SIST-TS ISO/TS 7821:2008

Tobacco and tobacco products - Preparation and constitution of identical samples from the same lot for collaborative studies for the evaluation of test methods

This Technical Specification provides a practical framework for the operations of dividing a lot (not necessarily homogeneous) of tobacco or tobacco products into several similar samples intended for collaborative studies, either within or between laboratories.

Tabac et produits du tabac — Préparation et constitution d'échantillons identiques à partir d'un même lot pour la conduite d'essais comparatifs portant sur la qualité des méthodes d'essai

L'ISO/TS 7821:2005 fournit un cadre pratique aux opérations de division de lot (pas nécessairement homogène) de tabac ou de produits du tabac en plusieurs échantillons similaires destinés à des essais comparatifs de laboratoire ou interlaboratoires.

Tobak - Priprava identičnih vzorcev iz iste serije (dobra praksa za primerljive študije izračunskih metod preskusov)

General Information

• Status: Published
• Public Enquiry End Date: 30-Jun-2008
• Publication Date: 28-May-2008
• ICS: 65.160 - Tobacco, tobacco products and related equipment
• Technical Committee: TIT - Tobaco and tobaco products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 23-May-2008
• Due Date: 28-May-2008
• Completion Date: 29-May-2008
• Ref Project: ISO/TS 7821:2005 - Tobacco and tobacco products — Preparation and constitution of identical samples from the same lot for collaborative studies for the evaluation of test methods

Relations

• Replaces: SIST ISO/TR 7821:1995 - Tobacco -- Preparation and constitution of identical samples from the same lot (Code of practice, for collaborative studies for evaluating methods of test)
• Effective Date: 01-Jul-2008

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 7821
First edition
2005-02-15

Tobacco and tobacco products —
Preparation and constitution of identical
samples from the same lot for
collaborative studies for the evaluation of
test methods
Tabac et produits du tabac — Préparation et constitution d'échantillons
identiques à partir d'un même lot pour la conduite d'essais comparatifs
portant sur la qualité des méthodes d'essai




Reference number
ISO/TS 7821:2005(E)
©
ISO 2005

---------------------- Page: 1 ----------------------
ISO/TS 7821:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


©  ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2005 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TS 7821:2005(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
 an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
 an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TS 7821 was prepared by Technical Committee ISO/TC 126, Tobacco and tobacco products,
Subcommittee SC 1, Physical and dimensional tests.
This edition cancels and replaces ISO/TR 7821:1982, which has been technically revised.
© ISO 2005 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TS 7821:2005(E)
Introduction
The repeatability and the reproducibility of a particular laboratory method are defined in ISO 3534-1,
ISO 3534-2 and ISO 3534-3. These characteristics may be determined by means of interlaboratory tests as
described in ISO 5725-2.
In addition to the description of the equipment and the test method to be used, often by reference to existing
standards, the organization of such tests also includes the preparation of test materials, i.e. samples that will
serve as media for the studies to be carried out.
It should be noted that, in this type of study, there is rarely any interest in the characteristics of the test
material itself, provided that such characteristics are within the typical range for the materials commonly tested,
and values are determined in this way only in order to obtain the quantitative data necessary for compiling a
statistical report concerning the test method.
Thus, in most cases, every effort is made to obtain lots or samples which are as similar to each other as
possible, in such a way as to reduce the residual variance of the tests and, in the same way, to increase the
accuracy of the conclusions that may be drawn from the global analysis of the results.
Since the individual test samples do not necessarily need to represent the population from which they
are taken, but only have to be identical to each other, the method for their preparation can be quite
different from those needed when the aim of the study is to obtain knowledge of the original
population.
In the case of certain industries, the chemical industry for example, it is relatively easy to make up samples
which are practically identical to each other, as the structure of the material allows it to be divided up so as to
conserve the microscopic or macroscopic homogeneity of the product (e.g. solutions, powders).
In the case of tobacco, however, it is completely different because the raw materials, and even the finished
products, are affected by an intrinsic heterogeneity likely to cause considerable differences between samples
if special precautions are not taken.
Tobacco, as a test medium, can occur in the following forms:
 powder;
 cut tobacco;
 cigarettes;
 leaves or strips.
The method for the preparation of samples of test media depends, in most cases, on the type of test to be
carried out. Nevertheless, it is possible to lay down a few general guidelines applicable to a large number of
collaborative studies, depending on the form in which the material occurs.

