Overview
ISO 9297:1989 is an international standard published by the International Organization for Standardization (ISO) that specifies a method for the determination of dissolved chloride in water. This method, commonly known as Mohr’s method, uses silver nitrate titration with a chromate indicator to quantify chloride concentrations. It addresses the need for accurate water quality analysis, essential for environmental monitoring, industrial processes, and public health protection.
The standard is applicable for chloride concentrations between 5 mg/l and 150 mg/l. Through sample dilution or the use of larger burettes, the range may be extended up to 400 mg/l. However, it is not suitable for heavily polluted waters with low chloride content due to potential interferences.
Key Topics
- Scope of Application
- Suitable for natural waters, rainwater, potable water, and some wastewaters.
- Designed for direct determination of dissolved chloride.
- Analytical Principle
- Chloride ions react with silver ions, forming insoluble silver chloride.
- The endpoint is detected using chromate ions as an indicator, which form a red-brown silver chromate once all chloride has been precipitated.
- Interferences and Limitations
- Substances such as bromides, iodides, sulfides, cyanides, ammonium, thiosulfate, and certain iron and sulfite ions can interfere with accurate results.
- Heavily polluted or highly colored and turbid water may affect endpoint detection or cause overestimation.
- Required Equipment and Reagents
- Laboratory burette (typically 25 ml or higher).
- Standard solutions and reagents as specified, such as silver nitrate, potassium chromate, and sodium chloride.
- Procedural Considerations
- Maintain sample pH between 5 and 9.5.
- Perform blank tests and apply corrections as necessary.
- Document all sample adjustments and deviations from the standard procedure.
Applications
Implementing ISO 9297:1989 delivers consistent, repeatable results for analyzing chloride levels in various water types. Key applications include:
- Environmental Monitoring
- Assessing water bodies for pollution or natural chloride variation.
- Ensuring compliance with environmental regulations regarding water quality.
- Drinking Water Testing
- Confirming water safety for public consumption by detecting excessive chloride.
- Industrial Use
- Monitoring process water quality in manufacturing and energy production.
- Quality assurance for food and beverage processing where water purity is critical.
- Wastewater Management
- Evaluating the effectiveness of treatment processes.
- Supporting discharge compliance and water reuse planning.
Related Standards
Professionals using ISO 9297:1989 may also benefit from related ISO standards to ensure comprehensive water sampling, analysis, and reporting:
- ISO 385-1:1984 – Laboratory glassware – Burettes – General requirements
- ISO 5667-1:1980 – Water quality – Sampling – Design of sampling programmes
- ISO 5667-2:1982 – Water quality – Guidance on sampling techniques
- ISO 5667-3:1985 – Water quality – Preservation and handling of samples
- ISO 5725:1986 – Precision of test methods – Determination of repeatability and reproducibility
These related guidelines support proper sampling, equipment selection, and statistical evaluation of water quality data, contributing to robust water analysis programs.
Keywords: ISO 9297:1989, water quality, chloride determination, Mohr’s method, silver nitrate titration, chromate indicator, water analysis standard, dissolved chloride, environmental monitoring, laboratory water testing, volumetric analysis.