ISO 33408:2025

Overview

ISO 33408:2025 - Guidance for the production of pure inorganic substance certified reference materials (CRMs) provides targeted technical guidance for producing solid pure metal and crystalline salt CRMs in alignment with the general competence requirements of ISO 17034. The standard focuses on steps from production planning to final documentation for CRMs intended for direct calibration use or for preparing solution calibration CRMs. It emphasizes best practices for purity assessment, homogeneity, stability, and metrological traceability of certified purity values.

Key technical topics and requirements

ISO 33408:2025 covers practical production elements and quality requirements, including:

• Specification of the CRM and measurand
  • Define intended use, measurand, safety, and fitness for purpose.
• Production planning
  • Systematic workflow covering sourcing, testing, packaging, characterization, and documentation.
• Candidate material sourcing and verification
  • Verification of primary component (PC) identity and demonstration of adequate purity before certification.
• Measurement strategies and characterization
  • Recommended approaches for purity determination, use of multiple methods, and strategies to achieve target measurement uncertainty.
• Homogeneity assessment
  • Sampling strategies, minimum sample size, and experimental assessment to ensure batch uniformity.
• Stability assessment and monitoring
  • Identification of instability sources, repeated use stability, and ongoing stability monitoring.
• Packaging, storage and handling
  • Selection and treatment of containers, label requirements, and transport/storage conditions to preserve CRM integrity.
• Metrological traceability
  • Linking the certified property values to appropriate metrological references.
• Documentation
  • Preparation of RM documents and certification reports; includes informative annexes on analytical strategies and production examples.

Practical applications and target users

ISO 33408:2025 is intended for organizations and professionals involved in producing or using high-purity inorganic CRMs, including:

• Reference material producers (RMPs) and national metrology institutes
• Analytical and calibration laboratories establishing traceability and calibrating instruments
• Quality managers in industries that require ultra-high-purity metals and salts (e.g., electronics, semiconductors, advanced materials)
• Regulatory bodies and auditors assessing CRM production competence

Practical uses include calibration of measurement instrumentation, validation of analytical methods, and creation of solution calibration CRMs derived from solid-inorganic CRMs.

Related standards (selected)

• ISO 17034 - General requirements for competence of reference material producers
• ISO Guide 30, ISO/IEC Guide 99 (VIM), ISO/IEC 17000, ISO/IEC 9000, ISO 80000-9 - complementary vocabulary and metrology guidance
• ISO 33405 - referenced for broader production planning aspects

Keywords: ISO 33408:2025, pure inorganic substance certified reference materials, CRMs, purity assessment, homogeneity, stability, metrological traceability, ISO 17034, metal CRMs, crystalline salt CRMs.