Overview
EN ISO 3656:2011/A1:2017 is Amendment 1 to ISO 3656:2011 adopted by CEN (published May 2017). The document updates the international method for determining ultraviolet (UV) absorbance expressed as specific UV extinction of animal and vegetable fats and oils. The amendment clarifies scope (excluding milk and milk‑derived fats), refines instrument verification procedures, and adds procedural and bibliographic references to improve photometric accuracy and linearity checks.
Key topics and technical requirements
- Scope: Method for measuring UV absorbance of animal and vegetable fats and oils. Milk and milk products (and fats obtained from them) are excluded.
- Instrument verification (Absorbance scale):
- Recommends checking linearity and photometric accuracy using potassium dichromate in perchloric acid sealed in far‑UV quartz cells (40, 60, 80, 100 mg/l) measured against a perchloric acid blank.
- Provides an alternative preparation in 0.01 N sulfuric acid (detailed dilution steps) to produce four solutions for linearity checks; acceptable linearity R > 0.99.
- Example specific extinction limits for a 60 mg/l potassium dichromate solution measured in a 1 cm cuvette:
- 235 nm: 124.5 (122.9–126.2)
- 257 nm: 144.0 (142.4–145.7)
- 313 nm: 48.6 (47.0–50.3)
- 350 nm: 106.6 (104.9–108.2)
- Alternate check with potassium chromate in KOH at 275 nm (extinction ~0.200 ± 0.005 in 1 cm cuvette).
- Safety warning: Potassium dichromate/chromate are classified as CMR (carcinogenic, mutagenic, reprotoxic). Procedures must avoid skin contact and inhalation.
- Annex A: Examples/tests performed on representative oil samples (extra virgin olive oil, refined olive‑pomace oil, blends with rapeseed/soybean/high‑oleic sunflower oils).
- Bibliography: Adds reference to European Pharmacopoeia 2.2.25 (UV/visible absorption spectrophotometry).
Applications and users
This amendment supports reliable UV spectrophotometric testing used in:
- Quality control laboratories in edible oil production and refining
- Olive oil grading and authenticity testing (e.g., extra virgin classification)
- Food testing laboratories, regulators and standards bodies
- Manufacturers of analytical equipment and reference materials
Users rely on these verification steps to ensure photometric accuracy, linearity and traceability of UV extinction results for compliance, quality assurance and comparative testing.
Related standards and references
- ISO 3656:2011 (base method) - now amended by A1:2017
- EN ISO 3656:2011/A1:2017 (CEN adoption)
- European Pharmacopoeia - 2.2.25 Absorption spectrophotometry, ultraviolet and visible
Keywords: UV absorbance, specific UV extinction, animal and vegetable fats and oils, EN ISO 3656:2011/A1:2017, spectrophotometry, potassium dichromate, photometric accuracy, oil quality control.
