Iodine value (1)

iodine value

1. DETERMINATION OF IODINE VALUE PRESENTED BY HARISH PUDI M PHARM, 2 nd SEM DEPT OF PHARMA ANALYSIS, PES COLLEGE OF PHARMACY.

2. CONTENTS DEFINITION IMPORTANCE PRINCIPLE METHODS PROCEDURE CALCULATION

3. IODINE VALUE The iodine value of an oil/fat is the number of grams of iodine absorbed by 100g of the oil/fat, when determined by using Wijs solution. Analytical importance The most important application of the iodine value is to determine the amount of unsaturation contained in fatty acids. Iodine number is directly proportional to content of unsaturated fatty acids, and it is used to analyze the degree of adulteration. This unsaturation is in the form of double bonds which react with iodine compounds. The higher the iodine value, the more unsaturated fatty acid bonds are present in a fat.

4. Principle: The oil/fat sample taken in carbon-tetrachloride is treated with a known excess of iodine monochloride solution in glacial acetic ( Wijs solution). The excess of iodine monochloride is treated with potassium iodide and the liberated iodine estimated by titration with sodium thiosulfate solution.

5. Methods for the determination of iodine value Huebl's iodine Wijs iodine value Iodine by H. P. Kaufmann Huebl's iodine Introduced the iodine value was Hübl which titrated fats in the presence of mercuric chloride with iodine, but with the actual reagent (probably iodine chloride) is formed in situ from mercuric chloride and iodine. Pure iodine accumulates concerned not to alkenes, which is why the still valid definition of iodine is only a formal one. Wijs iodine value Addition of  iodine chloride  and back-titration with  sodium thiosulphate  

6. Iodine by H. P. Kaufmann ( Bromination  of the double bonds in the dark, reducing the excess bromine with iodide, back titration of iodine with thiosulfate) The fat is mixed with an excess of bromine. This bromine is added to the double bonds in the unsaturated fats. This reaction must be carried out in the dark, since the formation of bromine radicals is suppressed by light. This would lead to undesirable side reactions, and thus falsifying a result consumption of bromine.

7. Procedure: Expected Iodine Weight to be take for Value estimation (g)

8. Weigh accurately an appropriate quantity of the dry oil/fat. into a 500 ml conical flask with glass stopper, to which 25 ml of carbon tetrachloride have been added. . Mix the content well. Add 50 to 60 percent of Wij’s solution over that actually needed. Pipette 25 ml of Wij's solution and replace the glass stopper after wetting with potassium iodine solution. Swirl for proper mixing and keep the flasks in dark for half an hour for non-drying and semi-drying oils and one hour for drying oils. Carry out a blank simultaneously. After standing, add 15 ml of potassium iodide solution, followed by 100 ml of recently boiled and cooled water, rinsing in the stopper also. PROCEDURE

9. Titrate liberated iodine with standardized sodium thiosulphate solution, using starch as indicator at the end until the blue colour formed disappears after thorough shaking with the stopper on. Conduct blank determinations in the same manner as test sample but without oil/fat. Slight variations in temperature appreciably affect titre of iodine solution as chloroform has a high coefficient of expansion . It is thus necessary that blanks and determinations are made at the same time.

10. 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. W = weight in g of the sample.

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