Overview
ISO 10539:2002 specifies a standardized laboratory method for the determination of alkalinity in animal and vegetable fats and oils. The method measures the proportion of alkali (reported as milligrams of oleate per kilogram or as a mass fraction of sodium hydroxide) by titration after dissolving the sample in a heated acetone/water mixture. The standard excludes fats with acidity greater than 60% (by ISO 660) and does not detect whether solid fats have been caustically treated.
Key topics and requirements
- Principle: dissolve the test portion in an acetone/water solution (with bromophenol blue indicator), heat, allow phase separation and titrate the acetone layer with standardized HCl.
- Reagents:
- Laboratory-grade water (ISO 3696, grade 3)
- Acetone/water indicator solution (acetone, water, bromophenol blue; alkalized with NaOH 0.1 mol·L–1 then back-titrated with HCl 0.1 mol·L–1)
- Titrant: HCl standardized to c = 0.01 mol·L–1 (fresh within 7 days)
- Apparatus: borosilicate glassware for acetone solution, 400–500 mL wide-neck conical flasks, magnetic stirrer and heated plate recommended, burette for titration.
- Sample mass: sample sizes vary by expected alkalinity and sample colour (typically 1 g to 40 g; larger masses for low expected alkalinity or light-coloured fats).
- Result expression: alkalinity may be calculated as:
- Mass fraction of NaOH (A): A = (4 · V · c) / m
- Oleate content (S, mg/kg): S = (V · c · 304 000) / m
where V = volume of HCl (mL), c = molarity of HCl (mol·L–1), m = sample mass (g).
- Repeatability and reproducibility: Annex A reports interlaboratory trial data and provides r/R values and statistical guidance per ISO 5725.
Applications and users
ISO 10539:2002 is used by:
- Food and edible oil testing laboratories for quality control and specification compliance
- Oilseed processors, refiners and manufacturers of animal/vegetable fats
- Regulatory and conformity assessment bodies verifying product purity
- Analytical chemists developing or validating methods involving alkali residues
Practical uses include detecting residual soaps or basic contaminants in fats and oils, supporting refining process control and product release decisions.
Related standards
- ISO 660 - Determination of acid value and acidity
- ISO 661 - Sample preparation for analysis of fats and oils
- ISO 5555 - Sampling of fats and oils
- ISO 3696 - Water for laboratory use
- ISO 5725 - Method accuracy (repeatability and reproducibility)
Keywords: ISO 10539:2002, alkalinity determination, animal and vegetable fats and oils, titration, acetone/water, HCl titration, oleate mg/kg, laboratory method.