Overview
ISO/TS 5667-25:2022 - Water quality - Sampling - Part 25 - provides a practical guideline for the validation of the storage time of water samples. It describes test plans and operating methodologies to determine the maximum acceptable delay before analysis (MaxADs) for chemical and physico-chemical analytes in aqueous matrices. The document covers how to verify sample stability under specified preservation conditions (temperature, light, matrix, container, addition of stabilizer, etc.). Biological and microbiological methods are explicitly excluded.
Keywords: ISO/TS 5667-25:2022, water quality sampling, storage time validation, sample stability, MaxADs.
Key Topics
- Scope and principles: Framework for planning stability studies and defining acceptance criteria (MADs - maximum acceptable deviation).
- Analytical method prerequisites: Requirement for an analytical method with characterized performance (repeatability, intermediate precision, trueness, accuracy and uncertainty) before conducting stability studies.
- Study design and matrices: Guidance on selecting representative water matrices (surface water, groundwater, drinking water, industrial/residual waters) and concentration levels.
- Test plans and experimental design:
- Chronological stability studies
- Isochronous stability studies
- Type 1 and Type 2 pseudo-isochronous studies
- Randomization and batch preparation
- Influence parameters of preservation: Temperature, light exposure, container material, chemical stabilizers and other storage conditions.
- Data handling and validation: Graphic representation, initial validation at time T, validation at subsequent times, determination of MaxADs and reporting of stability.
- Annexes and examples: Measurement process, fundamental concepts, influence-parameter studies and worked example (e.g., atrazine stability).
Applications
ISO/TS 5667-25:2022 is designed for organizations that need to ensure reliable chemical and physico-chemical water data by validating how long samples remain stable under defined storage/preservation conditions. Typical users include:
- Environmental and drinking-water testing laboratories
- Regulatory agencies and conformity assessment bodies
- Water resource managers and utilities
- Environmental consultancies and monitoring programmes
- Method developers and accreditation assessors
Practical uses:
- Establishing laboratory-specific holding times (MaxADs) for routine analyses
- Designing stability studies to support method validation or regulatory submissions
- Choosing preservation methods (temperature, container, stabilizers) to maintain sample integrity
- Improving data comparability and reducing measurement uncertainty in monitoring programs
Related Standards
- ISO/TS 21231 - Characterization of analytical methods; selection of representative matrix
- ISO 5667 series - General water sampling guidance (e.g., ISO 5667-3:2018 on sample integrity)
- ISO Guide 35 - Reference material stability and homogeneity guidance
Using ISO/TS 5667-25:2022 helps laboratories produce robust, harmonized stability data that support reliable water-quality measurement and regulatory compliance.
