IODINE VALUEThe number of grams of iodine absorbed under specified conditions by 100 g of oil, fat, wax, or other substances.A quantitative measure of the proportion of unsaturated fatty acids present, both free and combined as esters, that have the property of absorbing iodine.

Determination of Iodine Number of Fats and Oils

Serves to characterize them and to indicate whether they are pure or admixtures.Used to indicate in a definite manner the class to which an unknown fat or oil belongs.

Drying OilsHave very high iodine number, usually above 120, since they contain a large proportion of unsaturated fatty acids. Linseed oil, fish oils and cod-

liver oilNondrying OilsHave relatively low iodine number, below 100.Olive oil and almond oil

Have intermediate iodine values, which is between 100- 120.Cottonseed oil and sesame oil

Semidrying Oils

Iodine number & saponification ValueServes as a means of detecting adulteration

and it also indicates the nature of the adulteration.

Required solutions:• Iodochloride TS, • Potassium Iodite Test Solution• 0.1 N Sodium Thiosulfate

Solution• Starch Test

METHODS FOR THE DETERMINATION

OF THE IODINE NUMBERHübl, Hanus, and Wijs Methods

Exercise 13.3Objective: To determine the Iodine Value of Olive Oil.Materials required:• About 1g of Olive Oil• 50ml of Carbon Tetrachloride• 60ml of Iodochloride TS• 50ml of Potassium Iodide TS• About 100ml of 0.1N Standardized

Sodium Thiosulfate Solution

Procedure:1. Introduce about 200mg of the olive oil,

accurately weighed, into a 250-ml Iodine flask.

Add 20ml of Carbon Tetrachloride and, after the oil has dissolved, and 25.0ml of Iodochloride TS, accurately measured from a buret or a pipet.

Stopper the vessel securely, shake occasionally, and allow it to stand at 25 ± 5 ˚C for 30 min protected from light.

2. Then add 20ml of Potassium Iodide TS and 100ml of recently boiled and cooled water, and titrate the liberated iodine with 0.1N Sodium Thiosulfate, shaking thoroughly after each addition of thiosulfate. When the iodine color becomes quite pale, add 1ml of Starch TS and continue the titration with thiosulfate until the blue color is discharged.

3. Carry out a blank test at the same time with the same quantities of the same reagents and in the same manner and titrating as directed.

Example:• Determine the Iodine value of a

sample of ol ive oil weighing 0.2100g if 24.15ml and 12.00ml of 0.1100N Sodium Thiosulfate solution are required for the blank and residual t itrations, respectively.

Calculation of the Iodine Value

Solution:1. Determine the number of

milliequivalents of halogen calculated as iodine consumed by the sample.

2. Multiply 1.337meq of iodine by 0.1269g, the weight of 1 meq of iodine.

3. Divide the sample weight into the grams of iodine in order to determine the grams of iodine consumed by exactly 1g of oil. Multiply this value by 100 to obtain the iodine number.

(24.15𝑚𝑙−12.00𝑚𝑙 )𝑥 0.1100𝑁 𝑥0.1269 𝑔𝑚𝑒𝑞 𝑥100

0.2100𝑔 =80.8

1. Determine the number of milliliters of exactly 0.1N iodine absorbed by the sample.

of Na2S2O3 (also iodine) blank titration

of Na2S2O3 (also iodine) residual titration

26.57ml – 13.20ml = 13.37ml consumed by the oil sample

2. Multiply 13.37ml x 0.01269g, the number of grams of iodine present in 1.00ml of exactly 0.1N iodine solution.

13.37 ml x 0.01269g = 0.1697g of Iodine

ALTERNATIVE SOLUTION

1.Define the term iodine value.2.Indicate by structural

formulas how iodine may add on to an unsaturated fatty acid.

3.How many determination of the iodine number be used to supplement the information relative to the nature and purity of oil gained through a determination of the saponification value.

QUESTIONS AND PROBLEMS

4. What functions do iodochloride, acetic acid, carbon tetrachloride and potassium iodide serve in the determination of the iodine number of the oil?

5. Give an unknown sample of fatty oil, what observations, tests and determinations would you perform in order to establish the identity and purity of the oil?