Measurement uncertainty arising from sampling (2nd edition, 2019)

Full title

UfS CoverMeasurement uncertainty arising from sampling: A guide to methods and approaches
Second edition (2019)

Contents

This Guide aims to describe various methods that can be used to estimate the uncertainties arising from the processes of sampling and the physical preparation of samples. It is intended primarily for specialists such as sampling planners and for analytical chemists who need to estimate the uncertainty associated with their measurement results.

The Guide deals with the case where the measurand is defined in term of the value of the analyte concentration in a sampling target, rather than in just the sample delivered to the laboratory. In this case, the sampling process affects the result and its uncertainty, and sampling is necessarily considered as part of the measurement process. This Guide takes a holistic view of the measurement process to include sampling and sample preparation as well as the analytical process.

The Guide begins by explaining the importance of the total uncertainty in a measurement for making reliable interpretation of measurements, and judging their fitness for purpose. It covers the whole measurement process, defining each of the component steps, and describing the effects and errors that cause uncertainty in the final result, with particular attention to sampling issues.

Two main approaches to the estimation of uncertainty from sampling are described. The empirical approach uses repeated sampling and analysis, under various conditions, to quantify the effects caused by factors such as the heterogeneity of the analyte in the sampling target and variations in the application of one or more sampling protocols, to quantify uncertainty (and usually some of its component parts). The modelling approach uses a predefined model that identifies each of the component parts of the uncertainty, making estimates of each component, and sums them in order to make an overall estimate.

For either approach, the Guide follows the principles of the ISO Guide to the Expression of Uncertainty in Measurement, interpreted for analytical measurement in the Eurachem guide "Quantifying Uncertainty in Analytical Measurement" which is available here.

This Second Edition includes a number of additions and changes. These include

  • the expression of uncertainty of measurement as an 'uncertainty factor' (FU) when the frequency distribution describing the sampling uncertainty is log-normal rather than normal, and guidance on the use of an uncertainty factor in an uncertainty budget.
  • the use of an unbalanced design to estimate uncertainty more cost-effectively than can be achieved using the balanced ‘duplicate method’ design;
  • updates to definitions and references to reflect current international documents and literature, including applications of these methods to on-site and in situ measurements, made at both the macro and the micro scale.

Availability

Note: In parallell with the First edition of this Eurachem Guide on sampling uncertainty, Nordtest developed a shorter handbook on sampling, which is available from the Nordtest website.

Citation

This Guide should be cited* as:

M H Ramsey, S L R Ellison and P Rostron (eds.) Eurachem/EUROLAB/ CITAC/Nordtest/AMC Guide: Measurement uncertainty arising from sampling: a guide to methods and approaches. Second Edition, Eurachem (2019). ISBN (978-0-948926-35-8). Available from http://www.eurachem.org

*Subject to journal requirements.

Translations

No translations of this second edition are yet available. Translations of the First edition can be found in the publication archive, here.

Translation into other languages is permitted for members of Eurachem. Other offers of translation should be directed to the Eurachem Secretariat for permission.