Guides

Guides

Current Eurachem Guides

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.

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.

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.

Quantifying Uncertainty in Analytical Measurement, 3rd Edition (2012)

Contents

This guide has been produced by a joint EURACHEM/CITAC Measurement Uncertainty Working Group.

Cause and Effect diagramThe 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 third edition retains the features of the second edition and adds information based on developments in uncertainty estimation and use since 2000. The additional material provides:

  • Improved guidance on the expression of uncertainty near zero; Monte Carlo uncertainty evaluation
  • New guidance on the use of Monte Carlo methods for uncertainty evaluation;
  • Improved guidance on the use of proficiency testing data:
  • Improved guidance on the assessment of compliance of results with measurement uncertainty.

The guide therefore provides explicitly for the use of validation and related data in the construction of uncertainty estimates in full compliance with the formal ISO Guide principles set out in the ISO Guide to the Expression of Uncertainty in measurement. The approach is also consistent with the requirements of ISO/IEC 17025:2005.

Availability

You may download the guide from this website at no cost (pdf, 1.908 MB).

NB: See also "Comments and errata" below.

Citation

This guidance should be cited* as
"S L R Ellison and A Williams (Eds). Eurachem/CITAC guide: Quantifying Uncertainty in Analytical Measurement, Third edition, (2012) ISBN 978-0-948926-30-3. Available from www.eurachem.org."

*Subject to journal requirements.

Translations

The current (third) edition of this guide is currently available in for download in English, Spanish* and Farsi*.

A French translation is also available from the French National Measurement Institute, LNE; you can obtain the French translation from the LNE website.

The 3rd edition is also commercially available in Japanese from the publisher Maruzen Publishing: see http://pub.maruzen.co.jp/book_magazine/news_event/2013/bunsekihutashika.html or  Amazon Japan.

The 2nd edition (2000) has been translated into Italian, Portuguese, Russian and Swedish. The 1st edition (1995) has been translated into Czech, Lithuanian, Russian and Spanish. The Italian translation of the 2nd edition can be downloaded from the INRIM website (http://www.inrim.it/biblio/eurachem/index_i.shtml). For details about the translation of the 2nd edition of the Guide into Russian please contact This email address is being protected from spambots. You need JavaScript enabled to view it. from the D. I. Mendeleyev Institute for Metrology. For details about the other translations please contact the Eurachem representative in the respective country or the Eurachem Secretariat.

Comments and errata

Since publication of the third edition of the Guide in 2012, a number of minor typographical issues have been identified. Although not sufficient to justify revision and re-issue of the complete Guide and translations, some affect the detailed results of calculations in examples, making it hard to check results exactly. The Measurement Uncertainty and Traceability WG have accordingly prepared a list of comments and corrections for reader information. These are likely to be implemented in future editions.

Acknowledgements

Production of the English editions of the guide was supported by the UK National Measurement System.

The Spanish translation of the 3rd edition was provided by P Morillas (Spain) and the Farsi translation by Mohammad Rahmani (Iran).

Contact point

Any comment or query about the content of this guide should be directed to the Working Group Secretary.

 

Figures

1. Cause and Effect diagram: Uncertainty sources in leachable cadmium measurement

2. A histogram of 500 Monte Carlo simulations. See Appendix E.3 in the Guide for details

Selection, Use and Interpretation of Proficiency Testing (PT) Schemes by Laboratories (2011)

Contents

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 this is 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.

The main topics covered by the Guide are:

a) the aims and benefits of participation in PT schemes;
b) selecting the most appropriate PT scheme;
c) understanding the basic statistics and performance scoring used by the PT providers;
d) using and interpreting the PT results in order to improve the overall performance of the laboratory.

ptguide2011_132

This second edition, approved in 2011, has been prepared by the EEE-PT Working Group (EA-Eurolab-Eurachem). EQALM (European Organisation for External Quality Assurance Programmes in Laboratory Medicine) as an affiliate member was also involved in this revision.

Availability

You may download the document from this website (pdf, 460 kB).

Translations

This guide is currently available in English and in Farsi.

Translation into other languages is permitted for members of Eurachem.

Accreditation for Microbiological Laboratories (2013)

Contents

80px-Anthrax cultureThis document has been produced primarily by an ad hoc Eurachem Working Group in collaboration with the EA (European co-operation for Accreditation) Laboratory Committee. It provides microbiological laboratories with appropriate information and guidance on how to fulfil the requirements of ISO/IEC 17025.

Note: The previous version of this guide was additionally approved as EA Guide EA 4/10 G:2002. For further information on the status of EA 4/10 G:2002 see the archive page of the 2002 Guide and the EA website.

Amendment (May 2014): The title page of the present website version (.P2) has been amended from the 2013 printing to remove an incorrect reference to EA 4/10.

Availability

You may download the guide from this website at no cost (pdf, 272 kB).

Translations

Translation into other languages is permitted for members of Eurachem.