Overview
EN ISO 14891:2002 (ISO 14891 / IDF 185:2002) specifies a routine instrumental method for the determination of total nitrogen content in milk and milk products using combustion according to the Dumas principle. The procedure converts nitrogen compounds to molecular nitrogen by high‑temperature combustion (900 °C to 1 200 °C) in an oxygen atmosphere, removes interfering components, and quantifies nitrogen with a thermal conductivity detector. This standard is intended for routine laboratory analysis and national implementation across CEN members.
Key Topics and Requirements
- Principle: Combustion of a representative test portion in oxygen; conversion of nitrogen species to N2 and quantitative detection by thermal conductivity.
- Temperature range: Combustion tube operated at approximately 900 °C–1 200 °C (as specified).
- Gases: Use of high‑purity carrier gases such as carbon dioxide (CO2) or helium (He) and high‑purity oxygen (O2); specific purity grades are indicated for different sample nitrogen levels.
- Reagents and materials: Absorbents for sulfur compounds, copper oxide, platinum catalyst blends, silver wool, silica/quartz wool, copper or tungsten for reduction tubes, drying agents (e.g., phosphorus pentoxide or magnesium perchlorate), and support materials for combustion tube fill.
- Apparatus and calibration: Requirements for suitable Dumas apparatus design, calibration routines, oxygen‑demand control, detection/integration, and microprocessor‑based calculation of nitrogen content.
- Sampling and sample preparation: Guidance on representative sampling and preparation of liquid and solid milk product test portions for routine analysis.
- Quality and precision: Sections on calculation, expression of results, repeatability/reproducibility, interlaboratory testing, and reporting requirements.
- Informative annexes: Flowcharts and scheme examples for Dumas apparatus, calibration procedures, and a comparison with Kjeldahl results.
Applications and Users
EN ISO 14891:2002 is applicable where reliable routine measurement of nitrogen (and by extension protein estimation when using conversion factors) in dairy matrices is required. Typical users include:
- Dairy industry quality control laboratories
- Food testing and commercial analytical laboratories
- Regulatory and food safety authorities
- Research and development teams in dairy science
- Instrument manufacturers providing Dumas analyzers
This standard supports consistent, comparable results across laboratories and is useful when adopting an instrumental alternative to the Kjeldahl method for routine nitrogen determination.
Related Standards
- ISO 8968-1 / IDF 20-1 - Milk - Determination of nitrogen content - Part 1: Kjeldahl method (normative reference).
- EN ISO 14891 includes informative annex D comparing Dumas and Kjeldahl results for practical cross‑method evaluation.
Keywords: EN ISO 14891:2002, Dumas method, nitrogen determination, milk and milk products, combustion analysis, thermal conductivity detector, routine method, Kjeldahl comparison.
