ISO/TR 33402:2025

Technical
Report
ISO/TR 33402
First edition
Good practice in reference material
2025-01
preparation
Bonne pratique pour la préparation des matériaux de référence
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview of preparation of candidate reference materials (RMs) . 1
5 Material specification . 2
5.1 General .2
5.2 Matrix type and matching .2
5.3 Properties and property values .3
5.4 Unit size .3
5.5 Total bulk amount of material .3
6 Sourcing and selection of bulk material . 3
7 Material processing . 4
7.1 General .4
7.2 Avoidance of contamination .4
7.3 Drying .4
7.4 Milling and grinding .5
7.5 Sieving .5
7.6 Mixing and blending .5
7.7 Filtration .5
7.8 Stabilization .5
7.9 Sterilization .6
7.10 Subdivision and packaging .6
7.10.1 General .6
7.10.2 Choice of containers .6
7.11 Subdivision procedures .7
Annex A (informative) Case study 1 — Production of a quality control material (QCM) from coal . 9
Annex B (informative) Case study 2 — Production of geological or metallurgical quality control
materials (QCMs) .11
Annex C (informative) Case study 3 — Production of a wheat flour fortified with folic acid
quality control material (QCM) .18
Annex D (informative) Case study 4 — Bauxite quality control material (QCM) .24
Annex E (informative) Case study 5 — Pharmaceutical reference standards .29
Annex F (informative) Case study 6 — Production of testing materials for “bromate in water” .34
Bibliography .40

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 334, Reference materials.
This first edition of ISO/TR 33402 cancels and replaces ISO Guide 80:2014, which has been technically
revised.
The main changes are as follows:
— this document provides guidance for the preparation of reference materials and does not include
information about characterization or the assessment of homogeneity and stability;
— the scope of this document has been broadened to include all types of matrix reference materials and not
only reference materials used for statistical quality control.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Reference materials (RMs) are widely used in measurement laboratories for a variety of purposes, and it
is important to ensure that the material most appropriate for a particular application is used. Certified
reference materials (CRMs), i.e. those which have at least one certified value with associated uncertainty
assigned by a metrologically valid procedure, are primarily used for method validation and calibrations
providing metrological traceability.
While many RMs do not require characterization by metrologically valid procedures, they can be prepared
to meet specific measurement requirements, including quality control. The key requirements for these RMs
are sufficient homogeneity and stability, with respect to specific properties, for the intended use. Proper
preparation processes can ensure the material's homogeneity and stability.
This document provides general information on key steps in material preparation of candidate matrix RMs.
It is intended for laboratory staff involved in preparing and using matrix materials for specific applications.
Reference material producers (RMPs) can also use it as an information source for the preparation steps of
RM production.
The document includes case studies highlighting key considerations in RM preparation. Most of the case
studies describe the production of matrix RMs used for statistical quality control and include information
about the preparation of the materials as well as additional information about the characterization of the
property values and the assessment of homogeneity and stability, as applicable.
The general requirements for the competence of reference material producers (RMPs) are outlined in
ISO 17034, specifying necessary sample preparation steps. ISO 33405 covers guidance for assessing
homogeneity and stability, characterization, and value assignment of property values. ISO 33403 provides
guidance for the correct use of RMs. The requirements and guidance in these documents rely on the
competent preparation of the candidate RM. However, preparation steps, especially for candidate matrix
RMs, are intricate, and there is a lack of guidance focusing on these steps.

v
Technical Report ISO/TR 33402:2025(en)
Good practice in reference material preparation
1 Scope
This document gives general information on the key steps for the preparation of candidate matrix reference
materials (RMs) including the material specification, sourcing and selection of bulk material, and the
processing of the material, which are important steps for the production of matrix RMs.
The document provides information on the preparation of candidate RMs for laboratory staff who prepare
and use matrix materials for their specific applications. This document can also be used by reference
material producers (RMPs) as an information source for the preparation of the RMs that they produce.
This document also offers examples of specific case studies covering the preparation of matrix RMs in
different fields of application (see Annexes A to F). These are not complete "production manuals" but
highlight key considerations for the preparation steps of RMs.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO Guide 30, Reference materials — Selected t
...