Overview
ISO/TS 21231:2019 - Water quality - Characterization of analytical methods - Guidelines for the selection of a representative matrix provides guidance for laboratories to select or prepare representative matrices for the initial assessment of quantitative physico‑chemical water analysis methods. The technical specification helps determine method performance characteristics, including uncertainty, across typical water types such as waters intended for consumption, natural waters, waste waters, marine waters, and recreational waters. It also covers how to define scope, acceptable reference values, and reporting expectations.
Key topics and requirements
- Definition of representative matrix: A matrix is the set of sample constituents (excluding the analyte) that affect analytical behavior. The standard describes how to select matrices whose intrinsic characteristics match the samples a lab handles.
- Scope and assessment procedure: Laboratories must define the method scope (matrix types, analytes and concentration ranges) and decide whether to segment scope rather than validate a single overly broad method.
- Influence parameters: The document identifies parameters that can modify analytical results (common parameters include pH and other matrix properties such as salinity). For each analyte, performance must be assessed across relevant parameter ranges.
- Limits and verification: Definitions and requirements for limit of detection (LOD) and limit of quantification (LOQ) are included, with emphasis that LOD/LOQ shall be verified in the intended matrix.
- Available materials: Guidance on using real matrices (including reasonable dilution), artificial matrices, and analyte‑specific blank values. The specification offers selected recipes - e.g., four marine‑water and five waste‑water recipes - to support method characterization.
- Accepted reference values & reference materials: Describes acceptable ways to establish reference values (certified reference materials, inter‑laboratory consensus, reference methods, or target values).
- Documentation: Requirements for reporting characterization results and matrix descriptions (see Section 8).
Applications and users
ISO/TS 21231:2019 is intended for:
- Water quality laboratories conducting method validation, verification, or initial characterization
- Environmental monitoring and regulatory labs responsible for drinking water, wastewater, marine and recreational water analysis
- Method development teams and validation managers who must define method scope and uncertainty
- Accreditation bodies and auditors assessing laboratory competence and method applicability
Practical uses:
- Selecting representative matrices to determine method accuracy, precision and uncertainty
- Preparing artificial or diluted matrices to mimic field samples where CRMs are unavailable
- Verifying LOD/LOQ and identifying matrix interferences before routine deployment
Related standards
- ISO 5667-3 (Sampling - preservation and handling)
- ISO 6107 (Water quality - Vocabulary)
- ISO Guide 35 and ISO/TS 13530 referenced for reference material and certification concepts
Keywords: ISO/TS 21231:2019, water quality, representative matrix, analytical methods, method validation, uncertainty, LOD, LOQ, physico‑chemical analysis.
