SIST EN 25663:1996

Overview

EN 25663:1993 (equivalent to ISO 5663:1984) specifies a laboratory procedure for the determination of Kjeldahl nitrogen after mineralization with selenium. The method is designed to quantify trivalent (Kjeldahl) nitrogen in a variety of water matrices, including raw, potable and waste waters. It is a standardized approach published by CEN to support consistent water quality assessment and laboratory analysis.

This standard clarifies the scope and limitations of the selenium-mineralization Kjeldahl technique. Notably, certain organic nitrogen forms - such as azide, azine, azo, hydrazone, nitrite, nitro, nitroso, oxime and semicarbazone - are not determined quantitatively by this procedure.

Key Topics

• Scope and applicability: Procedure applicable to raw, drinking (potable) and wastewater samples for the determination of trivalent nitrogen.
• Mineralization approach: Uses selenium-assisted mineralization prior to Kjeldahl nitrogen determination (as per ISO 5663:1984 equivalence).
• Limitations: Explicitly excludes quantitative determination of specific organic nitrogen derivatives (listed in the standard).
• Standardization and provenance: Adopted by CEN and aligned with ISO 5663:1984; intended for routine analytical use in accredited laboratories.

Applications

The EN 25663:1993 method provides practical value across laboratory and environmental monitoring contexts:

• Routine water quality monitoring: Suitable for municipal and industrial laboratories assessing nitrogen load in influent and effluent streams.
• Potable water analysis: Supports evaluation of nitrogen species that affect drinking water treatment and compliance checks.
• Wastewater treatment control: Helps monitor organic and ammoniacal nitrogen transformations where Kjeldahl nitrogen is a relevant parameter.
• Regulatory and reporting: Provides a standardized basis for reporting trivalent nitrogen results in conformity with regional or national requirements.

Benefits include repeatability when performed under controlled laboratory conditions, alignment with international practice (ISO), and clear scope statements that guide interpretation of results.

Related Standards

• ISO 5663:1984 - Original international method for Kjeldahl nitrogen determination after selenium mineralization (EN 25663:1993 is equivalent).
• Other related water-quality and nitrogen-analysis standards address alternative digestion reagents, total nitrogen methods, or methods for specific nitrogen species (consult local regulatory frameworks for applicable complementary standards).

For laboratories implementing EN 25663:1993, ensure personnel are trained in Kjeldahl procedures and that method limitations (excluded organic nitrogen forms) are considered when interpreting results for regulatory or research purposes.