Overview
ISO 7836:2024 - Natural rubber - Identification of phytosterols, including β-sitosterol specifies a laboratory method to detect the presence (presence/absence) of phytosterols, notably β‑sitosterol, in natural rubber in raw, vulcanised and latex forms. The standard uses acetone extraction followed by thin layer chromatography (TLC) with comparison to a β‑sitosterol standard. Results confirm whether natural rubber (which uniquely contains β‑sitosterol among cis‑1,4‑polyisoprene rubbers) is present.
Key topics and technical requirements
- Scope: Identification (qualitative) of phytosterols including β‑sitosterol in natural rubber (raw, vulcanised, latex).
- Extraction: Acetone extraction per procedure; 2–5 g sample; rotary evaporation (≤60 °C) and oven drying prior to re‑dissolution in acetone.
- TLC method:
- Silica gel plates activated (105 °C for 2 h or 80 °C overnight).
- Developing solvent: petroleum ether : diethyl ether (60:40 by volume).
- Spotting: 2–5 µl of sample and standard β‑sitosterol (>95 %).
- Spray reagent: cupric acetate + phosphoric acid solution; β‑sitosterol appears purple after spraying and drying.
- Identification: compare Rf of sample spot to standard; match within ±5 % confirms presence.
- Detection limit: minimum detection of natural rubber is approximately 3 %.
- Expression of results: reported as presence or absence of β‑sitosterol.
- Reporting requirements: include reference to ISO 7836:2024, sample identification, test result, detection limit, any deviations or unusual features, and test date.
Practical applications and users
- Quality control and raw‑material verification in the rubber industry - distinguishing natural rubber from synthetic cis‑1,4‑polyisoprene.
- Incoming goods inspection and supplier verification for tyre, automotive, pharmaceutical rubber goods and specialty elastomer manufacturers.
- Materials testing laboratories and forensic/materials analysts validating the botanical origin of rubber.
- Research and development groups performing composition analysis or product authentication.
Benefits:
- Simple, cost‑effective qualitative test using standard TLC equipment.
- Useful as a complementary method alongside polymer characterization techniques (e.g., FTIR, protein tests) to confirm natural rubber content.
Related standards
- ISO 124 - Latex, rubber - Determination of total solids content (referenced for latex sample prep).
- ISO 1407 - Rubber - Determination of solvent extract (referenced for extraction procedure).
Note: Users should follow normal laboratory safety practices. ISO provides the full procedural details and normative references in ISO 7836:2024.