Measurement uncertainty arising from sampling (2nd edition, 2019)
- Details
- Published: Saturday, 10 July 2010 22:06
Full title
Measurement 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
From this website:
- Download the English edition (pdf, 1.6 MB) (Last updated: 2019-10-15).
Note: Editorial corrections are available for this edition (below). - Download the German edition (pdf, 4.2 Mb) (Published 2023-11-27)
- Download the Italian edition* (pdf, 1.7 Mb) (Published 2023-05-18)
- Download the Spanish edition (pdf, 2.2 Mb) (Published 2021-05-25)
* Also available from the ISS website.
Additional translations:
- A Czech translation of the 2nd edition is available as Eurachem.CZ guide "KVALIMETRIE 25", available at http://www.eurachem.cz/publikace-detail.php?clanek=19
- A Portuguese translation has been prepared by Relacre and is available from the Relacre website.
Note: In parallel with this Eurachem Guide on sampling uncertainty, Nordtest developed a shorter handbook on sampling, which is available from the Nordtest website.
Editorial corrections
A small number of editorial corrections have been identified since the edition above was approved. These are listed in the sheet of Errata below.
- Errata and corrections to UfS:2019.P2 (pdf 158 kB) (Last updated: 2023-04-27)
Note: The Spanish edition (UfS:2019.P2-ES) published 2021-05-25 includes the corrections listed in the above correction list, up to errata version 1.2.
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
Translation into other languages is permitted for members of Eurachem. Other offers of translation should be directed to the Eurachem Secretariat for permission. The Eurachem policy on maintenance and development of Eurachem guidance, available on the Policies page, gives further information on translation.
Translations of the First edition can be found in the publication archive, here.
The first edition of the EURACHEM Guide for “Quantifying Uncertainty in Analytical Measurement” was published in 1995 based on the ISO "Guide to the Expression of Uncertainty in Measurement". The second edition was prepared in collaboration with CITAC in 2000 in the light of practical experience of uncertainty estimation in chemistry laboratories and the even greater awareness of the need to introduce formal quality assurance procedures by laboratories. The second edition stressed that the procedures introduced by a laboratory to estimate its measurement uncertainty should be integrated with existing quality assurance measures, since these measures frequently provide much of the information required to evaluate the measurement uncertainty.
This document represents the current state-of-the-art with respect to the selection and use of proficiency testing schemes, and the interpretation of results and evaluations given in proficiency testing schemes. Although aimed primarily at staff in analytical laboratories, it is also useful for customers of laboratories, assessors working for accreditation bodies and other external users of PT scheme results.
This Guide gives detailed guidance for the establishment of metrological traceability in quantitative chemical analysis, based on the definition in the international vocabulary of basic and general terms in metrology (VIM). Though it is aimed principally at testing and measurement laboratories carrying out chemical measurement, the principles are expected to apply from routine analysis to basic research. The document is intended to assist laboratories in meeting the requirements on traceability of results given in ISO/IEC 17025.
This guide has been produced by members of the Eurachem Education and Training Working Group and others co-opted to the Project group for this task.