Uncertainty from sampling, in the context of fitness for purpose

Sampling is an integral part of nearly all chemical measurement and often makes a substantial or even a dominant contribution to the uncertainty of the measurement result. In contrast with analysis, however, the uncertainty contribution from sampling has usually been ignored. Indeed, far less is known about sampling uncertainty, although in some application sectors it is known to exceed the analytical uncertainty, especially when raw materials (natural or industrial) are under test. In 1995 the authors of this paper proposed a framework of concepts and procedures for studying, quantifying, and controlling the uncertainty arising from the sampling that normally precedes analysis. Many of the ideas were based on analogy with well-established procedures and considerations relating to quality of analytical measurement, ideas such as validation of the sampling protocol, sampling quality control and fitness for purpose. Since that time many of these ideas have been explored experimentally and found to be effective. This paper is a summary of progress to date.