Overview
EN ISO 6320:2017 (ISO 6320:2017) specifies a standardized method for the determination of refractive index of animal and vegetable fats and oils. The procedure covers sample preparation, instrument calibration, measurement temperatures and calculation rules for reporting refractive index values. Milk and milk‑derived fats are excluded from the scope.
Key topics and technical requirements
- Scope: Measurement of refractive index for animal and vegetable fats and oils (excludes milk fats).
- Instruments: Abbé‑type refractometers or modern digital refractometers; instrument accuracy to ±0.0001 over n = 1.300–1.700.
- Light source: Sodium vapour lamp (or white light with achromatic compensation).
- Temperature control: Prism temperature must be maintained and monitored; water baths with thermostatic control (±0.1 °C) are used for temperature stability.
- Calibration: Verify calibration using a glass plate of known refractive index or ethyl laurate of known refractive index.
- Sample prep: Follow ISO 661 for preparation; determine refractive index on dried and filtered fats and oils. Solid samples must be fully melted and temperature‑stabilized before measurement.
- Measurement temperatures: Typical reference temperatures are 20 °C, 40 °C, 50 °C, 60 °C, 80 °C or higher, chosen depending on melting behavior of the sample.
- Cleaning reagents: Solvents such as hexane, light petroleum, acetone or toluene are recommended for prism cleaning.
- Procedure & calculation:
- Take three independent readings and report the arithmetic mean to four decimal places.
- If measurement temperature differs from the reference by
