Overview
EN ISO 23697-1:2025 addresses the determination of total bound nitrogen (ST-TNb) in water using the small-scale sealed tube method, specifically with the dimethylphenol colour reaction. Developed by CEN and identical to ISO 23697-1:2023, this European Standard provides a practical and reliable protocol for quantifying total nitrogen content in various water types, including groundwater, surface water, and wastewater. The method is applicable for nitrogen concentrations typically in the range of 0.5 mg/l to 220 mg/l, with adjustments possible depending on the tube system and sample composition.
The ability to accurately measure total bound nitrogen in water is essential for environmental management, as nitrogen pollutants from natural and human sources can adversely impact ecosystems via eutrophication and pose risks to public health.
Key Topics
-
Principle of Determination
The method is based on converting all forms of inorganic and organic nitrogen into nitrate through alkaline potassium persulfate oxidation, performed in a sealed tube under heating. The resulting nitrate reacts with 2,6-dimethylphenol in acidic conditions to form a coloured product, which is quantified using photometric or spectrophotometric analysis.
-
Sample Preparation and Measurement Range
- Suitable for a wide variety of waters, from clean groundwater to complex wastewaters.
- Measuring range depends on the sealed tube system; dilutions are recommended for samples with concentrations above the application range.
- Precision is highest near the middle of the application range.
-
Interferences and Quality Control
- Main interferences include certain metal ions, high chemical oxygen demand (COD), and chloride levels.
- Laboratories must check for interferences and validate results using standard reference materials and control samples as recommended in related ISO standards.
- Following equipment manufacturers' instructions is essential for correct results.
-
Practical Operation
- Multiple digestion temperatures (100 °C, 120 °C, or 170 °C) and digestion times can be applied, depending on the sealed tube system in use.
- Results are reported with appropriate uncertainty and significant digits following good laboratory practice.
Applications
This method is widely used in:
-
Water and Wastewater Treatment
Essential for performance monitoring, process control, and regulatory compliance in treatment facilities, given nitrogen's role in environmental eutrophication and water pollution.
-
Environmental Monitoring
Applied in routine monitoring of surface water bodies, helping authorities track and manage nutrient loads from agricultural run-off or urban discharge.
-
Industry and Quality Assurance
Useful for industries discharging water, such as food production or chemical manufacturing, to monitor effluents and ensure environmental standards are met.
-
Research and Method Validation
Provides a standardized approach for laboratories and research organizations to ensure comparability and reproducibility in nitrogen analysis.
Related Standards
For comprehensive water quality analysis and laboratory procedures, the following standards are relevant:
- ISO 11905-1: Water quality - Determination of nitrogen by oxidative digestion with peroxodisulfate.
- ISO 20236: Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb), and dissolved bound nitrogen (DNb).
- ISO 5667 Series: Guidance on water sampling techniques and sample handling (Parts 1, 3, and 10).
- ISO/IEC 17025: General requirements for the competence of testing and calibration laboratories.
- ISO 8466-1: Calibration and evaluation of analytical methods.
Practical Value
Implementing EN ISO 23697-1:2025 offers several practical benefits:
- Delivers reliable and consistent results for total bound nitrogen in a wide range of water matrices.
- Supports laboratories in meeting environmental compliance requirements.
- Enhances data comparability across monitoring programs in Europe and globally.
- Provides a procedural reference for accreditation under ISO/IEC 17025.
For laboratories, utilities, and regulators, this standard remains a critical tool for effective water quality management and environmental protection, leveraging the small-scale sealed tube method for accurate nitrogen monitoring.
