ISO Guide 31:1981
(Main)Contents of certificates of reference materials
Contents of certificates of reference materials
Contenu des certificats des matériaux de référence
General Information
Relations
Standards Content (Sample)
IDE 31
First edition - 1981-09-15
Contents of certificates of reference
materials
UDC 53.089.68 : 381.822
Ref. No. ISO GUIDE31-1981 (E)
Descriptors
: reference materials, certification, documents, contents list.
Price based on 8 pages
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Foreword
.
ISO (the international Organization for Standardization) is a worldwide federation of
ii.
national Standards institutes (ISO member bedies). The work of developing lnter-
national Standards is carried out through ISO ’technical committees. Every member
body interested in a subject for which a technical committee has been set up has the
right to be represented onthat committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work.
ISO guides are intended essentially for internalluse in ISO committees or in some cases
for the guidance of member bodies when dealing with matters which would not nor-
mally be the subject of an International Standard.
ISO Guide 31 was drawn up by the Committee on reference materials (REMCO) and
was submitted directly to ISO Council who accepted it in August 1981.
0 International Organkation for Standardimtion, 1981 l
Printed in Switzerland
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GUIDE 31-1981 (E)
Contents of certificates of reference materials
0 Introduction
This document is an outcome of the collaboration of ISO Committee on reference materials (REMCO) with the following international
organizations :
EEC, IAEA, OIML, IUPAC and WHO. The first draft was prepared by Mr. T. W. Steele of the “National Institute for
Metallurgy (SASS) “.
Although the amount of information that is given on certificates of reference materials varies considerably, this Variation is only partly
accounted for by the varying nature of the material. Thus, certificates of even basically the same type of material issued by different
Producers vary from a bare Statement of the value of the certified property to a lengthy document containing very detailed informa-
tion, some of it not always relevant to the reference Sample. Some Producers do not issue certificates at all but expect the user to
search for the information in publications which may not be readily available.
This diversity in the Character of certificates has come about because the essential function of a certificate has not always been ap-
preciated. The true nature of a certificate tan best be appreciated if the cet-tificate is compared with two other sources of information
on a. reference material. These are the label and the repott : the former is normally affixed to the Sample Container, and the latter ac-
companies the certificate or tan be obtained on request.
Usually, because the size of the label is determined by the size of the Container to which it is to be affixed, the label tan contain only
the briefest of information about the reference material and, normally, simply identifies the reference material. The report on the
reference material usually contains all the relevant information including the details of the certification procedure. However, because it
is so detailed, there is clearly a need for a second document that would condense all the information about the Sample. This document
is the certificate which tan be described as the Synopsis of the report. A certificate that is expanded in an attempt to make it serve also
as a report defeats its purpose, and is no longer the concise and readily referenced document that it should be.
Traditionally, the certificate has consisted of one or two pages as though the need for a brief synoptic document has always been in-
tuitively felt to be appropriate. Apart from the desire for brevity, there was little need for a detailed certificate because the certified in-
formation was taken on trust. Except until comparatively recently, certified reference materials were produced by only a few specialist
organizations whose reputations were such that their names were a sufficient guarantee of the integrity of the reference material.
With the increase in the number of Producers this assumption is no longer acceptable because no matter how high the reputation of
the Producers in their scientific and technological fields, it does not follow that this reputation is necessarily transferable to the fledgl-
ing reference material. Parallel with the increase in the number of new Producers there has been a demand for a reference material of
higher quality, a consequence both of the increased precision of measuring equipment and the need for more accurate data in the
scientific and technological disciplines. In illustration of this trend, Producers freely admit that their old reference materials may not
meet the more stringent requirements of today. Whereas formerly it did not seem to be of much importante to know the bounds of
uncertainty of a certified value other than in some intuitive fashion, users are now becoming increasingly more critical of certificates
that do not give this information. The user needs not only this information but also the details of the whole certification procedure. In
other words, not only must the certified value be accurate but it must now be seen to be accurate. In recognition of this need, the
latest certificates of Producers of long-established reputation are becoming more detailed and sometimes take on the Character of a
repot-t. On the other hand, as has been mentioned, many of the younger Producers issue detailed reports without certificates. The cer-
tificate is thus in danger of losing its useful synoptic Character, or in some areas of becoming extinct. This eclipse of the certificate
per se is unfortunate, and appears to arise from the fact that the distinction between a cer-tificate and a report on the reference
material has not been clearly recognized.
In summary, a certificate should communicate information about a reference material from the Producer to the User; in essence, this
information is a Statement of the cet-tified property values, their meaning, and their confidence limits. 1) The remainder of the informa-
tion is peripheral to this central Statement and has two purposes : to describe the general nature and use of the material, and to assure
the user of its integrity. In a weil-prepared certificate, the information should be presented in a form that enables the user to draw his
own conclusions about the integrity of the certified material.
This Guide is help Producers to prepare clea r and concise certificates, which, while maintai ning the essential Character of
intended to
reference material.
a certificate, should help to provide, in summary form, all the information needed by the user of the
1) The term “un certainty” in place of “confidence limits” is sometimes preferred (sec ISO Guide 30).
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ISO GUIDE 31-1981 (E)
1 Scope and field of application
A series of headings is given in clause 2 to indicate the information that should be provided on a certificate. An explanation is given
under each heading, together with examples where more clarification seemed to be necessary. In the compilation of these headings,
the aim was to cover the required information on as wide a range of reference materials as possible, taking into account such diverse
examples as a triple-Point cell, a microscope magnification Standard, a powdered rock, and a biological material. Some of the
headings may not be needed for a particular material but these are likely to be the exception rather than the rule. The headings are
given in what seems to be a logical Order for the presentation of the information, which in summary is as follows : the general par-
ticulars of the certifying organization and the reference material [name, Sample, number, date of certificate, etc. (sec 2.1 to 2.10)]; a
description of the material and its intended use (sec 2.11 to 2.16); the certified values, their confidence limits, and an explanation of
these values and the techniques used for their measurement (sec 2.17 to 2.21); the references and the names of participating analysts
and certifying off icers (sec 2.22 to 2.25).
lt should be emphasized that this Guide is concerned with the informational contents of the cet-tificate and not its style or format.
