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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Published in Switzerland
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 terms and definitions
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO Guide 30, ISO/IEC Guide 99 and
ISO 3534-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Overview of preparation of candidate reference materials (RMs)
Many RMs and CRMs are produced by RMPs and are commercially available. However, laboratories
conducting routine tests frequently encounter difficulties in acquiring matched matrix RMs that possess
a comparable matrix and analyte content level, or even just one of these aspects. In cases where matched
matrix RMs are challenging to obtain from the market, the capability to prepare samples closely matched to
those used in routine tests becomes crucial.
For such RM users, the preparation of homogeneous and stable materials prior to conducting assessment of
homogeneity and stability is crucial. If the preparation steps are inadequate to ensure a sufficient level of
homogeneity and stability, the material will not be suitable for the intended use. Therefore, the preparation
of any candidate RM requires a level of technical and organizational competence. It is acknowledged that in

many cases the candidate RMs are prepared by technically competent staff that are knowledgeable about
the materials and processes being used.
This document focusses on the steps involved with the preparation of RMs. The key steps involved in the
production of a matrix RM are summarized in the flow chart in Figure 1 and are described in more detail in
References [12] and [13].
The following clauses offer detailed information on material specification (Clause 5), sourcing and selection
of bulk material (Clause 6) and material processing (Clause 7). More guidance on the rest of the production
steps, which includes the characterization, as well as the assessment of homogeneity and stability is covered
in ISO 33405. Any requirements for the production of RMs can be found in ISO 17034.
Materials can be sourced from, and processed by third parties, where they have specialized equipment
and/or expertise. Materials can even be products that are commercially available and meet the user’s
specifications (e.g., food products available in appropriately sized units from a single production batch).
Figure 1 — Key steps in the production of RMs. This document focusses on the steps for the
preparation of an RM (blocks with a solid black outline).
5 Material specification
5.1 General
The specification of a candidate matrix RM is a crucial consideration. The intended use, including the
acceptable level of uncertainty for the measurement or test results, is an important consideration for
both the production and use of all RMs. Key criteria include similarity to real samples and availability in
appropriate quantities. In practice, the impetus for the preparation of such candidate RMs can often be the
fact that adequate matrix RMs are not available. Therefore, the specific matrix and property combination for
the test sample in question are likely to be used, and matching is not an issue for laboratories.
5.2 Matrix type and matching
In general terms, the uncertainties associated with a measurement result from a homogeneous sample arise
from the two main stages of the measurement procedure:
— the preparation of a sample comprising digestion, extraction, clean-up, etc.;
— the measurement of the property in the prepared sample by a suitable technique.
The key criteria in the specification and selection of an RM are therefore for the material to be as similar as
possible to real samples and available in appropriate quantities.

The matrix of the RM needs to be the same or as similar as possible to the matrix of the routine test samples,
so that a satisfactory result for the RM is genuinely indicative of satisfactory results for the test samples.
This matrix matching requires some knowledge of the analytical procedure used on the routine samples, so
that a judgment can be made as to the degree of variation of the physical/chemical properties of the sample
and test matrices that can cause them to respond differently to a particular measurement procedure. For
example, a freeze-dried food matrix can behave differently during analysis to a similar foodstuff with higher
moisture content.
[14]
Commutability has particular significance in clinical chemistry and has been described elsewhere .
5.3 Properties and property values
For all RMs, the properties of a candidate matrix RM are crucial for its intended use in measuring routine
test samples.
When the material is employed to verify quantitative measurement results, having a property value close to
the mean value of typical test samples or values near the decision limit for the application becomes crucial.
This can be verified through preliminary screening measurements on several candidate source materials to
ensure the selection of the most appropriate one.
In situations where an RM is used for the statistical control of a measurement method using a quality control
chart, the important characteristic of the RM is that its matrix is closely resembling that of the test sample.
For drift monitoring, the important characteristics of the RM include stability and the ability to provide
a measured signal that minimizes counting statistical uncertainty. An optimal drift monitor material can
have a higher concentration of the measurand compared to the test sample.
5.4 Unit size
Unit size is the amount of material that comprises a single unit of the RM. When preparing a candidate
RM, the size of individual units is based on the likely use, i.e., the amount of material needed for the
measurements concerned and whether the units are to contain sufficient material for a single analysis or
multiple measurements.
5.5 Total bulk amount of material
An estimate is needed of the total bulk amount of candidate matrix RM that needs to be sourced. In principle,
this can be estimated by considering:
— the expected number of units needed for the lifetime of the material;
— the expected number of units needed for homogeneity and stability testing and characterization (as
applicable);
— the unit size;
— the preparation yield;
— the quantity of material that can readily be homogenized;
— the assumed stability of the material;
— the type and size of the storage facility.
6 Sourcing and selection of bulk material
Sourcing of bulk materials for RM production can at first seem difficult, especially in those cases where
large quantities of material are needed. However, there are several options that are available including:
— leftover sample material from testing activities;

