ISO 33408:2025

Guidance for the production of pure inorganic substance certified reference materials

This document gives specific technical guidance for the production of pure metals or their corresponding crystalline salt certified reference materials (CRMs) in accordance with the general requirements of ISO 17034. This document is only applicable to solid pure metal and crystalline salt CRMs, including candidate materials, unless otherwise noted.

Recommandations pour la production des matériaux de référence certifiés pour des substances inorganiques pures

General Information

• Status: Published
• Publication Date: 23-Oct-2025
• ICS: 77.020 - Production of metals
• Technical Committee: ISO/TC 334 - Reference materials
• Drafting Committee: ISO/TC 334 - Reference materials
• Current Stage: 6060 - International Standard published
• Start Date: 24-Oct-2025
• Due Date: 16-Aug-2025
• Completion Date: 24-Oct-2025

Standards Content (Sample)

International
Standard
ISO 33408
First edition
Guidance for the production of
2025-10
pure inorganic substance certified
reference materials
Recommandations pour la production des matériaux de référence
certifiés pour des substances inorganiques pures
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Technical and production requirements . 2
4.1 General .2
4.2 Production planning .2
4.3 Specification of the CRM and its measurand .2
4.3.1 General .2
4.3.2 Classes of inorganic purity reference materials .3
4.3.3 Intended use of the CRM .3
4.3.4 Specification of the measurand .3
4.3.5 Metrological reference .4
4.3.6 Fitness for purpose .4
4.3.7 Safety considerations .4
4.3.8 Resources and approaches to purity analysis .4
4.4 Candidate material sourcing and assessment of suitability, including verification of PC
identity and adequate purity .5
4.4.1 Material sourcing .5
4.4.2 Verification of PC identity .5
4.4.3 Material suitability .6
4.5 Product packaging and specification of conditions for storage and safe handling .6
4.5.1 General considerations .6
4.5.2 Selection and treatment of packaging materials .6
4.5.3 Storage and transport.6
4.5.4 Container Labels .7
4.6 Measurement strategies for assessment of purity .7
4.7 Development and validation of procedures for characterization, including achieving
target measurement uncertainty .8
4.7.1 General .8
4.7.2 Use of Multiple methods for purity determination .8
4.7.3 Property value boundaries .8
4.8 Assessment of homogeneity .9
4.8.1 General .9
4.8.2 Preliminary assessment of homogeneity .9
4.8.3 Sampling strategy .9
4.8.4 Minimum sample size .9
4.8.5 Experimental method of homogeneity assessment .9
4.9 Assessment and monitoring of stability .10
4.9.1 General .10
4.9.2 Sources of instability .10
4.9.3 Repeated use stability .10
4.9.4 Stability monitoring .10
4.10 Characterization of the CRM .11
4.10.1 General .11
4.10.2 Direct determination .11
4.10.3 Indirect determination .11
4.11 Metrological traceability of the certified property value . 13
4.12 Preparation of RM documents . 13
Annex A (informative) Analytical strategies for purity characterization . 14
Annex B (informative) Examples of production and certification of pure substance inorganic
certified reference materials .32

iii
Bibliography .52

iv
Foreword
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v
Introduction
Reference materials (RMs) play an important role in measurement processes and support sound, widely
recognized measurement systems. ISO 17034 specifies general requirements to be met by reference material
producers (RMPs), including for the production of certified reference materials (CRMs). CRMs play a key
role in ensuring that measurements are comparable across time and space and are used by laboratories to
establish metrological traceability of their measurement results to appropriate references.
This document outlines recommendations conforming to the general requirements of ISO 17034 for
production of pure metal or their corresponding crystalline salt CRMs intended for direct use for calibration
of appropriate measurement instrumentation or subsequent preparation of solution calibration CRMs.
Technical guidance is provided on key aspects of the production of such CRMs, including assessment of
their homogeneity and stability as well as recommended approaches for characterization and assignment of
certified purity values.
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