Thus, the Order of headings and the wording of the headings may be changed to suit the reference material or the preferences of the
Producer.
2 Certificate headings
21 . Name and address of the certifying organization
This name (usually given in prominent type at the head of the certificate) should be that of the body or organization that accepts
responsibility for the information on the certificate. Cooperating Iaboratories or an organization that may only have prepared the sam-
ple are preferably given elsewhere (see 2.21).
2.2 Title of the document
There should be a distinct title. Common titles are
Certified reference material certifica te o f analysis
Certificate of a reference material
2.3 Status of the certificate
Some certificates are of a provisional nature, and this qualification when appropriate, should be clearly stated.
2.4 Name of material
As far as possible, the name should distinguish the type of reference material. Thus, “triple-Point cell, diphenyl ether” is preferable to
just “triple-Point cell ”. The name of the rock or ore followed by its locality or a compositional characteristic gives more individuality to
“Syenite (Phalaborwa)” or “Nepheline syenite ”. For metallurgical samples, it is appropriate to give
geological materials; for example,
the concentration of an important element, for example “Carbon steel 0,14 % “.
.
25 Sample number (and batch number)
Esch reference material should be numbered, the number preferably being accompanied by the initials of the certifying organization,
for example “BCS No. 260 ”. The practice adopted by the National Bureau of Standards of following the number with a letter (a to z)
to identify a renewal of the original material is recommendable.
2.6 Date of certification
In addition to the original date of certification, the dates of all revisions should be given.
2.7 Availability of other forms or sizes of the reference material
in relation to the material named on the certificate. Thus, th ere ca n be one or more packaged
This information need be given only
ble in the form
units supplied or, as frequently happ ens with meta Ilurgical sam ples, a metal or alloy may be availa of Chips and discs.
2
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ISO GUIDE 31-1981 (E)
28 . Source of the reference material
A knowledge of the origin or Source of the material constituing the reference material could be useful background information for the
User. The geographical location of a rock Sample, for example, is of special interest to geologists and geochemists. On the other hand,
the supplier may not wish to have the composition of his material identified since it might reveal confidential information on his com-
mercial material.
.
29 Supplier of the reference material
material tan be obtained should be given if the certifying
The name and address of the organization from whom the reference
orga niza tion is
not the supplier
2.10 Preparer of the material
The preparation of the material might be undertaken by an organization other than that which undertook the testing and certification.
The comminution of ores, the melting and casting of metals, the manufacture of chemicals, and the fabrication of equipment that is
an integral par-t of the reference material, are all important Parts of the production of a reference material and tan have a vital bearing
on the homogeneity and stability of the material. The organization that undertakes this work should therefore be given this recogni-
tion.
2.11 Description of the reference material
The general description of the material should, in effect, amount to a detailed explanation of the name of the material, for example
“The triple-Point cell contains approximately 150 g of highly purified phenoxylbenzene and has been evacuated of air before sealing.”
For a biological material, part of the description could be “The material has been preserved with benzoic acid ”. For compositional
material, there could be a description of the main constituents that do not appear in the table of certified values, and for geological
material, the mineral composition could be given.
A description of Ehe physical Character of the material is also appropriate under this heading.
Examples :
“This reference material is in the form of discs 31 mm in diameter and 14 mm thick”
“The reference material consists of three filters in special holders”
-
“The material has been ground to pass a 200-mesh sieve”
-
“The Sample of gas is supplied in a steel cylinder at 12,4 MN/m2 pressure”
Toxic or hazardous (for example radi oactive) ingredients in the material should be mentioned and, if circumstances Warrant it, a warn-
ing shou ld be given in bold type
2.12 Intended use
The purpose for which the reference material was issued should, as far as possible, be clearly stated so that it is not misused. For ex-
ample, a reference material of a mineral may be suitable for methods of analysis that require a relatively large mass of subsample but
would be totally unsatisfactory as a reference material for the electron-microprobe technique.
The following are examples of entries appropriate to this heading :
-
“The reference material is intended for the calibration of the magnification scale of a scanning electron microscope to an ac-
curacy of 5 % within the range of 1 000 to 200 000 magnifications”
-
“lntended for the reali zation of a fixed temperature Point on the practical temperature scale and, therefore, for the calibration
of temperature measuring equipment”
“A reference material intended for the following :
a) for calibration of instruments for determining the concentration of precious metals in ore samples;
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ISO GUIDE 31-1981 (E)
as an arbitration Sample for commercial transactions;
b)
for the verification of analytical methods for precious metals;
Cl
for the preparation of secondary reference materials of similar composition.”
d)
2.13 Stability, transportation, and storage instructions
As the reference material (and, therefore, the certified values) tan be affected by numerous factors such as temperature, light, and
exposure to the atmosphere, a description should be given of the conditions of transportation, handling, and storage that are most
favourable to the maximum lifespan of the Sample.
Wherever possi ble, the period of validity of the reference ma terial should be sta ted. When the stability is suspect but known exactly, a
statement such as the following would at least introduce a cautionary note :
“lt is possible that ageing of the glass may Cause the filters to Change transmittance by about 1 % over a period of approximately
1 year. Tests have shown that, in a normal laboratory atmosphere (absence of direct sunlight and temperatures of 10 to 30 OC),
the Sample is stable for 1 year. The purchaser will be notified if deterioratio
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