Overview
EN ISO 3961:2025 (ISO 3961:2024) specifies the reference volumetric method for determining the iodine value (IV) of animal and vegetable fats and oils. The iodine value is expressed as grams of iodine absorbed per 100 g of fat and is a key indicator of the degree of unsaturation. The standard updates and supersedes EN ISO 3961:2018 and includes a calculation procedure in Annex B for deriving IV from fatty‑acid composition (not applicable to fish oils).
Key topics and technical requirements
- Principle: Reaction of unsaturated bonds with Wijs reagent (iodine monochloride in acetic acid), quench with potassium iodide and water, and titration of liberated iodine with sodium thiosulfate.
- Reference reagents and solutions: Wijs reagent (I/Cl ratio 1,10 ± 0,1), sodium thiosulfate standard solution (0.1 mol/L), potassium iodide, starch indicator, and a cyclohexane–glacial acetic acid solvent mixture.
- Apparatus: Analytical balance (readability 0.0001 g or 0.0005 g as required), 500 mL conical flasks, class A pipettes and burettes (or autotitrator), volumetric flasks per ISO 1042.
- Sample preparation and test portion: Follow ISO 661 for test sample prep; Table 1 in the standard gives initial test‑portion masses and solvent volumes to ensure appropriate excess of reagent.
- Annex B (calculated IV): Method to compute IV from fatty‑acid composition (based on AOCS Cd 1c‑85). Not applicable to fish oils; results can differ from the volumetric method for cold‑pressed, crude/unrefined, or (partially) hydrogenated oils because of impurities and thermal degradation products.
- Safety and quality controls: Wijs reagent is hazardous - use fume hood and follow safety regulations. Standardization of sodium thiosulfate and controls for reagent shelf life required.
- Precision and reporting: Document includes repeatability and reproducibility data from interlaboratory studies and specifies required details for test reports.
Applications and users
- Who uses it: Analytical and quality‑control laboratories, edible oil processors, oilseed producers, regulatory bodies, research institutions, and certification bodies.
- Practical uses:
- Quality control of vegetable and animal fats and oils (degree of unsaturation).
- Specification compliance for food, feed and oleochemical industries.
- Verification of product labeling and tracking changes after processing (hydrogenation, refining).
- Comparative analysis where calculated IV from fatty‑acid profiles is needed (with caveats).
Related standards
- ISO 661 - Preparation of test sample
- ISO 5555 - Sampling of fats and oils (recommended)
- AOCS Official method Cd 1c‑85 - Basis for Annex B calculation
Keywords: iodine value, IV, EN ISO 3961:2025, ISO 3961:2024, Wijs reagent, fats and oils analysis, fatty acid composition, reference method, laboratory testing.
