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1、BRITISH STANDARD BS 6245-2: 1983 Sampling tobacco and tobacco products Part 2: Method of preparing samples for collaborative studies UDC 633.71:663.97:620.113 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 This British Standa
2、rd, having been prepared under the direction of the Food and Agriculture Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 October 1983 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference FAC/11 Draft
3、for comment 83/51098 DC ISBN 0 580 13477 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Food and Agriculture Standards Committee (FAC/-) to Technical Committee FAC/11 upon which the following bodies were represented: Department of Ind
4、ustry (Laboratory of the Government Chemist) Tobacco Advisory Council Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 BSI 10-1999i Contents Page Committees resp
5、onsibleInside front cover Forewordii 0Introduction1 1Scope and field of application1 2References1 3Preparation of samples1 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 ii BSI 10-199
6、9 Foreword This Part of BS 6245 has been prepared under the direction of the Food and Agriculture Standards Committee and is technically equivalent to ISO/TR 7821:1982 Tobacco Preparation and constitution of identical samples from the same lot (Code of practice, for collaborative studies for evaluat
7、ing methods of test) published by the International Organization for Standardization (ISO). It will be of value to all those concerned with the evaluation of methods of test. For ease of reproduction the text of the International Technical Report has been used for this British Standard. Some termino
8、logy and certain conventions are not identical with those used in British Standards. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of its
9、elf confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be i
10、ndicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 BSI 10-19991 0 Introduction The repeatability and the reproducibility of a particular laboratory method are defined by
11、BS 5532. These characteristics may be determined by means of inter-laboratory tests as described in BS 5497-1. In addition to the description of the equipment and the methods of test to be used, often by reference to existing standards, the organization of such tests also includes the preparation of
12、 test materials, i.e. samples which 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 material
13、s 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 method of test. Thus, in most cases, every effort is made to obtain lots or samples which are as similar to each other as possible, in su
14、ch a way as to reduce the residual variance of the tests and, in the same way, to increase the accuracy of the conclusions which 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
15、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 a knowledge of the original population. In the case of certain industries, the chemical industry for example, it is relatively easy to make up sam
16、ples 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, for example solutions, powders, etc. In the case of tobacco, however, it is completely different, because the r
17、aw 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, may occur in the following forms: powder; cut tobacco (scaferlati); cigarettes; leaves or
18、 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 seems possible to lay down a few general guidelines applicable to a large number of collaborative studies, depending on the form in which the material occu
19、rs. 1 Scope and field of application This British Standard 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 Referen
20、ces The titles of the publications referred to in this standard are listed on the inside back cover. 3 Preparation of samples 3.1 General The division of a lot into samples which are similar to each other is very easy if the lot is (or can be made, according to its physical state) homogeneous, but m
21、ay 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 which may arise. The aim of the following examples, therefore, is to i
22、llustrate the principles of, and to give guidance on, the operations to be carried out, which, moreover, appear simple to conceive bearing in mind on the one hand, the given aim, which is to make up samples which are as similar as possible; on the other hand, to take into account the fact that two u
23、nits will probably have characteristics which are most similar if they are sampled from points which are physically close together. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 2 BSI 10-1999 3.2 Powder The initial lot compr
24、ises N g. It has to be divided up into n samples of. 3.2.1 Principle 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 ea
25、ch of the n samples in rotation, provided that the number of cycles of rotation (i.e. number of increments in each sample) is large. 3.2.2 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
26、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 atmosphere and the material if it is not possible to satisfy completely condition a). 3.2.3 Example A gross samp
27、le 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 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
28、 each of the others. 3.2.3.1 Manual method After mixing the gross sample as thoroughly as possible, place the pile on a tray or in a receptacle from which the material can be easily scooped out. Use a spoon, ladle or measure, of capacity between 5 and 10 g for example. Provide 10 boxes capable of ho
