ISO 3961:2018

Overview

ISO 3961:2018 specifies a reference method for determining the iodine value (IV) of animal and vegetable fats and oils. The standard defines the volumetric (Wijs) titration procedure as the reference method and includes an informative Annex B that describes how to calculate IV from fatty acid composition (based on AOCS Cd 1c‑85). Annex B is not applicable to fish oils and can give different results for cold‑pressed, crude/unrefined, or partially hydrogenated oils because calculated IV is affected by impurities and thermal degradation products.

Keywords: ISO 3961:2018, iodine value, IV determination, Wijs reagent, fatty acid composition.

Key topics

• Scope and applicability
  • Reference method for IV of animal and vegetable fats and oils.
  • Annex B: calculated IV from fatty acid data (not for fish oils).
• Principle
  • Reaction of unsaturated bonds with Wijs reagent (iodine monochloride in acetic acid), liberation of iodine, and titration with standardized sodium thiosulfate.
• Reagents and safety
  • Use analytical grade reagents; Wijs reagent is corrosive and toxic - use a fume hood and appropriate PPE.
  • Key reagents: Wijs reagent, cyclohexane/acetic acid solvent, KI solution, starch indicator, standardized Na2S2O3, water.
• Apparatus and sampling
  • Standard lab glassware, analytical balance, pipettes, burettes or autotitrators.
  • Sampling is covered by ISO 5555 (recommended); sample preparation by ISO 661.
• Procedure and calculation
  • Reaction time: typically 1 h (IV