Overview
SIST EN ISO 23697-2:2026 specifies the method for determining total bound nitrogen (ST-TNb) in water using small-scale sealed tubes and the chromotropic acid colour reaction. This international standard applies to a wide range of water types, including groundwater, surface water, and wastewater, and is designed for concentrations generally between 0.5 mg/l and 150 mg/l. The procedure utilizes heated alkaline potassium persulfate oxidation and subsequent chromotropic acid colorimetry, offering a practical, reliable, and standardized approach for nitrogen analysis in water samples.
Key benefits:
- Ensures precise and comparable nitrogen measurements
- Supports compliance with water quality regulations
- Facilitates environmental monitoring and pollution control
Key Topics
- Total Bound Nitrogen (ST-TNb): Sum of all inorganic and organic nitrogen forms in water, including nitrate, nitrite, ammonia, and organic nitrogen.
- Small-Scale Sealed Tube Method: Utilizes commercially available prefilled glass tubes for simplified sample handling and consistent reagent dosing.
- Chromotropic Acid Colour Reaction: After oxidation to nitrate, a colorimetric reaction with chromotropic acid enables quantification using a photometer or spectrophotometer.
- Oxidation Process: Heated alkaline potassium persulfate ensures conversion of all nitrogen species to nitrate for accurate measurement.
- Measuring Range and Adaptability: Tube selections and sample dilutions accommodate a concentration range from 0.5 mg/l to 150 mg/l, covering most environmental and wastewater monitoring needs.
- Quality Control: Emphasizes calibration with reference materials, system checks for interferences, and adherence to ISO/IEC 17025 laboratory competence requirements.
- Interference Management: Addresses potential interferences from metal ions, organic loads, and chloride, with recommendations for dilution or spiking tests.
Applications
- Environmental Monitoring: Widely used in the routine analysis of groundwater, surface water, and effluents to track nitrogen pollution and support water protection strategies.
- Regulatory Compliance: Assists laboratories, water utilities, and industries in meeting local, national, and international water quality standards and permits.
- Wastewater Treatment: Important for optimizing nitrogen removal processes and verifying the effectiveness of denitrification systems in wastewater treatment plants.
- Agricultural Impact Assessment: Enables evaluation of fertilizer runoff and its contribution to nitrogen levels in water bodies, aiding in the management of eutrophication risks.
- Public Health Protection: Provides reliable data to assess potential health risks associated with elevated nitrogen concentrations in drinking water sources.
Related Standards
- ISO 23697-1: Water quality – Determination of total bound nitrogen (ST-TNb) in water using small-scale sealed tubes – Part 1: Standard method.
- ISO 11905-1: Water quality – Determination of nitrogen – Part 1: Method using oxidative digestion with peroxodisulfate, a reference for oxidation principles.
- ISO 20236: Water quality – Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb), and dissolved bound nitrogen (DNb) after high temperature catalytic oxidative combustion.
- ISO 5667-1, ISO 5667-3, ISO 5667-10: Guidance on water sample collection, preservation, and sampling of wastewater.
- ISO/IEC 17025: General requirements for the competence of testing and calibration laboratories, relevant for quality control.
Practical Value
Adopting SIST EN ISO 23697-2:2026 ensures water analysis laboratories perform consistent, accurate, and internationally comparable measurements of total bound nitrogen. Its user-friendly small-scale sealed tube approach minimizes errors, increases throughput, and simplifies complex chemical reactions using safe, pre-dosed solutions. The method is highly valued where reliable data is required for environmental management, compliance verification, and safeguarding public health against nitrogen-related pollution and eutrophication.
Keywords: water quality, total bound nitrogen, ST-TNb, chromotropic acid, small-scale sealed tubes, nitrogen in water, environmental monitoring, wastewater analysis, ISO 23697-2, water analysis standard
