Overview
ISO 6866:1985 specifies a laboratory method for the determination of free and total gossypol in cottonseed, cottonseed meals and cakes used as animal feeding stuffs. The procedure uses solvent extraction in the presence of 3-aminopropane-1-ol (amino‑propanol), conversion of gossypol to a gossypol‑dianiline derivative using aniline, and measurement of absorbance at the wavelength of maximum absorbance (between 435 and 445 nm) by spectrophotometry.
The method provides routine analytical parameters useful for feed safety, quality control and regulatory compliance where gossypol concentrations are of concern.
Key Topics
- Scope: Applicable to cottonseed, cottonseed meals and cakes; also suitable for compound feeds containing these materials.
- Extraction solvents:
- Free gossypol: mixture of 2‑propanol and hexane (60:40 v/v) in presence of amino‑propanol
- Total gossypol: dimethylformamide (DMF)
- Derivatization: Conversion to gossypol‑dianiline by reaction with aniline to develop a measurable chromophore.
- Measurement: Spectrophotometric absorbance read at 435–445 nm using 10 mm cuvettes.
- Limits of detection: Free gossypol ~ 20 mg/kg; total gossypol ~ 50 mg/kg.
- Apparatus: standard laboratory glassware, agitator/shaker, water bath for heating, spectrometer and cuvettes.
- Sample mass guidance: For free gossypol in seeds/meals/tourteaux, sample mass should not exceed 1 g (compound feeds up to 5 g). For total gossypol, sample mass typically 0.5–5 g.
- Performance: Repeatability criteria are specified (e.g., differences between duplicate determinations not exceeding 15% for concentrations <500 mg/kg and 10% for >750 mg/kg).
Applications
- Feed safety and quality control: Routine monitoring of cottonseed products and derived feeds to manage gossypol toxicity risk in livestock.
- Laboratory testing: Standardized method for accredited testing laboratories and contract testing services.
- Regulatory compliance: Supports conformance with limits or advisory thresholds where gossypol monitoring is required.
Practical advantages include established solvent systems, a clear derivatization and absorbance measurement step, and defined detection and repeatability parameters that support reproducible results across laboratories.
Related Standards
- ISO 6497 - Animal feeding stuffs - Sampling (referred to for sample collection)
- ISO 6498 - Animal feeding stuffs - Preparation of test samples (sample preparation guidance)
For implementation, laboratories should follow ISO 6866:1985 alongside ISO 6497 and ISO 6498 to ensure representative sampling and correct sample preparation prior to chemical analysis. Ensure all reagents and equipment meet analytical quality specifications and observe reagent stability notes provided in the standard.