Overview
EN ISO 5983-1:2005 - "Animal feeding stuffs - Determination of nitrogen content and calculation of crude protein content - Part 1: Kjeldahl method" (CEN adoption of ISO 5983-1:2005) specifies the internationally accepted Kjeldahl procedure for measuring nitrogen content in animal feeds and calculating crude protein. The method covers digestion, distillation and titration steps, required reagents and apparatus, sample preparation and quality checks. It is widely referenced for regulatory, quality-control and laboratory testing of animal feeding stuffs.
Key topics and technical requirements
- Scope & limitations
- Determines total Kjeldahl nitrogen (TKN); does not measure oxidized nitrogen forms or heterocyclic nitrogen compounds.
- Does not distinguish protein vs non-protein nitrogen; use alternative methods if non-protein nitrogen must be quantified.
- Principle
- Organic material is digested with sulfuric acid and a catalyst to convert nitrogen to ammonium sulfate; alkalisation liberates ammonia which is distilled and quantified by titration. Crude protein is calculated by multiplying nitrogen by a conventional factor.
- Reagents & materials
- Potassium sulfate, copper catalyst (CuO or CuSO4·5H2O), concentrated sulfuric acid, NaOH solution, collecting liquids (dilute sulfuric acid or boric acid), titrants, mixed indicator; standard check materials include acetanilide and tryptophan.
- Apparatus
- Kjeldahl digestion flasks, heating/digestion equipment, distillation unit, titration setup or pH meter for endpoint detection, analytical balance.
- Procedure essentials
- Representative sample preparation per ISO 6498; weigh appropriate test portion to contain specified nitrogen mass; digest (heat + catalyst + K2SO4), cool, dissolve sulfates, add NaOH, distil ammonia into collecting solution, titrate (or perform simultaneous titration).
- Quality control
- Blank tests (sucrose), check tests with certified standards, precision data and reporting requirements included.
Applications
- Routine laboratory analysis of animal feed ingredients and finished feeds for:
- Nutritional labelling and formulation (crude protein determination)
- Quality control in feed production
- Regulatory compliance and batch release testing
- Research on feed composition and digestibility
Who uses this standard
- Feed-testing laboratories, quality assurance teams at feed mills, regulatory bodies, research institutions, and certification/inspection organizations requiring standardized, traceable nitrogen/crude protein measurement.
Related standards
- ISO 5983-2:2005 - Block digestion/steam distillation method (complementary technique)
- ISO 6498 - Preparation of test samples (sample prep guidance referenced)
- ISO 6497 - Recommended sampling methods for animal feeding stuffs
- ISO 1871 - General directions for the Kjeldahl method
Keywords: EN ISO 5983-1:2005, Kjeldahl method, animal feeding stuffs, nitrogen determination, crude protein, feed analysis, CEN standard.