VeritasC&E
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Simple & Easy Easy Way to Determine PUFA Content in Oils?
What is a quick/simple and easy way to determine the polyunsaturated fat content (proportion) in vegetable oils samples?
[Edited on 30-12-2022 by VeritasC&E]
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Bedlasky
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Iodometric titration. Usually IBr is used instead of I2 due to better reactivity, but iodine still do the job. Add excess of I2 of known concentration
(4 decimal places) to the flask with fat dissolved in chloroform, let it react for 30 minutes in stoppered flask in the dark, then titrate leftover I2
with thiosulfate of known concentration until purple coloration of CHCl3 disappears. If you will use IBr, add KI solution before titration with
thiosulfate (IBr + I- --> I2 + Br-). Thiosulfate can be standardized with potassium dichromate, iodate or bromate, then it can be used for I2
standardization (or you can use pure ascorbic acid).
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VeritasC&E
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Quote: Originally posted by Bedlasky  | | Iodometric titration. Usually IBr is used instead of I2 due to better reactivity, but iodine still do the job. Add excess of I2 of known concentration
(4 decimal places) to the flask with fat dissolved in chloroform, let it react for 30 minutes in stoppered flask in the dark, then titrate leftover I2
with thiosulfate of known concentration until purple coloration of CHCl3 disappears. If you will use IBr, add KI solution before titration with
thiosulfate (IBr + I- --> I2 + Br-). Thiosulfate can be standardized with potassium dichromate, iodate or bromate, then it can be used for I2
standardization (or you can use pure ascorbic acid). |
Thank you!!
Is it possible to use ethyl ether as a solvent?
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Bedlasky
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Yes you can use ether. The point is that fat and iodine are well soluble in the solvent. When using Et2O, I would probably add some water and starch
as a indicator before thiosulfate titration. I don't know how precise is end point without starch in Et2O, never tried it. Chlorinated solvents give
nice end point with that disappearence of purple coloration. But yellow colour is less distinctive than purple so it may give you slightly lower
volume at the end point. Starch offers very sharp end point because of its very distinctive blue colour.
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VeritasC&E
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| Quote: Originally posted by Bedlasky | | Yes you can use ether. The point is that fat and iodine are well soluble in the solvent. When using Et2O, I would probably add some water and starch
as a indicator before thiosulfate titration. I don't know how precise is end point without starch in Et2O, never tried it. Chlorinated solvents give
nice end point with that disappearence of purple coloration. But yellow colour is less distinctive than purple so it may give you slightly lower
volume at the end point. Starch offers very sharp end point because of its very distinctive blue colour. |
Thank you! You're awesome : )
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Fery
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26th ICHO
Practical problems
Problem I
3) Determination of the Iodine Number
page 563
https://www.iuventa.sk/files/documents/5_icho/past%20competi...
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