iv © ISO 2005 – All rights reserved

---------------------- Page: 4 ----------------------
TECHNICAL SPECIFICATION ISO/TS 7821:2005(E)

Tobacco and tobacco products — Preparation and constitution
of identical samples from the same lot for collaborative studies
for the evaluation of test methods
1 Scope
This Technical Specification provides a practical framework for the operations of dividing a lot (not necessarily
homogeneous) of tobacco or tobacco products into several similar samples intended for collaborative studies,
either within or between laboratories.
2 Preparation of samples
2.1 General
The division of a lot into samples that are similar to each other is very easy if the lot is homogeneous (or can
be made so, according to its physical state), but may be more difficult if it is not. In this case, an appropriate
sampling procedure has to be used in order that the influence of heterogeneity is as small as possible.
It is obviously not possible to describe in detail every case that may arise. The aim of the following examples,
therefore, is to illustrate the principles of, and to give guidance on, the operations to be carried out, which,
moreover, appear simple since
 on the one hand, the given aim is to make up samples that are as similar as possible, and
 on the other hand, to take into account the fact that two units will probably have characteristics which are
most similar if they are sampled from points which are physically close together.
2.2 Powders
2.2.1 Principle
Consider a lot to be divided comprising N g. It is to be divided into n samples of N/n g. Each sample consists of
a number of increments.
Each increment is taken separately from the lot, and should, in theory, be allocated at random to each of the n
samples. In practice, it is sufficient to allocate the increments to each of the n samples in rotation, provided
that the number of cycles of rotation (i.e. number of increments in each sample) is large.
2.2.2 Precautions to be taken
During the preparation of the samples, the following precautions should be taken:
a) work in an atmosphere which has a relative humidity as close as possible to that corresponding to the
equilibrium humidity of the material being handled;
b) work as quickly as possible in order to limit the exchange of moisture between the atm
...

SLOVENSKI STANDARD
SIST-TS ISO/TS 7821:2008
01-julij-2008
1DGRPHãþD
SIST ISO/TR 7821:1995
7REDN3ULSUDYDLGHQWLþQLKY]RUFHYL]LVWHVHULMHGREUDSUDNVD]DSULPHUOMLYH
ãWXGLMHL]UDþXQVNLKPHWRGSUHVNXVRY
Tobacco and tobacco products - Preparation and constitution of identical samples from
the same lot for collaborative studies for the evaluation of test methods
Ta slovenski standard je istoveten z: ISO/TS 7821:2005
ICS:
65.160 7REDNWREDþQLL]GHONLLQ Tobacco, tobacco products
RSUHPD and related equipment
SIST-TS ISO/TS 7821:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

TECHNICAL ISO/TS
SPECIFICATION 7821
First edition
2005-02-15

Tobacco and tobacco products —
Preparation and constitution of identical
samples from the same lot for
collaborative studies for the evaluation of
test methods
Tabac et produits du tabac — Préparation et constitution d'échantillons
identiques à partir d'un même lot pour la conduite d'essais comparatifs
portant sur la qualité des méthodes d'essai




Reference number
ISO/TS 7821:2005(E)
©
ISO 2005

---------------------- Page: 2 ----------------------

ISO/TS 7821:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


©  ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2005 – All rights reserved

---------------------- Page: 3 ----------------------

ISO/TS 7821:2005(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
 an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
 an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TS 7821 was prepared by Technical Committee ISO/TC 126, Tobacco and tobacco products,
Subcommittee SC 1, Physical and dimensional tests.
This edition cancels and replaces ISO/TR 7821:1982, which has been technically revised.
© ISO 2005 – All rights reserved iii

