Overview
ISO 24698-1:2018 specifies a standardized laboratory method for determining the bound acrylonitrile content in acrylonitrile‑butadiene rubber (NBR) using an automatic analyser based on the Dumas combustion (combustion) method. The method is also applicable to XNBR (carboxylic NBR), NBIR (acrylonitrile‑butadiene‑isoprene rubber) and NBR latex. Note: ISO 24698‑1 and ISO 24698‑2 can produce different results on the same sample because they use different analytical principles.
Key topics and technical requirements
- Principle: Sample nitrogen is converted to oxides of nitrogen during high‑purity oxygen combustion, reduced to elemental nitrogen, separated from CO2 and H2O, then measured by a thermal conductivity detector (TCD). The measured nitrogen content is converted to bound acrylonitrile content by a factor (ISO provides the conversion formula: bound acrylonitrile = 37.9 × nitrogen mass %).
- Apparatus components:
- Combustion unit and high‑purity oxygen feeder
- Reduction unit and absorber/separator for CO2/H2O
- Carrier gas feed and TCD
- Microprocessor for calibration and result calculation
- Performance checks: Calibration and accuracy demonstrated using reference materials (e.g., L‑aspartic acid, L‑glutamic acid, EDTA). Ten successive determinations should have a mean within ±0.2 percentage points of the theoretical value and a relative standard deviation ≤ 0.5 % (by mass % nitrogen).
- Reagents & gases: Oxygen (≥99.99 %), carrier gases such as helium, carbon dioxide or argon (≥99.995 %), ethanol, methanol.
- Sampling & preparation:
- Raw rubber: milling (nip ~0.2 mm, roll surface ~100 °C), solvent extraction with ethanol per ISO 1407 (method C), drying until mass change ≤ 2.0 mg over 10 min.
- Latex: coagulation in ethanol/methanol, washing, milling and drying as above.
- Procedure: Weigh test portion (50–500 mg) targeting 5–15 mg total nitrogen per test, combust, reduce and detect nitrogen, then calculate bound acrylonitrile.
- Precision: Interlaboratory test programme (2006) assessed method precision (see Annex B).
Applications and who uses it
- Quality control labs in rubber manufacturing to verify monomer incorporation in NBR grades.
- Raw material suppliers and incoming‑goods inspection to confirm acrylonitrile content.
- R&D and formulation teams assessing batch‑to‑batch consistency or new polymer grades (NBR, XNBR, NBIR, NBR latex).
- Independent testing laboratories and certification bodies performing standardized compositional analysis.
- Useful for product specifications, supplier audits and material traceability.
Related standards
- ISO 24698‑2 (alternative method - may yield different results)
- ISO 1795 (sampling and preparative procedures for raw rubber)
- ISO 1407 (solvent extract determination; Method C referenced for extraction)
- ISO 123 (rubber latex sampling)
This ISO 24698‑1:2018 guidance ensures reproducible determination of bound acrylonitrile content using the Dumas combustion technique and supports consistent quality control and material specification across the rubber industry.
Open preview (PDF)Rubber, raw — Determination of bound acrylonitrile content in acrylonitrile-butadiene rubber (NBR) — Part 1: Combustion (Dumas) method