1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58constitution of identical samples from the same lot for collaborative studies for the evaluation of
2、 test methodsICS 65.160Tobacco and tobacco products Preparation and DRAFT FOR DEVELOPMENTDD ISO/TS 7821:2005DD ISO/TS 7821:2005This Draft for Development was published under the authority of the Standards Policy and Strategy Committee and comes into effect on 18 November 2005 BSI 18 November 2005ISB
3、N 0 580 47324 4another 3 years or to withdraw it. Comments should be sent in writing to the Secretary of BSI Technical Committee AW/40, Tobacco and tobacco products, at 389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possible, an appropriat
4、e revision of the text.A list of organizations represented on this committee can be obtained on request to its secretary.Cross-referencesThe British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “Interna
5、tional Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.Summary of pagesThis document comprises a front cover, an inside front cover, the ISO/TS title page, pages ii to iv, pages 1 to 5 and a back cover.The BSI copyrigh
6、t notice displayed in this document indicates when the document was last issued.Amendments issued since publicationAmd. No. Date Commentsthat UK experience can be reported to the international organization responsible for the Technical Specification. A review of this publication will be initiated no
7、t later than 3 years after its publication by the international organization so that a decision can be taken on its status at the end of its 3-year life. Notification of the start of the review period will be made in an announcement in the appropriate issue of Update Standards.According to the repli
8、es received by the end of the review period, the responsible BSI Committee will decide whether to support the conversion into an international standard, to extend the life of the Technical Specification for National forewordThis Draft for Development reproduces verbatim ISO/TS 7821:2005. It supersed
9、es BS 6245-2:1983 which is withdrawn.This publication is not to be regarded as a British Standard.It is being issued in the Draft for Development series of publications and is of a provisional nature because the methods given in this document are still being assessed. It should be applied on this pr
10、ovisional basis, so that information and experience of its practical application may be obtained.Comments arising from the use of this Draft for Development are requested so Reference numberISO/TS 7821:2005(E)TECHNICAL SPECIFICATION ISO/TS7821First edition2005-02-15Tobacco and tobacco products Prepa
11、ration and constitution of identical samples from the same lot for collaborative studies for the evaluation of test methods Tabac et produits du tabac Prparation et constitution dchantillons identiques partir dun mme lot pour la conduite dessais comparatifs portant sur la qualit des mthodes dessai D
12、D ISO/TS 7821:2005ii iiiForeword 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
13、 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 Commiss
14、ion (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
15、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 de
16、cide 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
17、 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
18、 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
19、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 d
20、imensional tests. This edition cancels and replaces ISO/TR 7821:1982, which has been technically revised. DD ISO/TS 7821:2005iv 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
21、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 se
22、rve 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 determine
23、d 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
24、 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 me
25、thod 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 othe
26、r, 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
27、 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,
28、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. DD ISO/TS 7821:20051Tobacco and tobacco products Preparation and constitu
29、tion 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
30、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
31、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
32、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 m
33、ost 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
34、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
35、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 moi
36、sture between the atmosphere and the material if it is not possible to satisfy completely condition a). DD ISO/TS 7821:20052 2.2.3 Example A gross sample of 1 kg of powder is to be divided into 10 samples of 100 g. The condition to be fulfilled for the collaborative studies is not that 10 samples of
37、 exactly 100 g each should be obtained, but that each sample of approximately 100 g should be similar, from the physical and chemical point of view, to each of the others. a) Manual method After mixing the gross sample as thoroughly as possible, place the pile on a tray or in a receptacle from which
38、 the material can be easily scooped out. Use a spoon, ladle or measure, of capacity between 5 g and 10 g for example. Provide 10 boxes capable of holding at least 100 g each. Taking a succession of increments, using the spoon, ladle or measure, feed, in turn, box 1, box 2, , box 10. Each sample is t
39、hus made up of at least 10 (10 to 20) increments. When the initial pile is almost exhausted, i.e. when there is only enough left for one round of 10 increments, it is recommended that distribution be finished with a measure of smaller capacity. This method guarantees that the 10 samples thus constit
40、uted are as similar as possible. Any mixing of the gross sample will cause variation of particle size and density through the pile from top to bottom, and this should be taken into account when taking increments. b) Automatic method Use a mechanical device such that, at each revolution, the quantity
41、 attributed to each sample is less than or equal to one-tenth of the total mass of the final sample. 2.3 Cut tobacco 2.3.1 Principle Exactly the same principle as for powders is applicable. In practice, handling is more difficult as the tobacco can form tangles, especially if it is in long strands.
42、The temptation to make up the increments from wads or lumps should be resisted and, instead, they should be broken down so that they can be divided between all the samples. As a general rule, each sample should be made up of at least 10 increments (and more if possible). In addition, increments shou
43、ld always be distributed to each sample in a standard rotation. The increment should be adapted to the size of the lot and the number of samples to be obtained. 2.3.2 Special precautions Cut tobacco always tends to settle, i.e. handling causes a certain amount of separation of the short strands whic
44、h collect at the bottom of the receptacle. In order to avoid causing an artificial heterogeneity between samples when the long strands have been exhausted, it is important to distribute the short strands equally between samples using an instrument such as a scoop or spoon, which prevents the loss of
45、 these strands at the time of distribution. DD ISO/TS 7821:200532.4 Cigarettes 2.4.1 Cigarettes to be sampled from the production machine It is known that there are serial correlations between the characteristics of cigarettes, i.e. on average, the probability of cigarettes being identical is greate
46、r the shorter the interval between their fabrication by the cigarette-making machine. For example, if 10 samples, each of 100 cigarettes, are to be prepared, proceed as follows: a) take a series of 10 consecutive cigarettes and distribute them between the 10 samples to be made up; b) repeat the oper
47、ation 100 times. NOTE There is no disadvantage if there is a gap between taking increments (of 10 cigarettes), i.e. if the tenth cigarette of one increment and the first cigarette of the next increment are not successive cigarettes. To save time, it is permissible to take increments successively. Fo
48、r example, 20, 50 or even 100 successive cigarettes may be taken. In this case, it is undesirable to keep the cigarettes in bulk, and they should be kept in individual increments, labelled in the order of manufacture, and should be distributed in that order, rotating round the 10 samples to be const
49、ituted in the usual manner. For this purpose, automatic sampling devices may be used. Experience shows that making up samples in this way gives results as good as, or even better than, selection by mass or draw resistance as far as comparability of samples is concerned. 2.4.2 Cigarettes sampled from a bulk cigarette storage before packing For the same reasons as described in 2.4.1, it is important to avoid constituting the samples by taking each of them in a group from the case. Instead, it is recommended that the foll