---------------------- Page: 4 ----------------------

ISO/TS 7821:2005(E)
Introduction
The repeatability and the reproducibility of a particular laboratory method are defined in ISO 3534-1,
ISO 3534-2 and ISO 3534-3. These characteristics may be determined by means of interlaboratory tests as
described in ISO 5725-2.
In addition to the description of the equipment and the test method to be used, often by reference to existing
standards, the organization of such tests also includes the preparation of test materials, i.e. samples that will
serve as media for the studies to be carried out.
It should be noted that, in this type of study, there is rarely any interest in the characteristics of the test
material itself, provided that such characteristics are within the typical range for the materials commonly tested,
and values are determined in this way only in order to obtain the quantitative data necessary for compiling a
statistical report concerning the test method.
Thus, in most cases, every effort is made to obtain lots or samples which are as similar to each other as
possible, in such a way as to reduce the residual variance of the tests and, in the same way, to increase the
accuracy of the conclusions that may be drawn from the global analysis of the results.
Since the individual test samples do not necessarily need to represent the population from which they
are taken, but only have to be identical to each other, the method for their preparation can be quite
different from those needed when the aim of the study is to obtain knowledge of the original
population.
In the case of certain industries, the chemical industry for example, it is relatively easy to make up samples
which are practically identical to each other, as the structure of the material allows it to be divided up so as to
conserve the microscopic or macroscopic homogeneity of the product (e.g. solutions, powders).
In the case of tobacco, however, it is completely different because the raw materials, and even the finished
products, are affected by an intrinsic heterogeneity likely to cause considerable differences between samples
if special precautions are not taken.
Tobacco, as a test medium, can occur in the following forms:
 powder;
 cut tobacco;
 cigarettes;
 leaves or strips.
The method for the preparation of samples of test media depends, in most cases, on the type of test to be
carried out. Nevertheless, it is possible to lay down a few general guidelines applicable to a large number of
collaborative studies, depending on the form in which the material occurs.

iv © ISO 2005 – All rights reserved

---------------------- Page: 5 ----------------------

TECHNICAL SPECIFICATION ISO/TS 7821:2005(E)

Tobacco and tobacco products — Preparation and constitution
of identical samples from the same lot for collaborative studies
for the evaluation of test methods
1 Scope
This Technical Specification provides a practical framework for the operations of dividing a lot (not necessarily
homogeneous) of tobacco or tobacco products into several similar samples intended for collaborative studies,
either within or between laboratories.
2 Preparation of samples
2.1 General
The division of a lot into samples that are similar to each other is very easy if the lot is homogeneous (or can
be made so, according to its physical state), but may be more difficult if it is not. In this case, an appropriate
sampling procedure has to be used in order that the influence of heterogeneity is as small as possible.
It is obviously not possible to describe in detail every case that may arise. The aim of the following examples,
therefore, is to illustrate the principles of, and to give guidance on, the operations to be carried out, which,
moreover, appear simple since
 on the one hand, the given aim is to make up samples that are as similar as possible, and
 on the other hand, to take into account the fact that two units will probably have characteristics which are
most similar if they are sampled from points which are physically close together.
2.2 Powders
2.2.1 Principle
Consider a lot to be divided comprising N g. It is to be divided into n samples of N/n g. Each sample consists of
a number of increments.
Each increment is taken separately from the lot, and should, in theory, be allocated at random to each of the n
samples. In practice, it is sufficient to allocate the increments to each of the n samples in rotation, provided
that the number of cyc
...

SPÉCIFICATION ISO/TS
TECHNIQUE 7821
Première édition
2005-02-15


Tabac et produits du tabac — Préparation
et constitution d'échantillons identiques
à partir d'un même lot pour la conduite
d'essais comparatifs portant sur la
qualité des méthodes d'essai
Tobacco and tobacco products — Preparation and constitution of
identical samples from the same lot for collaborative studies for the
evaluation of test methods




