ISO 5983-2:2009

Overview

ISO 5983-2:2009 - "Animal feeding stuffs - Determination of nitrogen content and calculation of crude protein content - Part 2: Block digestion and steam distillation method" - specifies a semi‑micro, rapid routine Kjeldahl method for measuring Kjeldahl nitrogen in animal feeding stuffs, pet foods and their raw materials. The method uses block digestion, a copper catalyst, and steam distillation into boric acid, with subsequent titration to determine ammonia and calculate crude protein by the conventional conversion factor 6.25.

Key scope limits:

• Applicable to samples with > 0.5% mass fraction Kjeldahl nitrogen.
• Does not measure oxidized nitrogen forms or heterocyclic nitrogen compounds.
• Does not distinguish protein nitrogen from non‑protein nitrogen.

Key topics and technical requirements

• Principle: Conversion of organic nitrogen to ammonium sulfate by concentrated sulfuric acid and potassium sulfate (to raise boiling point), catalysed by copper; alkali liberation of NH3; steam distillation into boric acid; titration (colorimetric or potentiometric).
• Reagents: concentrated H2SO4 (≥98%), Kjeldahl catalyst tablets (K2SO4 + CuSO4·5H2O), H2O2, NaOH (~40%), boric acid trapping solution, HCl standard titrant (e.g., 0.1000 mol·L−1).
• Apparatus: digestion block (maintained ≈420 °C), steam distillation unit (manual, semi‑automatic or automatic), burette/automatic titrator with pH electrode, analytical balance (0.1 mg readability).
• Sample sizes: guidance provided (≈1.0 g for 3–30% protein; ≈0.5 g for 30–80%; ≈0.3 g for >80%; do not exceed 1.2 g).
• Quality control: reagent blanks, recovery/standard materials (acetanilide, tryptophan, ammonium sulfate), precision data (repeatability/reproducibility) and proficiency testing results are included.
• Safety: warns about hazardous reagents and operations (appropriate lab safety needed).

Applications

• Routine quality control and compositional analysis of animal feed, pet food and raw feed ingredients.
• Regulatory compliance testing where crude protein declarations are required.
• Research and product formulation to monitor protein levels and batch consistency.
• Feed mill and laboratory workflows that require a rapid, semi‑micro Kjeldahl routine method.

Who should use this standard

• Feed testing laboratories and contract analytical labs
• Feed manufacturers and QA/QC teams
• Regulatory bodies and inspection labs
• Academic and applied researchers in animal nutrition

Related standards

• ISO 5983-1 (Kjeldahl method, other variants)
• ISO 1871 (general Kjeldahl guidelines)
• ISO 6498 / ISO 6497 (sampling and sample preparation guidance for animal feeding stuffs)

Keywords: ISO 5983-2:2009, Kjeldahl method, block digestion, steam distillation, crude protein, animal feeding stuffs, pet food testing, boric acid titration, copper catalyst.