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Determination of peroxide value of oils and fats


The peroxide value is a measure of the peroxides contained in a sample of fat, expressed as milli-equivalents of peroxide per kg of the material.


The material in an acetic acid-chloroform medium is treated with an aqueous solution of potassium iodide. The liberated iodine is titrated with a standard sodium thiosulphate solution.



Pipette – Graduated, 1 ml capacity.
Conical flask – Glass-stoppered, 250 ml capacity.


Acetic Acid-Chloroform Solution – Mix three parts by volume of glacial acetic acid, with 2 parts by volume of chloroform.
KI Solution – Saturated. Prepare a saturated solution of potassium iodide in recently boiled distilled water. Store in the dark.
Na2S2O3 Solution – 0.1 N, accurately standardized.
Na2S2O3 Solution – 0.01 N. This solution is prepared by diluting 100 ml of an accurately standardized solution of 0.1 N Na2S2O3 to 1 liter with freshly boiled and cooled distilled water.
Starch Solution – 1 % by mass


  • Weigh 5.00 ± 0.05 g of sample of fat in a 250 ml glass stoppered conical flask and then add 30 ml of the acetic acid-chloroform solution.
  • Swirl the flask until the sample is dissolved.
  • Add 0.5 ml of saturated potassium iodide solution.
  • Allow the solution to stand exactly one minute with occasional shaking and then add 30 ml of distilled water.
  • Titrate with 0.1 N sodium thiosulphate solution with constant and vigorous shaking.
  • Continue titration until the yellow color almost disappears, Add 0.5 ml of starch solution and continue titration till the blue color just disappears.
  • If the titer value is less than 0.5 ml, repeat the determination using 0.01 N Na2 S2 O3 solution.
  • Conduct a blank determination of the reagents in the same way.
  • The titration in blank determination should not exceed 0.1 ml of the 0.1 N Na2 S2 O3 solution.



S = Volume, in ml, of Na2S2O3 solution used up by the sample,

B = Volume, in ml, of Na2S2O3 solution used in the blank,

N = Normality of Na2S2O3 solution, and W = weight, in g, of the sample taken.


The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst (repeatability) shall not exceed 0.1 meq/kg.

The peroxide value of fresh edible oils is usually within 10 meq/kg.


• Standard solutions used should be properly standardized.
• Maintain dark conditions during the experimentation that should be properly maintained.

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