Numéro de référence
ISO/TS 7821:2005(F)
©
ISO 2005

---------------------- Page: 1 ----------------------
ISO/TS 7821:2005(F)
PDF – Exonération de responsabilité
Le présent fichier PDF peut contenir des polices de caractères intégrées. Conformément aux conditions de licence d'Adobe, ce fichier
peut être imprimé ou visualisé, mais ne doit pas être modifié à moins que l'ordinateur employé à cet effet ne bénéficie d'une licence
autorisant l'utilisation de ces polices et que celles-ci y soient installées. Lors du téléchargement de ce fichier, les parties concernées
acceptent de fait la responsabilité de ne pas enfreindre les conditions de licence d'Adobe. Le Secrétariat central de l'ISO décline toute
responsabilité en la matière.
Adobe est une marque déposée d'Adobe Systems Incorporated.
Les détails relatifs aux produits logiciels utilisés pour la création du présent fichier PDF sont disponibles dans la rubrique General Info
du fichier; les paramètres de création PDF ont été optimisés pour l'impression. Toutes les mesures ont été prises pour garantir
l'exploitation de ce fichier par les comités membres de l'ISO. Dans le cas peu probable où surviendrait un problème d'utilisation,
veuillez en informer le Secrétariat central à l'adresse donnée ci-dessous.


©  ISO 2005
Droits de reproduction réservés. Sauf prescription différente, aucune partie de cette publication ne peut être reproduite ni utilisée sous
quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit
de l'ISO à l'adresse ci-après ou du comité membre de l'ISO dans le pays du demandeur.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax. + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Publié en Suisse

ii © ISO 2005 – Tous droits réservés

---------------------- Page: 2 ----------------------
ISO/TS 7821:2005(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de 75 % au moins des comités membres
votants.
Dans d'autres circonstances, en particulier lorsqu'il existe une demande urgente du marché, un comité
technique peut décider de publier d'autres types de documents normatifs:
 une Spécification publiquement disponible ISO (ISO/PAS) représente un accord entre les experts dans
un groupe de travail ISO et est acceptée pour publication si elle est approuvée par plus de 50 % des
membres votants du comité dont relève le groupe de travail;
 une Spécification technique ISO (ISO/TS) représente un accord entre les membres d'un comité technique
et est acceptée pour publication si elle est approuvée par 2/3 des membres votants du comité.
Une ISO/PAS ou ISO/TS fait l'objet d'un examen après trois ans afin de décider si elle est confirmée pour trois
nouvelles années, révisée pour devenir une Norme internationale, ou annulée. Lorsqu'une ISO/PAS ou
ISO/TS a été confirmée, elle fait l'objet d'un nouvel examen après trois ans qui décidera soit de sa
transformation en Norme internationale soit de son annulation.
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO/TS 7821 a été élaborée par le comité technique ISO/TC 126, Tabac et produits du tabac, sous-comité
SC 1, Essais physiques et dimensionnels.
Cette édition annule et remplace l'ISO/TR 7821:1982, qui a fait l'objet d'une révision technique.
© ISO 2005 – Tous droits réservés iii

---------------------- Page: 3 ----------------------
ISO/TS 7821:2005(F)
Introduction
La répétabilité et la reproductibilité d'une méthode particulière de laboratoire sont définies dans l'ISO 3534-1,
dans l'ISO 3534-2 et dans l'ISO 3534-3. Ces caractéristiques peuvent être déterminées au moyen d'essais
interlaboratoires de la manière décrite dans l'ISO 5725-2.
En plus de la description de l'équipement et de la méthode d'essai à utiliser, souvent par référence à des
normes existantes, l'organisation de tels essais comporte également la préparation des matériaux d'essai,
c'est-à-dire des échantillons qui serviront de support aux comparaisons à effectuer.
Il convient de noter que, dans ce type d'expérience, on s'intéresse rarement pour elles-mêmes aux
caractéristiques du matériau d'essai, pourvu que ces caractéristiques se situent dans la gamme de celles des
matériaux habituellement soumis aux essais et que leur valeur ne soit ainsi déterminée qu'afin d'obtenir les
éléments quantitatifs nécessaires à l'établissement du compte rendu statistique portant sur la méthode d'essai.
C'est ainsi qu'on s'efforce dans la plupart des cas d'obtenir des lots ou des échantillons aussi semblables que
possible les uns aux autres de manière à réduire la variance résiduelle des essais et à augmenter, par la
même occasion, l'exactitude des conclusions que l'on peut tirer de l'analyse globale des résultats.
Étant donné que les échantillons individuels pour essai ne représentent pas nécessairement la
population dont ils sont tirés mais doivent seulement être identiques les uns aux autres, leur méthode
de préparation peut être tout à fait différente de celle utilisée quand le but de l'étude est d'obtenir une
connaissance de la population d'origine.
Dans le cas de certaines industries, l'industrie chimique par exemple, il est relativement aisé de constituer des
échantillons pratiquement identiques les uns aux autres, la structure du matériau autorisant une division
conservant l'homogénéité microscopique ou macroscopique du produit (par exemple solutions, poudres).
Cependant, il en va tout autrement dans le cas du tabac, la matière première et même les produits finis étant
affectés d'une hétérogénéité intrinsèque qui peut créer des dispersions importantes entre les échantillons si
des précautions spéciales ne sont pas prises.
Le tabac en tant que support d'essai peut se présenter sous les formes suivantes:
 poudre;
 tabac haché (scaferlati);
 cigarettes;
 feuilles ou strips.
La méthode de préparation des échantillons de supports d'essai dépend dans la plupart des cas du type
d'essai à effectuer. Néanmoins il paraît possible de fixer quelques lignes directrices générales applicables,
selon la forme sous laquelle se présente le matériau, à un grand nombre d'essais comparatifs.