— accurate gravimetric formulation.
Processing the bulk material can have significant cost implications for the production of RMs and simple,
straightforward processing methods need to be used to ensure cost-effective RM production. The sourcing
of the material usually considers the difficulty and cost implications of the processing of the material. The
exact preparation procedures to be followed for a particular RM will depend on the nature of the matrix and
the properties of interest.
In general, liquid matrix RMs are much easier to produce than their solid counterparts. The main reason for
this is that homogeneous liquids can easily be achieved even with rudimentary equipment (e.g., large mixing
containers equipped with paddles or magnetic stirrers). A liquid is easily spiked, filtered, or mixed with
additives and stabilizers. The corresponding processes for solid materials, milling, grinding, mixing, and
sieving are much more difficult to accomplish homogeneously, especially for quantities greater than 20 kg.
These techniques require a significant investment in major capital equipment when large-scale preparation
is envisaged.
When sourcing biological materials for example, for control of measurement procedures for medical
laboratories, the following specific issues need to be considered:
— ethics of the retention and use of residual patients’ samples for the production of RMs;
— legal liabilities of retention and use of residual patients’ samples purchased for the production of RMs;
— medical laboratories creating RMs need to have a high degree of confidence in the identity of the material
selected, to avoid use of misidentified organisms;
— materials sourced for RM production are screened for potential risks including health hazards, especially
if the processing includes the use of contaminated sharps or has the potential for aerosol formation.
7 Material processing
7.1 General
Once the bulk material has been sourced for the candidate matrix RM, there are several processing stages
that need to be carried out to ensure the candidate matrix RM has the appropriate homogeneity and stability
for its intended use. Take care to ensure consistency in processing across multiple days. Some of the more
common processes are described in 7.2 to 7.10.
7.2 Avoidance of contamination
For all candidate matrix RMs, it is important to prevent contamination by substances which can
potentially interfere with the intended measurement process (e.g., a similar material or contamination of
a blank material). Hence, all containers are carefully cleaned and dried before filling to remove possible
contaminants.
In addition, consideration needs to be given to the possible interaction of bulk material with processing
equipment and/or leaching of contaminants/impurities from the processing equipment parts, or the
container, into the bulk material.
7.3 Drying
Removal of water makes candidate matrix RMs far easier to handle and improves both their transportation
and long-term stability. Drying of soils and similar matrices is carried out at ambient or elevated
temperatures, depending on the properties of interest, since the more volatile components could be partly
lost at higher temperatures. Water removal also reduces the likelihood of microbial growth formation,
which is a particular problem with biological materials. Freeze-drying is a technique which is useful with
temperature sensitive properties or matrices.

