SOP: Peroxide Value of Essential Oils

GIFSQ — Global Institute for Food Safety & Quality

Principle

Peroxides in the oil oxidize iodide to iodine in an acetic acid–chloroform solvent; the liberated iodine is titrated with standard sodium thiosulphate, giving the peroxide value as millimoles of peroxide per litre.

Reagents

a. Saturated potassium iodide solution in water — prepare fresh.

b. Solvent mixture: mix 3 volumes of glacial acetic acid and 2 volumes of chloroform.

c. 0.1 N sodium thiosulphate solution.

d. Starch indicator or thyodene.

Procedure

To 10 ml of sample, add 50 ml of solvent mixture and 1.0 ml of saturated potassium iodide solution

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Let stand for exactly 1 min with gentle shaking

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Add 100 ml of distilled water, and starch indicator or thyodene

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Titrate immediately with 0.1 N sodium thiosulphate solution

Calculation

Peroxide value, millimoles of peroxide/litre = ml of 0.1 N Na₂S₂O₃ × 5

Peroxide value may also be calculated as milliequivalents of peroxide per 100 g of sample; values so calculated will be approximately twice those calculated by this method.

Where,

• ml of 0.1 N Na₂S₂O₃ = volume of 0.1 N sodium thiosulphate solution used in the titration

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

EOA Specifications and Standards, Essential Oil Association of USA, Inc., Determinations 1-T.