iv © ISO 2005 – Tous droits réservés

---------------------- Page: 4 ----------------------
SPÉCIFICATION TECHNIQUE ISO/TS 7821:2005(F)

Tabac et produits du tabac — Préparation et constitution
d'échantillons identiques à partir d'un même lot pour la
conduite d'essais comparatifs portant sur la qualité des
méthodes d'essai
1 Domaine d'application
La présente Spécification technique fournit un cadre pratique aux opérations de division de lot (pas
nécessairement homogène) de tabac ou de produits du tabac en plusieurs échantillons similaires destinés à
des essais comparatifs de laboratoire ou interlaboratoires.
2 Préparation des échantillons
2.1 Généralités
La division d'un lot en échantillons aussi similaires que possible est aisée si le lot est (ou peut selon son état
physique être rendu) homogène, mais elle peut être plus difficile s'il ne l'est pas. Dans ce cas il est nécessaire
de recourir à une méthode d'échantillonnage appropriée afin que l'influence de l'hétérogénéité soit aussi faible
que possible.
Il n'est évidemment pas possible de décrire en détail tous les cas qui peuvent se présenter. Le but des
exemples suivants est donc d'illustrer les principes à appliquer et de donner une ligne directrice pour les
opérations à effectuer qui, par ailleurs, apparaissent comme simples à concevoir lorsqu'on a bien en tête que
 d'une part, l'objectif fixé est de constituer des échantillons aussi identiques que possible,
 d'autre part, il faut tenir compte du fait que, probablement, deux unités ont des caractéristiques d'autant
plus voisines qu'elles sont échantillonnées à partir de points physiquement proches l'un de l'autre.
2.2 Poudre
2.2.1 Principe
Prendre en considération un lot à diviser comportant N grammes. Il s'agit de le diviser en n échantillons de
N/n grammes. Chaque échantillon est constitué d'un certain nombre de prélèvements élémentaires.
Chaque prélèvement élémentaire est tiré séparément du lot, et théoriquement, il convient de l'attribuer au
hasard à l'un des n échantillons. Dans la pratique on se contente d'attribuer les prélèvements élémentaires à
chacun des n échantillons par permutation circulaire, pourvu que le nombre de cycles (c'est-à-dire le nombre
de prélèvements élémentaires affectés à chaque échantillon) soit grand.
© ISO 2005 – Tous droits réservés 1

---------------------- Page: 5 ----------------------
ISO/TS 7821:2005(F)
2.2.2 Précautions à prendre
Lors de la préparation des échantillons, il convient de prendre les précautions suivantes:
a) travailler dans une atmosphère dont le degré hygrométrique est aussi voisin que possible de celui
correspondant à l'humidité d'équilibre du matériau manipulé;
b) travailler aussi vite que possible de façon à limiter les échanges hygroscopiques entre l'atmosphère et le
matériau au cas où la condition a) ne peut être réalisée de façon absolue.
...