7.4 Milling and grinding
For solids, some form of crushing, milling, grinding and particle size reduction is often necessary to ensure
uniform particle size and to improve homogeneity of the candidate matrix RM. For large quantities, these
processes are slow and can take several days to complete. Take care not to introduce contamination from
the apparatus during the grinding process. The health and safety aspects of grinding large quantities of
particulate matter, which could have toxic components, needs to also be considered. Cryogenic grinding at
−78 °C (solid CO ) or −196 °C (liquid N ) could be necessary for polymers, biological, oily/fatty, and thermally
2 2
labile materials.
Specialised equipment can allow producing a material with a smaller particle size than laboratory samples,
which can lead to changed extraction or digestion behaviours. This can result in the reference material not
being representative of the real sample anymore. It is therefore important to ensure that also the particle
size of the RM is representative for real samples.
7.5 Sieving
Sieving is often carried out after milling and grinding to improve the homogeneity of the candidate matrix
RM. Particulate materials such as soils, ores, ashes, and ground biological materials are passed through a
standard sieve to remove large particles that are above a prescribed size.
Sieving, however, changes the matrix composition. If a large fraction is removed by sieving, the analyte
concentration can change, and the matrix can no longer reflect the composition of regular test samples.
7.6 Mixing and blending
When the candidate matrix RM is in solid form, it is homogenized by thorough mixing, using for example a
roll-mixer, shaker, or end-over-end mixer. Such mixing is carried out after milling, grinding, and sieving.
Blending of two or more materials with sufficiently similar matrix compositions and differing property
values can enable the production of RMs with a desired property value, a set of similar RMs covering a range
of property values, or the production of RMs from an existing RM.
To obtain homogeneous mixtures, the materials to be mixed need to have similar densities and particle size
distributions.
7.7 Filtration
Filtration of solutions before bottling removes any particulate and fibrous solids that would compromise the
homogeneity of the bulk candidate matrix RM. However, some liquids cannot be filtered due to:
a) viscosity;
b) potential loss of active ingredients by adsorption to the filter;
c) the introduction of contamination. Qualification of the filter is critical to avoiding loss of active
ingredients.
Typically, liquids such as waters and leachates, are filtered through a 0,45 µm filter prior to bottling or
ampouling.
7.8 Stabilization
Certain analytes in the candidate matrix RM are unstable and therefore need to be stabilized at the bulk
stage of the preparation procedure. Metals, for example, can precipitate out of neutral or alkaline solutions
because of hydrolysis or oxidation, and adjustment of the pH of the solution to below 2 counteracts this
−1
problem. Copper at a concentration of 1 mg·l has been used to counteract algal growth in aqueous solutions.
Different materials can require other approaches such as addition of antioxidants, preservatives, texture
stabilizers, etc.
7.9 Sterilization
Prepared soils, sewage sludges, and biological materials can contain persistent pathogens that are potentially
harmful to humans. They can also contain spores that cause fungal moulds to develop on storage, which
could initiate changes in either the composition of the bulk material or the individual units. Such organisms
need to be destroyed before the final units are prepared and packaged.
Before sterilizing any candidate matrix RMs, it is important to consider the impact of the proposed
sterilization process on the properties of interest and/or the matrix, particularly those which degrade at
elevated temperatures.
Autoclaving is an inexpensive and convenient means of sterilization that can be used for materials that are
temperature resistant, for example, metals in sediments. Autoclaving can be done on the bulk material prior
to final homogenization and unit preparation or on the final samples. However, it is important to ensure that
the core of the material reaches 121 °C.
Irradiation can be used on the final packaged units (e.g., ampoules, bottles, or pouches). Gamma irradiation
is a convenient means of sterilization at ambient temperature so changes in matrix composition are less
likely than with autoclaving. Dose values need to be determined such that they are effective in removing
pathogens but do not adversely affect the material by, for example, raising the temperature to unacceptable
levels (e.g., chocolate). However, gamma irradiation is beyond the means of most laboratories, requiring
specialist subcontractors.
Sterilization is performed after subdivision and packaging has been completed, and the material is in its
final packaged form, otherwise the material will not be sterile.
7.10 Subdivision and packaging
7.10.1 General
The last steps of the material processing are subdivision and packaging. Subclauses 7.2 and 7.3 describe
some of the key considerations for the subdivision process and choice of containers to ensure the RMs are
sufficiently homogeneous and stable for their intended use.
Some candidate matrix RMs are used as bulk materials and do not need to be packaged into individual units.
In-house reference materials are often not distributed and are therefore not always packaged into units, but
subsamples are taken from the bulk prepared material as and when needed.
7.10.2 Choice of containers
For RMs to be prepared cost-effectively, one aspect that needs careful consideration is the choice of
appropriate containers for the individual units. If unsuitable containers are used, the material could quickly
degrade. The type of container used depends on the inherent stability of the material and the length of time
it is expected to remain stable. For particularly susceptible materials, two layers of containment (e.g., a vial
within a polyethylene bag) can provide additional protection against degradation and contamination.
The following examples serve to illustrate the need for careful consideration of the container and its closure.
— Materials can either lose or pick up moisture if the container is not securely closed. Glass containers with
1)
screwcaps fitted with “polycone” inserts are preferable to simple screw caps. Sealed cans, foil pouches,
or septum-lined crimp-top vials offer more security.
— Oxygen sensitive materials need to be prepared and sub-sampled under an inert gas atmosphere
(nitrogen or argon).
— For aqueous samples containing low concentrations of metals (e.g., mg/kg or below), glass containers are
not recommended because of possible adsorption of the metals onto the walls over time. High-density
polyethylene (HDPE) bottles with screwcaps are more suitable for this application but have the potential
1) Polycone liners are cone-shaped polyethylene cap liners that provide a better seal than simple wadded cap closure.

