonds as well as double bonds and tend to be liquids at room temperature. Naturally occurring unsaturated fats contain double bonds in the cis form .

3. Determination Of Iodine Value Of Fats And Oil - Introduction Hydrogenation leads to the conversion of unsaturated fatty acids to saturated fatty acids. The fatty acids combine with oxygen or halogens depending upon the extent of unsaturation to form saturated fatty acids. So , it is significant to know the degree of unsaturation . There are different methods to know the level of unsaturation in fatty acids, one among them is by determining the iodine number of fats.

4. What is iodine value? Iodine value, also called iodine number or iodine index, is the mass of iodine in grams absorbed by 100 grams of oil/fat. It is used in the estimation of the degree of unsaturation in fatty acids. The double bonds present in unsaturated fatty acids react with the iodine;  the more the iodine number, the more the number of C=C bonds.

5. Principle The oil/fat sample taken in carbon tetrachloride is reacted with an excess of iodine monochloride solution ( Wjis solution). Unsaturated fatty acids undergo halogenation reaction resulting in the addition of an iodine atom to one carbon of the double bond. On completion of the reaction, the remaining iodine monochloride reacts with potassium iodide leading to the formation of molecular iodine. The liberated iodine is then evaluated by titration with a standard solution of sodium thiosulphate .

6. Materials Required Apparatus: Reaction flasks: Standard 250 ml iodine flasks, Erlenmeyer flask, 500 ml capacity. Reagents: 1) Carbon tetrochloride , Hydrochloric acid. 2 ) Iodine solution: 6.5g of Iodine was dissolved in 50ml of Glacial Acetic Acid. 3) Potassium Iodide, 10 % – Dissolve 10 g of KI in 100ml purified water, 4) Potassium dichromate. 5) Sodium Thiosulphate solution, 0.1 N – Standard 6) Starch Indicator solution, 1 %.

7. Erlenmeyer flasks 

8. Procedure – Titration I The prepared sodium thio sulphate solution was standardized by taking 10ml of 10% potassium Iodide solution. Then added 10ml of potassium dichromate (0.1N). Then Added 5ml of 2N Hcl diluted to 100ml with water. Then titrated with thiosulphate until a pale yellow colour appeared . Then 1 ml of starch solution was added the blue colour was produced. Then titrated with thiosulphate until the disappearance of blue colour .. The titration was repeated to get the concordant value from the titrated value.

9. Procedure – Titration I From Titration I, we find out the normality (strength) of Sodium thiosulphate solution by using the following formula: V1N1 = V2N2 Here, V1 = Volume of Potassium dichromate N1 = Normality of Potassium dichromate V2 = Volume of Sodium thiosulphate N2 = Normality of Sodium thiosulphate

10. Procedure – Titration II 0.2g of Oil/fat was weighed and dissolved in 10ml of Carbon tetra chloride . Then the flask was rotated gently to mix the content thoroughly. The flask was kept aside for about half an hour . Then 20 ml of 10% Potassium iodide solution was diluted by adding 200ml of water. The mixture was titrated with standard thio sulphate solution using starch as an indicator. A blank determination was carried out without the oil then Iodine number was calculated .

11. Calculation Iodine value = 12.69 (B – S) N/W Where, B = volume in ml of standard sodium thiosulphate solution required for the blank. S = volume in ml of standard sodium thiosulphate solution required for the sample . N = Normality of the standard sodium thiosulphate solution (Calculated from the Titration I). W = weight in g of the sample.

12. Uses of estimation of Iodine value The iodine value is a measure of the relative degree of unsaturation in oil components, as determined by the uptake of  halogen . Because the melting point and oxidative stability are related to the degree of unsaturation , IV provides an estimation of these quality factors. The greater the iodine value, the more unsaturation and the higher the susceptibility to  o xidation .  Peanut oil  (IV 82–107) is more saturated than corn (IV 103–128), cottonseed (IV 99–113), or  linseed  (IV 155–205) oils; However, it is considerably less saturated than coconut (IV 7.7–10.5), palm (IV 44–54) or butter (IV 25–42) oils.