starch is used as the indicator in the determination of peroxide value in oil. when titrating against sodium thiosulphate the blue black colour is supposed to disappear.
Maybe there is no peroxide present?
Do You see the color change to brown when potassium iodide is added? This is caused by the formation of iodine (I2) which afterward is titrated with thiosulfate using starch as an indicator.
If not, the reaction conditions could be wrong. If I remember right, the the iodine-peroxide reaction should be performed in an acidic media.
Hi Mongare
It sounds a little odd. The change in color when iodide is added indicates that at least some of it is oxidized and addition of starch should then make it dark.
Maybe it is the test-conditions. Which standard method do you follow? AOCS Official Method Cd 8b-90 is widely used, but there are many others.
These links may give some inspiration:
https://daim.idi.ntnu.no/masteroppgaver/006/6956/masteroppgave.pdf
Article Redox potentiometric determination of peroxide value in edib...
Dear Nyaboke,
I have the same problem when I add KI I get yellow color and when add starch indicator I have white color not blue or black color,
Do you have a way to solve this problem
Interesting question, I hope to benefit from the scientific comments .
With appreciation
Adding KI and following its oxidation to iodine by H2O2 and titration against sodium thiosulphate using starch indicator as shown in
http://www.h2o2.com/technical-library/analytical-methods/default.aspx?pid=70&name=Iodometric-Titration
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