problem of loss of water by evaporation through the bottle walls. This can be minimized by storage in a
refrigerator (rather than at ambient temperature) or using fluorine-treated polyethylene bottles.
— The possibility of contamination of the RM by the leaching of impurities from the container also needs to
be considered. For example, the iron content of canned foodstuff RMs could be subject to unpredictable
increases on a can-by-can basis, as iron leaches from the can wall into the food matrix. Bottles (whether glass
or HDPE) containing aqueous acid solutions could also give rise to leaching problems. As a rule, containers
that can interact with the RM need to be carefully evaluated before use by suitable leaching trials.
— For relatively inert matrices, such as soils and other dried environmental or biological materials, screw-
cap glass jars are usually satisfactory. Amber glass gives additional protection against degradation
induced by light.
— RMs comprising relatively volatile components susceptible to evaporation, such as some organic
solvents, will normally require a septum-lined crimp-top, glass vial, or flame-sealed glass ampoules. It is
preferable for vials and ampoules to be amber to reduce the impact of light.
Some preliminary experimental work, including blank and stability studies, can be necessary to identify the
most suitable container type to use for a particular RM.
If the unit size is larger than the sample size taken for a measurement, then consideration must be given
to the stability of the material for reuse according to the requirements of ISO 17034. The effect of repeated
opening and closing of the sample containers is also assessed if repeated use of the material is anticipated.
If a material is unlikely to be stable once opened, then it is preferable to restrict the unit size to a single use
portion.
Tamper evident closures need to be considered if the unit is only intended to be used once.
7.11 Subdivision procedures
Once a homogeneous bulk candidate matrix RM has been produced, the essential requirement of any
subdivision process is that the homogeneity of the material is maintained. Ensure that the sub-division
process itself, or the time taken to complete the subdivision of bulk material, does not re-introduce
heterogeneity into the material. This could conceivably occur in several ways.
Matrices comprised of mixtures of liquids of differing volatilities (e.g., ethanol in water) can undergo
selective evaporation of one component during a prolonged subdivision run, causing a rising or falling
trend in property value from the first to the last units produced. Effects of this sort can be minimized by
protecting the bulk material from evaporation and by completing the subdivision in as short a time as is
consistent with accurate dispensing.
All liquids and solutions need to be stirred continuously while individual aliquots are being dispensed.
Solutions need to be filtered before dispensing commences if particulates are likely to be present to an
extent that could affect the properties of interest.
Take care with solid particulate matrices such as soils, sediments, industrial products, etc. to ensure
that segregation of finer particles does not occur during subdivision. Take special care when sampling
bulk material from a large drum, to ensure that there is no vertical segregation. Riffling is a process for
representatively subdividing free-flowing powdered materials so that each aliquot receives similar
particulate fractions. When operated effectively, riffling minimizes flow segregation and produces units
with a low between-unit variation. Commercial riffling devices can be used to subdivide such materials
without introducing heterogeneity. Sampling and subdivision of particulate materials are described in more
[15]
detail in ISO 14488 .
In food matrices with a high fat content (e.g., mackerel paste), there could be a tendency for the fat to separate
as a discrete phase. If such effects occur, the matrix needs to be stirred continuously during dispensing and/
or additives included in the matrix to slow down the separation process.
As a general principle, subdivision of a bulk material is completed as quickly as possible to minimize
the opportunities for the matrix to revert to heterogeneity. Where appropriate, take steps to maintain a
homogeneous bulk material during the subdivision process. It could be necessary to discard the first and/or

last portions dispensed from the bulk material, especially of complex matrices that are especially prone to
segregation effects.
In the case of RMs intended for trace analysis, take special care not to introduce additional impurities (e.g.,
from the air, apparatus, laboratory vessels, etc.) during subdivision of the material as this could change the
property value being measured.

Annex A
(informative)
Case study 1 — Production of a quality control material (QCM)
2)
from coal
A.1 Objective
A coal testing laboratory uses a quality control material (QCM) for daily quality control for proximate and
ultimate analysis in accordance with the applicable ISO standards. One can of 1 L, holding approximately
1 kg coal, is sufficient for checking the analysis results for a week. The laboratory would like to use the
material for one year and calculates that it needs 100 kg of starting material. The starting material, as
delivered, is 50 mm in top size.
The laboratory is interested in a QCM that represents blended coal of the type used in power plants.
A.2 Sampling
The samples are mechanically removed from a conveyor belt, crushed, and sieved to a top size of 10 mm
and split into 6 portions of 10 kg per sample. In total, 12 samples are taken from the blend. The laboratory
receives 12 plastic bags, each containing 10 kg of blended coal.
A.3 Checking the suitability of the material
The laboratory takes a sample from one of the bags and prepares it for analysis. It determines the volatile
matter, and ash contents, gross calorific value (proximate analysis), as well as the contents of carbon,
hydrogen, nitrogen, and sulfur (elemental analysis). These results confirm the suitability of the material
with respect to the content levels and calorific value.
A.4 Sample preparation
The coal is dried in air at ambient temperature to remove the excess water, sieved, split into 10 portions, and
subdivided.
For the subdivision, a laboratory riffler is used with 10 tubes. To eliminate possible differences between the
bags, the subdivision scheme shown in Table A.1 is used.
2) This case study was provided by Adriaan M.H. van der Veen, NMi Van Swinden Laboratorium (VSL) B.V., Thijsseweg
11, 2629 JA Delft, The Netherlands. Subclauses A.1 to A.4 focus on the preparation of the RM.

