ISO 33403:2024

Overview

ISO 33403:2024 - Reference materials - Requirements and recommendations for use - provides practical guidance on the correct use of reference materials (RMs) and certified reference materials (CRMs) in measurement processes. It explains how RMs and CRMs support measurement traceability, calibration, quality control, assignment of values, and the establishment of conventional scales. This first edition replaces ISO Guide 33:2015 and focuses on good laboratory practice, especially for small‑scale preparation and value assignment used by laboratories.

Key topics and technical requirements

• Applications of RMs/CRMs: Use in method validation, assessing precision and trueness, quality control, calibration, assigning values to other materials, and maintaining conventional scales (Clause 6 and Figure 1).
• Property values and uncertainty: Guidance on specification of measurands, uncertainty statements and propagation, and how CRM uncertainties contribute to measurement results (Clauses 6.2–6.4).
• Traceability requirements: Recommendations for establishing and documenting metrological traceability of property values to international standards where applicable (Clauses 6, 9–11).
• Handling and homogeneity: Practical handling, storage and homogeneity considerations for RMs/CRMs to maintain integrity during use (Clause 7).
• Precision and bias assessment: Procedures for assessing precision (replicate measurements, data treatment) and checking bias using CRMs or RMs (Clauses 8–9).
• Calibration models: Practical considerations and uncertainty models for calibrating instruments with RMs/CRMs (Clause 10 and Annex A).
• Assigning values and small‑scale RM preparation: Fundamentals for assigning values to materials and preparing calibrants on a laboratory scale (Clause 11). Large‑scale production and distribution are excluded.

Practical applications

ISO 33403:2024 is directly applicable to:

• Testing and calibration laboratories calibrating analytical instruments and establishing measurement traceability.
• Quality managers and technical assessors developing SOPs, quality control plans and validation protocols.
• Metrologists and analysts assigning values to in‑house materials or preparing small‑scale calibrants.
• Regulatory and accreditation bodies assessing laboratory competence with respect to RM/CRM usage.

Practical value includes improved measurement reliability, clearer uncertainty budgets, and documented traceability pathways when RMs/CRMs are used for calibration and method validation.

Related standards

• ISO 17034 - Requirements for producers of reference materials (large‑scale production and distribution).
• ISO 33405 - Reference materials - planning and production aspects.
• ISO Guide 30 and VIM (ISO/IEC Guide 99) - Terminology and concepts used throughout ISO 33403.

Keywords: ISO 33403:2024, reference materials, certified reference materials, RMs, CRMs, measurement traceability, calibration, uncertainty, precision, value assignment.