ISO/TR 7821:1982 pdf free.Tobacco — Preparation and constitution of identical samples from the same lot (Code of practice, for collaborative studies for evaluating methods of test).
The repeatability and the reproducibility of a particular laboratory method are defined by ISO 3534. These characteristics may be determined by means of inter-laboratory tests as described in ISO 5725.
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 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 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 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 such 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 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 samples which are practically identical to each other, as the structure of the material aHows 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 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.
1 Scope and field of application
This Technical Report 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 References
ISO 3534, Statistics — Vocabulaty and symbols.
ISO 5725, Precision of test methods — Determination of repeatability and reproducibility by inter-laboratory tests.ISO/TR 7821:1982 pdf free download.