Table A.1 — Subdivision scheme
01 02 03 04 05 06 07 08 09 10
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
01.01 02.02 03.03 04.04 05.05 06.06 07.07 08.08 09.09 10.10 → A
01.02 02.03 03.04 04.05 05.06 06.07 07.08 08.09 09.10 10.01 → B
01.03 02.04 03.05 04.06 05.07 06.08 07.09 08.10 09.01 10.02 → C
01.04 02.05 03.06 04.07 05.08 06.09 07.10 08.01 09.02 10.03 → D
01.05 02.06 03.07 04.08 05.09 06.10 07.01 08.02 09.03 10.04 → E
01.06 02.07 03.08 04.09 05.10 06.01 07.02 08.03 09.04 10.05 → F
01.07 02.08 03.09 04.10 05.01 06.02 07.03 08.04 09.05 10.06 → G
01.08 02.09 03.10 04.01 05.02 06.03 07.04 08.05 09.06 10.07 → H
01.09 02.10 03.01 04.02 05.03 06.04 07.05 08.06 09.07 10.08 → I
01.10 02.01 03.02 04.03 05.04 06.05 07.06 08.07 09.08 10.09 → J
Starting with the 10 bags (top row), 100 subsamples are made by dynamic riffling. The numbering of the
subsamples reveals the sample from which it is subdivided (first pair of digits) and from which tube of the
riffler it stems (second pair of digits). The subsamples are combined in such a fashion, that each composite
sample A through J contains one subsample from each bag and one subsample from each tube of the dynamic
riffler.
In a second step, the 10 composite samples A to J are riffled again to give 100 samples. The samples are put
into small plastic bags in cans. From 10 cans, chosen at random, 2 subsamples are taken for a homogeneity
test. The samples for the between-bottle homogeneity study are analysed for moisture and ash content, and
gross calorific value.
The cans containing the 100 samples are closed and labelled with the date of blending, and the sequence
number obtained from the second sub-sampling. Composite sample A delivered cans 1 to 10, and so on. The
laboratory considers preservation of the history from the sample production essential to support a root
cause analysis if needed later.
A.5 Between-bottle homogeneity study
The between-bottle homogeneity study is carried out with two replicates on 10 cans from the batch of 100.
[22]
One-way analysis of variance is used to determine the between-bottle standard deviation . Previous
experience has shown that for the selected parameters (ash content and gross calorific value) the between-
bottle standard deviation needs to be smaller than the repeatability standard deviation of the tests. For
both parameters, this objective is achieved in the homogeneity study.
A.6 Characterization
The laboratory monitors its quality using a Shewhart chart. The standard deviation is taken from a previous
chart from a similar blend. The mean value is obtained from 10 measurements from one can, taken over
10 consecutive days. On days 1 and 10, a CRM was analysed as well to confirm the laboratory results. The
QCM was used with the mean from these 10 measurements, after carefully scrutinizing the data. The data
analysis indicated no irregularities.

Annex B
(informative)
Case study 2 — Production of geological or metallurgical quality
3)
control materials (QCMs)
B.1 General
The materials produced include various geological or metallurgical particulate materials sourced from
customers of the analytical facility (matrix matched), typically in the order of 600 kg each. This includes, but
is not restricted to, ores, concentrates, feeds, tails, slags, and un-mineralized rock, soils, or sediments.
B.2 Project initiation
The need for RM production generally stems from the difficulty in sourcing a suitable commercial RM for
the analysis of a material of a unique sample matrix.
B.3 Sourcing of material
The following factors are considered.
— The matrix of the material to be as close as practically possible to the samples for which it will be used
as a quality control. By mixing mineralized ore with barren material/ lower grade ore of similar overall
composition, materials of different grades and a predetermined matrix can be manufactured. Once the
material is of the requisite composition it can be prepared into one homogenous bulk RM.
— Materials are stored and prepared in separate facilities according to their grade to prevent cross
contamination. Precious metal concentrates can require additional safekeeping procedures.
— The quantity of material needs to be sufficient to last for the duration o
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