Metrology in sampling - a first foray (biological materials)

Measurement is the process of determining a correct value of a measurand; definition of the measurand is decisive for an expedient choice of a measurement method. The result of a measurement refers in principle only to the amount of substance actually contributing to the analytical signal. An appropriate definition of the measurand, however, must include a specification of the entire system, for which the result of the measurement is required to apply, i.e., which it is supposed to represent. The concept of representativity therefore assumes importance for the metrological quality of a measurement, and the process with which to ascertain representativity is proper sampling. All systems from which a sample is to be selected are inherently heterogeneous (this is only a matter of the scale of observation), and it is therefore necessary to take into account a contribution from this characteristic, when expressing the uncertainty of the reported value of the measurand. Examples are presented, where methods from metrology are combined with the Theory of Sampling to evaluate the influence of sampling on the uncertainty of results obtained by the analysis of biological materials. (C) 2004 Elsevier B.V. All rights reserved.