Overview - ISO 18321:2015 (Peroxide value in essential oils)
ISO 18321:2015 specifies an analytical method for the determination of the peroxide value in an essential oil. The peroxide value is a quantitative indicator of the oxidation present in an oil and is widely used in quality control to assess rancidity, storage stability and product acceptability. The method is an iodometric redox titration and can be performed by conventional volumetric titration or by potentiometric titration (recommended for highly coloured essential oils).
Key topics and technical requirements
- Principle: Iodide is oxidized by peroxides to release iodine, which is titrated with sodium thiosulfate (iodometry). End point can be detected visually with starch indicator or potentiometrically.
- Reagents and quality: Analytical-grade reagents and Grade 3 water (ISO 3696). Typical reagents include trichloromethane (chloroform) or cyclohexane, glacial acetic acid, saturated potassium iodide, and 0.01 N or 0.1 N sodium thiosulfate.
- Apparatus: Standard laboratory glassware (balance ±1 mg, 250 ml Erlenmeyer, shaker, pipettes, 10 ml burette) and optionally a potentiometer for automated titration.
- Sampling and preparation: Sampling and test-sample preparation are referenced to ISO 212 and ISO 356. Samples should be homogenized without heating/airation, tested immediately, and filtered if impurities are visible.
- Procedure: Typical test portion is 10 ml essential oil; add solvent, acetic acid and KI, shake, dilute with water, and titrate. Use 0.1 N thiosulfate when peroxide values are expected >20 mmol/l, 0.01 N for lower values. Perform a blank titration.
- Automated titration notes: Use amber autosampler vessels to prevent iodine formation; if automating KI addition, use a 70% KI solution in opaque bottles and adjust added volume.
- Results and calculation: Peroxide value is calculated from the difference between test and blank titrant volumes and titrant normality. Conversion from mmol/l to meq/kg uses a density-based factor.
- Precision: Repeatability: differences not exceeding 5% (absolute) or 0.1 (relative). Reproducibility: differences not exceeding 10% (absolute) or 0.3 (relative).
Applications and users
ISO 18321:2015 is used by:
- Quality control laboratories in the fragrance, flavor and aromatherapy industries
- Essential-oil producers and packers monitoring oxidation and shelf life
- Regulatory and testing laboratories verifying product conformity
- Analytical chemists developing stability and storage studies
Practical uses include routine peroxide monitoring, batch release testing, stability testing and comparative quality assessment.
Related standards
- ISO 212 - Essential oils: Sampling
- ISO 356 - Essential oils: Preparation of test samples
- ISO 3696 - Water for analytical laboratory use (Grade 3)
- (Referenced glassware standard) ISO 385
Keywords: ISO 18321:2015, peroxide value, essential oils, iodometry, potentiometric titration, oxidation testing, peroxide determination, quality control.
