• Table of Content
• Foreword
• Scope
• Uncertainty
• Analytical Measurement
• The Process
• Step 1: Specification
• Step 2: Identification
• Step 3: Quantification
• Step 4: Calculation
• Reporting Uncertainty
• Appendix A: Examples
  • Example 1: Calibration Standard
  • Example 2: Standardising NaOH
  • Example 3: An Acid/Base Titration
  • Example 4: In-house Validation Studies
  • Example 5: Determ. Cadmium Release
  • Example 6: Crude Fibre in Animal Feed
  • Example 7: Lead in Water - double IDMS
• Appendix B: Definitions
• Appendix C: Analytical Proc.
• Appendix D: Analyse U Sources
• Appendix E: Statistics
• Appendix F: MU at the Limit
• Appendix G: Common Sources
• Appendix H: Bibliography

1. Scope and Field of Application

1.1. This Guide gives detailed guidance for the evaluation and expression of uncertainty in quantitative chemical analysis, based on the approach taken in the ISO "Guide to the Expression of Uncertainty in Measurement" [h.2]. It is applicable at all levels of accuracy and in all fields - from routine analysis to basic research and to empirical and rational methods (see section 5.3.). Some common areas in which chemical measurements are needed, and in which the principles of this Guide may be applied, are:

• Quality control and quality assurance in manufacturing industries.
• Testing for regulatory compliance.
• Testing utilising an agreed method.
• Calibration of standards and equipment.
• Measurements associated with the development and certification of reference materials.
• Research and development.

1.2. Note that additional guidance will be required in some cases. In particular, reference material value assignment using consensus methods (including multiple measurement methods) is not covered, and the use of uncertainty estimates in compliance statements and the expression and use of uncertainty at low levels may require additional guidance. Uncertainties associated with sampling operations are not explicitly treated.

1.3. Since formal quality assurance measures have to been introduced by laboratories in a number of sectors this second EURACHEM Guide is now able to illustrate how data from the following procedures may be used for the estimation of measurement uncertainty:

• Evaluation of the effect of the identified sources of uncertainty on the analytical result for a single method in a single laboratory.
• Results from defined internal quality control procedures in a single laboratory.
• Results from collaborative trials used to validate methods of analysis in a number of competent laboratories.
• Results from proficiency test schemes used to assess the analytical competency of laboratories.

1.4. It is assumed throughout this Guide that, whether carrying out measurements or assessing the performance of the measurement procedure, effective quality assurance and control measures are in place to ensure that the measurement process is stable and in control. Such measures normally include, for example, appropriately qualified staff, proper maintenance and calibration of equipment and reagents, use of appropriate reference standards, documented measurement procedures and use of appropriate check standards and control charts. Reference [h.6] provides further information on analytical QA procedures.