The document describes methods for determining the iodine value of oils, which is a measure of the degree of unsaturation and can be used to classify oils, detect adulteration, and indicate the nature of adulteration. The iodine value is determined by reacting a sample of oil with iodine, then titrating the unreacted iodine with a standard solution, and the number of milligrams of iodine absorbed by 1 gram of oil is a measure of its iodine value. The document provides detailed instructions for determining the iodine value of an olive oil sample through titration.
2. 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
unknownfatoroilbelongs.
3. Have very high iodine number, usually
above 120, since they contain a large
proportionofunsaturatedfattyacids.
Linseedoil,fishoilsandcod-liveroil
Have relatively low iodine number,
below 100.
Olive oil and almond oil
4. Have intermediate iodine values,
which is between 100- 120.
Cottonseed oil and sesame oil
Iodine number & saponification Value
Serves as a means of detecting adulteration
and it also indicates the nature of the adulteration.
6. Objective: 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
7. 1. Introduce about 200mg of the olive oil,
accuratelyweighed,intoa250-mlIodineflask.
Add 20ml of Carbon Tetrachloride and, after
the oil has dissolved, and 25.0ml of Iodochloride
TS,accuratelymeasuredfromaburetorapipet.
Stopper the vessel securely, shake
occasionally, and allow it to stand at 25 ± 5 ˚C for
30minprotectedfromlight.
8. 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
9. Example:
• Determine the Iodine value of a
sample of olive oil weighing
0.2100g if 24.15ml and 12.00ml of
0.1100N Sodium Thiosulfate
solution are required for the blank
and residual titrations,
respectively.
10. 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 𝑥 0.1269
𝑔
𝑚𝑒𝑞
𝑥 100
0.2100𝑔
= 80.8
11. 1. Determine the number of milliliters of exactly 0.1N iodine
absorbed by the sample.
24.15 𝑚𝑙 𝑥 0.1100𝑁
0.1000𝑁
= 25.57 𝑚𝑙 of Na2S2O3 (also iodine) blank titration
12.00𝑚𝑙 𝑥 0.1100𝑁
0.1000𝑁
= 13.20𝑚𝑙 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
0.1697𝑔 𝑥 100
0.2100𝑔
= 80.8
12. 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
13. 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?
