ISO 3961:2024

Overview

ISO 3961:2024 - "Animal and vegetable fats and oils - Determination of iodine value" specifies the reference (volumetric) method for measuring the iodine value (IV) of animal and vegetable fats and oils. The seventh edition (2024) updates the established Wijs-method procedure and includes an informative Annex B that describes a calculation method for IV from fatty acid composition (not applicable to fish oils). The standard is the accepted laboratory method for reporting IV as grams of iodine absorbed per 100 g of fat.

Key topics and requirements

• Scope: Reference volumetric method for IV of animal and vegetable fats and oils; Annex B covers calculated IV from fatty acid data (excludes fish oils).
• Principle: Dissolve sample in cyclohexane/acetic acid solvent, react with Wijs reagent (iodine monochloride), quench with potassium iodide and water, then titrate liberated iodine with standardized sodium thiosulfate.
• Reagents & safety: Lists required reagents (Wijs reagent, KI, starch indicator, Na2S2O3, solvent, water). Wijs reagent is corrosive and volatile - use a fume hood and appropriate PPE.
• Apparatus: Analytical balance, 500 ml conical flasks, pipettes, burettes or autotitrator, volumetric flasks per ISO recommendations.
• Procedure specifics: Test-portion mass selection (Table 1), reaction times (typically 1 h for IV <150, 2 h for IV >150 or problematic matrices), blank determination, titration end point (starch indicator or potentiometric).
• Calculation: IV calculated from titration volumes and thiosulfate concentration using the standard formula; results rounded per table (≤60 → 0.1 g/100 g; >60 → 1 g/100 g).
• Precision: Repeatability and reproducibility defined; precision statistics derived from interlaboratory studies (detailed in Annex A).
• Reporting: Test report must identify the sample, method (ISO 3961:2024), procedural deviations, results, date, and any unusual observations.

Applications

• Quality control and specification testing for edible oils, fats, biodiesel feedstocks, and oleochemical feed materials.
• Routine laboratory analysis for oilseed processors, refiners, food laboratories, research institutions, and regulatory agencies.
• Comparative assessments of unsaturation (degree of double bonds) for formulation, shelf-life estimation, and process control (hydrogenation, refining).

Practical notes & limitations

• Annex B’s calculated IV is influenced by impurities and thermal degradation products; calculated and volumetric IVs may diverge for cold‑pressed, crude/unrefined, or partially hydrogenated oils.
• Method not applicable to fish oils.
• Sampling and sample preparation reference ISO 5555 and ISO 661 respectively.

Related keywords: ISO 3961:2024, iodine value, IV determination, Wijs reagent, animal and vegetable fats and oils, fatty acid composition, volumetric titration, laboratory method.