ISO 33405:2024

Overview

ISO 33405:2024 - Reference materials: Approaches for characterization and assessment of homogeneity and stability provides practical guidance for the production and evaluation of reference materials (RMs). The standard explains concepts and approaches for assessing homogeneity, stability, characterization, uncertainty of certified values, and establishing metrological traceability. Guidance is intended to support implementation of ISO 17034; alternative approaches are acceptable provided ISO 17034 requirements are met. Note: brief guidance on commutability and qualitative properties is included, but multivariate quantities (e.g., spectral data) and detailed statistical methods for qualitative properties are excluded.

Key topics and technical requirements

• Homogeneity assessment

  • Need for experimental homogeneity studies and statistically valid sampling schemes
  • Study designs (basic single-run, randomized block, balanced nested) and sample-size considerations
  • Use of statistical power analysis, trend/outlier inspection, within-unit vs between-unit heterogeneity
  • Estimation of uncertainty contribution from homogeneity

• Stability assessment and monitoring

  • Types of instability and experimental approaches (real-time, isochronous, accelerated studies)
  • Selection of RM units, storage/treatment condition designs, handling of significant trends
  • Estimation of storage lifetime (shelf life) and uncertainty contribution from stability
  • Ongoing stability monitoring protocols and recommended monitoring intervals

• Characterization and value assignment

  • Use of reference measurement procedures, multi-laboratory characterization, and value transfer approaches
  • Establishing metrological traceability and verification of traceability chains
  • Consideration of sample preparation/pre-treatment effects on measurands
  • Evaluation and reporting of measurement uncertainty for certified values

• Scope limitations

  • Brief guidance for commutability assessment (no technical details)
  • Introductory guidance for some qualitative properties; detailed statistical methods for qualitative measurands are not covered
  • Not applicable to multivariate quantities such as spectral data

Practical applications

• Producing and certifying Certified Reference Materials (CRMs) and RMs used for calibration, method validation, and quality control
• Designing homogeneity and stability studies for RM manufacturers and metrology institutes
• Supporting accreditation and compliance with ISO 17034 for RM producers
• Informing uncertainty budgets for certified values used in laboratories, proficiency testing providers, and regulatory testing

Who should use this standard

• Reference material producers and manufacturers
• National metrology institutes and calibration laboratories
• Accreditation bodies and quality managers implementing ISO 17034
• Laboratories needing traceable calibration materials or method validation support

Related standards

• ISO 17034 - General requirements for the competence of reference material producers
• ISO 33406 - Additional information on production of RMs with qualitative property values
• ISO/IEC Guide 99 (VIM) - Vocabulary and reference for measurement concepts

For complete methodologies, study designs and statistical formulas, consult the full ISO 33405:2024 document.