29、lding 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 thus 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
30、 increments, it is recommended that distribution be finished with a measure of smaller capacity. This method guarantees that the 10 samples thus constituted 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 botto
31、m, and this should be taken into account when taking increments. 3.2.3.2 Automatic method Use a mechanical device such that, at each revolution, the quantity attributed to each sample is less than or equal to one-tenth of the total mass of the final sample. 3.3 Cut tobacco (scaferlati) 3.3.1 General
32、 Exactly the same principle as for powder is applicable. In practice, handling is more difficult as the tobacco may form tangles, especially if it is in long strands. The temptation to make up the increments from wads or lumps should be resisted, and, instead, they should be broken down so that they
33、 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 should always be distributed to each sample in a standard rotation. Depending on the size of the lot, the increment may be of the order
34、of a large handful, a handful or a pinch. 3.3.2 Special precautions Cut tobacco (scaferlati) always tends to settle, i.e. handling causes a certain amount of separation of the short strands which collect at the bottom of the receptacle. In order to avoid causing an artificial heterogeneity between s
35、amples when the long strands have been exhausted, it is necessary to distribute the short strands equally between samples using an instrument such as a scoop, spoon, etc., which prevents the loss of these strands at the time of distribution. 3.4 Cigarettes 3.4.1 Cigarettes to be sampled from the pro
36、duction 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 greater the shorter the interval between their fabrication by the cigarette making machine. N n - - g Licensed Copy: sheffieldu
37、n sheffieldun, na, Wed Dec 06 12:56:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6245-2:1983 BSI 10-19993 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 to the 10 samples to be made up;
38、 b) repeat the operation 100 times. NOTE 1There 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. NOTE 2To save time, it is permissible to take i
39、ncrements successively. For example 20, 50, or even 100 successive cigarettes can 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
40、the ten samples to be constituted in the usual manner. For this purpose, automatic sampling devices can 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. 3.
41、4.2 Cigarettes sampled from a bulk cigarette storage before packing For the same reasons as described in 3.4.1, it is necessary to avoid constituting the samples by taking each of them in a group from the case. Instead, it is recommended that one of the two following procedures be used in order to c
42、onstitute, for example, 10 samples of 100 cigarettes: a) take successive cigarettes for each sample at random, for example using a table of random numbers to which, for example, the (approximate) coordinates are made to correspond to a point from where each cigarette is taken; b) take each horizonta
43、l row of the storage bin or case as a primary sample and take from it one increment for each of the samples being made up. It is not necessary in this case for the whole row to be allocated; the main point is that each sample should contain cigarettes from every row selected as a primary sample. Pro
44、cedure a) is theoretically the most satisfactory, but it can be unwieldy to apply when there is a large number of samples (greater than 3 or 4), comprising a large number of cigarettes, to be constituted. In current practice, procedure b), which is more rapid, is amply sufficient, because of the par
45、tial stratification which is involved, and thus compensates for the fact that the sampling is not totally at random. 3.4.3 Cigarettes in packets Initial lots of cigarettes in packets may, as appropriate, be made up of: packets in bulk; cartons or units (for example units of 200); boxes. The procedur
46、e to be used for sampling the lot for the purposes laid down in this Technical Report relies on observation of the following principles: a) Take into account the fact that two cigarettes are, probably, most similar in their characteristics, if they originate from the same package unit. b) Adapt the
47、method of sampling to the volume of the samples to be made up. Thus, in certain cases, the packet itself may be considered as an increment, whereas, in other cases, the packets themselves must be opened. 3.4.3.1 Example 1 The initial lot is made up of two boxes each containing 25 units of 10 packets
48、 of 20 cigarettes (boxes of 20 10 25 = 5 000 cigarette units, i.e. 250 packets, or a total of 10 000 cigarettes, 500 packets, 50 cartons). If it is wished to make up, for example, 5 samples (as similar to each other as possible) of 20 packets from the initial lot of 500 packets, constitution of the
49、samples by systematically sampling 2 units of 10 packets to make up each sample will obviously be avoided, since internally homogeneous samples would be obtained, but there would be greater differences between them than within them. The best procedure would be the following: From each box, take at random 1 unit in 5. Thus 10 units (2 5) each of 10 packets will be obtained. Each unit can be divided into 5 increments each of two packets, and each sample will then receive one increment from each unit. In this case, the 5 samples of 2 10 packets will b