Overview
ISO 16634-1:2008 specifies a standardized laboratory method for determining total nitrogen by combustion (the Dumas principle) and calculating crude protein in oilseeds and animal feeding stuffs. The standard defines scope, principle, required reagents and apparatus, sample preparation, test procedure, calculation of results and precision requirements. Like the Kjeldahl method, ISO 16634-1:2008 does not distinguish protein nitrogen from non‑protein nitrogen and uses conversion factors (usually 6.25) to express nitrogen as crude protein.
Keywords: ISO 16634-1:2008, Dumas method, total nitrogen, crude protein, oilseeds, animal feeding stuffs, combustion analysis
Key topics and technical requirements
- Principle: Combustion of a homogenized test sample, removal of interfering gases, conversion of nitrogen compounds to N2, and quantitative measurement by a thermal conductivity detector (TCD).
- Apparatus: A Dumas analyser with furnace (≥ 850 °C), TCD, oxygen and carrier gases (He or CO2), post‑combustion catalysts (CuO, Pt on Al2O3), reduction materials (copper), and drying/absorbent traps.
- Reagents & gases: High‑purity oxygen and carrier gas; drying agents (P2O5 or Mg(ClO4)2); nitrogen‑free reagents; certified reference materials (e.g., amino‑acid standards) for calibration.
- Sample prep: Grinding to specified particle sizes and sieving (typical cutoffs 800 µm or 1 mm), control of moisture (ISO 665/ISO 6496), and representative laboratory sampling according to referenced ISO methods.
- Procedure controls: Instrument calibration, control of oxygen demand, test portion sizing, detection/integration settings, and calculation of nitrogen mass fraction and conversion to crude protein.
- Performance: Precision, repeatability and reproducibility are addressed; informative annexes provide calibration guidance, conversion factor examples, and interlaboratory study results.
Applications and users
ISO 16634-1:2008 is used by:
- Commercial and regulatory food and feed testing laboratories measuring protein in seeds, meals and animal feeds.
- Feed manufacturers and quality control teams for ingredient specification and formulation.
- Agricultural and commodity traders verifying protein content in oilseeds (soybean, canola, sunflower).
- Instrument manufacturers and method developers validating Dumas analysers.
Advantages include faster throughput and elimination of hazardous chemicals compared with Kjeldahl testing.
Related standards
This standard is essential when accurate, reproducible combustion‑based determination of total nitrogen and crude protein in oilseeds and animal feeds is required.