Overview
ISO 21033:2016 specifies an inductively coupled plasma optical emission spectroscopy (ICP-OES) method for the determination of trace elements in animal and vegetable fats and oils. The method covers most vegetable oils (crude, degummed, refined, bleached, deodorized, hardened), lecithins and phosphatides, provided the elements are in a solubilized form. Milk and milk-derived fats are excluded. The standard emphasizes proper sample dilution and instrumental standardization to achieve accurate trace-element quantification.
Key topics and technical requirements
- Analytical principle: Direct aspiration of solvent-diluted oil into an ICP-OES; element quantification by characteristic emission lines.
- Sample preparation: Follow ISO 661 for test-sample preparation (do not clarify). Melt and homogenize solids, keep diluted samples warm (max 60 °C for hardened fats).
- Dilution solvents: 1‑butanol (preferred), kerosene or xylene - samples, blanks and standards must use the same solvent. Typical dilution is 1:1 (sample:solvent) or specified multi-step dilutions for lecithins.
- Standards and blanks: Use organics-compatible multi-element standards; blank oil (refined/bleached) and Base oils (Base 20/75) to verify blank purity. Multi-level calibration (e.g., 2.5, 5, 10 mg/kg) recommended.
- Internal standard: Optional yttrium or scandium (typical 10 mg/kg in final dilution; add 20 mg/kg to diluent).
- Instrument setup and QC: Warm instrument, profile per manufacturer, scan triplicates, restandardize every ≤10 samples. Watch for calibration drift (carbon build-up).
- Limitations: Not suitable for samples containing fine particles (bleaching earth, metal particles, rust) - these cause poor recovery due to nebulization/atomization problems. For particulate samples, graphite furnace atomic absorption spectrometry (GFAAS) is the only suitable non-ashing direct alternative.
- Selected detection limits (examples from the standard): Ca, Cu, Fe, Mg, Ni, P ~0.05 mg/kg; Si, Na ~0.1 mg/kg; S ~1 mg/kg.
Applications and users
- Who uses it: analytical laboratories, food and edible‑oil producers, quality control teams, regulatory agencies, and instrument manufacturers validating ICP-OES methods for oils.
- Practical uses: routine quality control of trace metals in edible oils and lecithins, contamination investigations, supplier testing, and regulatory compliance where trace element profiles are required.
Related standards
- ISO 661 (sample preparation)
- ISO 5555 (sampling guidance)
- EN 14538:2006 and ISO 10540-3:2012 (emission lines and instrument setup)
- ISO 6353 series (reagent grades)
- Reference alternative: graphite furnace AAS for particulate-bearing samples
ISO 21033:2016 is essential for reliable ICP-OES trace-element analysis of oils - ensuring consistent sample dilution, solvent choice, calibration practice and awareness of particulate limitations.