Page 108 - Feed Lab

Suguna Management System Ver 1.0 / SOP / FQL / P2 - 24 Page 1 of 2

24. Estimation of Iodine Value

PRINCIPLE PROCEDURE
Fat or oil is mixed with iodine monochloride solution to FMelt test sample, if not already liquid (do not
o
halogenate double bonds in fat or oil. Excess iodine exceed sample melting point by > 10 C). Pass test
monochloride is reduced to free iodine in presence of sample through double layer of filter paper to
potassium iodide, and free iodine is measured by remove any solid impurities and traces of water.
titration with sodium thio sulphate using starch as Test sample must be absolutely dry. Let filtered test
0
0
indicator. sample cooled to 68 C - 71 C. (Picture - 1)
FImmediately weigh amount of test sample as
REAGENTS
indicated in table according to the expected Iodine
FWijs solution: 16.5gm of Iodine Monochloride (ICl) value, in a clean dry 500ml flask. Prepare at least
in a one litre volumetric flask with Glacial acetic two blank determinations to run with each sample
acid.
group. Add 15ml Cyclohexane- acetic acid solvent
FPotassium Iodide: 15gm potassium iodide in to each test sample and swirl to ensure that it is
100ml of distilled water. completely dissolved. ( Picture - 2)

FStarch Solution: 1gm of starch in 100ml of distilled FDispense 25ml Wijis solution into flask containing
water. test sample, stopper the flask and swirl to mix.
Immediately set time for 1.0 hour and store flasks in
FSodium thio sulphate 0.1M: 2.5 gm of Sodium dark at 25 C - 30 C for duration of reaction.
0
0
thio sulphate in 100ml of distilled water. (Picture - 3)
FRemove flasks from dark, add 20ml potassium
Standardization of Sodium thio sulphate
Accurately weigh 0.16 - 0.22 g dried, finely ground iodide solution, and mix. Add 150 ml water and
K Cr O to nearest 0.0001g into 250ml conical flask, gradually titrate with 0.1M sodium thio sulphate
2
2
7
dissolve in 25ml water, add 5 ml Hydrochloric acid and solution with constant and vigorous shaking.()
20ml potassium iodide and rotate to mix. Let stand for 5 (Picture - 4)
minutes. Add 100ml water. Titrate with sodium thio
sulphate solution, shaking continuously until yellow FContinue titrating until yellow colour has almost
colour has almost disappeared. Add 1-2ml starch disappeared. Add 1-2ml starch indicator solution
indicator solutions, and continue adding thio sulphate to flasks and continue titrating until blue colour has
solution until blue colour just disappears. just disappeared. (Picture - 5)

Prepared by : Approved by :
96 Director - Technical