Overview
ISO 9832:2002 specifies a laboratory method for determining residual technical hexane in animal and vegetable fats and oils. The standard uses a headspace gas‑chromatographic technique and is suitable for measuring hexane concentrations from 10 mg/kg to 1 500 mg/kg of fat or oil. The method is expressly not applicable to marine oils.
Key topics and technical requirements
- Principle: desorption of volatile hydrocarbons from a 5 g fat sample by heating at 80 °C in a closed vial, followed by analysis of the vial headspace by gas chromatography (GC) with a flame ionization detector (FID).
- Analytical range: 10–1 500 mg hexane per kg of fat/oil.
- Internal standard: n‑heptane is recommended (5 µL typical; 2 µL for very low levels). Cyclohexane may be used if compatible.
- Calibration: use calibration fat (freshly refined, deodorized) spiked with technical hexane (or n‑hexane). Typical calibration produces a mean calibration factor F ≈ 0.45 for n‑heptane (≈0.57 for cyclohexane).
- Sample size & handling: weigh 5 g test portion into 20 mL septum vials; add internal standard; equilibrate in a thermostatted bath at 80 °C for 60 min.
- Headspace sampling: withdraw 1 000 µL of headspace gas with a warmed (≈60 °C) gas‑tight syringe and inject immediately into the GC.
- GC system: either a packed column (2–4 m, coated with 10% squalane or similar) or a capillary column (~30 m, methylpolysiloxane). Injector and detector temperatures 100 °C, oven 50 °C; use a 1/100 split for capillary columns.
- Precision & validation: interlaboratory precision data and repeatability/reproducibility limits are provided in informative Annex A; collaborative tests (FOSFA-organized) inform expected performance. Referenced sampling/preparation standards include ISO 661 (sample preparation) and ISO 5555 (sampling recommendation).
Applications and users
ISO 9832 is intended for:
- Quality control laboratories in edible oil refining and processing (vegetable and animal fats).
- Food safety and regulatory agencies monitoring solvent residues.
- Contract testing laboratories performing compliance testing for residual hydrocarbon solvents.
- Industry trade associations and auditors validating solvent removal after extraction processes (e.g., hexane-extracted oils).
Practical benefits include standardized, comparable results for residual hexane, supporting product safety declarations, regulatory compliance, and process optimization.
Related standards
- ISO 661:1989 - Preparation of test sample (normative reference in ISO 9832)
- ISO 5555 - Recommended sampling methods (referred to for sampling)
- ISO 5725 - Precision of measurement methods (used for interlaboratory analysis)
Keywords: ISO 9832, residual hexane, technical hexane, headspace GC, fats and oils testing, GC‑FID, solvent residues, edible oil quality.
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