Overview
ISO 1242:2023 - Essential oils: Determination of acid value by two titration methods, manual and automatic specifies two validated titration procedures for measuring the acid value of essential oils. The methods are based on neutralization of free acids with a titrated ethanolic potassium hydroxide (KOH) solution and are suitable for routine quality control and laboratory analysis. Note: these methods are not applicable to essential oils containing appreciable amounts of lactones (for example, Massoïa essential oil).
Key topics and requirements
- Principle: Neutralization of free acids using an ethanolic KOH solution; end-point detected by coloured indicator (manual) or pH/curve analysis (automatic).
- Reagents: Ethanol 96% (freshly neutralized), standard ethanolic KOH (examples: 0.05, 0.10, 0.50 mol·L−1), and appropriate indicators (phenolphthalein/thymolphthalein or phenol red for phenolic oils).
- Apparatus:
- Manual: Class A burette (2 ml or 5 ml, 0.01 ml graduations), measuring cylinder, analytical balance (0.001 g).
- Automatic: Titrator with software and same-precision balance.
- Sampling & preparation: Prepare samples per ISO 356; ensure representative, undamaged samples.
- Procedure:
- Manual titration: weigh optimal test portion, add neutralized ethanol and indicator, titrate to persistent colour change (30 s).
- Automatic titration: weigh sample in titration cup, add ethanol, run titration and review titration curve/equivalence point suggested by software.
- Calculation: Acid value A (mg KOH/g) = 56.11 × C × V / m, where C = KOH concentration (mol·L−1), V = volume KOH used (mL), m = mass of test portion (g).
- Precision: Repeatability ≤ 0.05 absolute or 2.5% relative; reproducibility ≤ 0.10 absolute or 5% relative.
- Reporting: Include sample ID, ISO 1242:2023 reference, method used, results, deviations, unusual features, and date.
Applications
- Quality control for essential oil producers, perfumers, cosmetics and aromatherapy manufacturers.
- Analytical and testing laboratories verifying product specifications and shelf stability.
- Regulatory and customs laboratories checking compliance with product standards.
- R&D teams comparing acid hydrolysis, degradation, or storage effects on essential oils.
Who should use this standard
- Laboratory analysts and chemists performing essential oil titrations.
- Quality assurance managers in fragrance, cosmetic, and botanical industries.
- Certification bodies and accreditation laboratories seeking reproducible methods for acid value determination.
Related standards
- ISO 356 - Preparation of test samples (essential oils)
- ISO 385 - Laboratory glassware - Burettes
- ISO 709 - Determination of ester value
- ISO 212 - Sampling of essential oils
Using ISO 1242:2023 helps ensure consistent, traceable acid value measurements for essential oils, improving comparability across labs and supporting product quality and regulatory compliance.
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