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EURACHEM CITAC Guide , Traceability in Chemical, Measurement. A guide to achieving comparable, results in chemical measurement. Drafting Editors, S L R Ellison LGC UK , B King UK . M R sslein EMPA Switzerland , M Salit NIST USA , A Williams UK . Composition of the Working Group, EURACHEM Members.
A Williams Chairman UK, S Ellison Secretary LGC Teddington UK. M Berglund Institute for Reference Materials and, Measurements Belgium. W Haesselbarth Bundesanstalt fur Materialforschung und. Prufung Germany, K Hedegaard EUROM II, R Kaarls Netherlands Measurement Institute The. Netherlands, R Kaus EURACHEM Germany, M R sslein EMPA St Gallen Switzerland. A van der Veen Netherlands Measurement Institute The. Netherlands, M Walsh State Laboratory Ireland, W Wegscheider University of Leoben Austria.
H van de Wiel National Institute of Public Health and the. Environment The Netherlands, R Wood Food Standards Agency UK. CITAC Members, B King UK, Acknowledgements M Salit National Institute of Standards and Technology. USA, This document has been produced primarily by a A Squirrell NATA Australia. joint Eurachem CITAC Working Group with the, composition shown right The editors are grateful AOAC Representative. to all these individuals and organisations and to A Pohland AOAC International. others who have contributed comments advice and,assistance EA Representative.
W Richter PTB Germany, Production of this Guide was in part supported under. contract with the UK Department of Trade and,Industry as part of the National Measurement. System Valid Analytical Measurement VAM ,Programme . EURACHEM CITAC Guide Traceability in Chemical Measurement. Preface, Measurement underpins a wide range of socio economic activities both domestic and. international Every day thousands of chemical measurements support decisions on food safety . health and environmental protection The global market too needs accurate and reliable. measurements so that technical barriers to trade can be minimised In all these sectors the. concept of tested once accepted everywhere is increasingly important and the need for reliable. measurement results that can be compared across space and time has never been greater Reliable. measurements depend critically on competent staff validated and tested methods comprehensive. quality systems and traceability to appropriate measurement references Recognition of these. requirements is underscored by the increasing adoption of standards and measurement quality. systems such as laboratory accreditation against ISO 17025 1999 or the pharmaceutical. industry s GLP and cGMP requirements , To achieve comparability of results over space and time it is essential to link all the individual.
measurement results to some common stable reference or measurement standard Results can be. compared through their relationship to that reference This strategy of linking results to a. reference is termed traceability , The International Vocabulary of Basic and General terms in Metrology VIM 1 defines. traceability as the , property of the result of a measurement or the value of a standard whereby it can be. related to stated references usually national or international standards through an. unbroken chain of comparisons all having stated uncertainties . This definition implies a need for effort at national and international level to provide widely. accepted reference standards and at the individual laboratory level to demonstrate the necessary. links to those standards , At the national and international level comparability between national measurement systems is. being continually improved by intercomparison of measurement standards at the National. Metrology Institute NMI level A multilateral mutual recognition arrangement was signed in. 1999 by the member nations of the Meter Convention in response to the need for an open . transparent and comprehensive scheme to give users reliable quantitative information on the. comparability of national metrology systems , Individual measurement and testing laboratories play their part by careful use of appropriate. measurement and reference standards for calibration and control of their measurement processes . In an increasingly regulated environment however laboratories are under greater pressure to. demonstrate that their use of measurement and reference standards is indeed both appropriate and. sufficient , This is particularly true in analytical chemistry Many of the physical quantities used in routine.
chemical measurement are underpinned by extensive and effective calibration and traceability. systems making the establishment of traceability for these quantities relatively straightforward . However the values of chemical quantities involved are typically drawn from a wide range of. reference materials and data with varying pedigree and provenance requiring especial care and. judgement in selection of references Chemical measurements also typically require confirmation. i, of identity as well as measurement of amount Another challenge is the measurement of a species. in complex matrices which may influence the apparent value of the measured species Further it. is not uncommon for useful chemical results to arise from the measurement of operationally. defined species for example extractable cadmium sometimes called empirical . measurements In such circumstances it is not always so straightforward to identify the. requirements for traceability or to demonstrate that the traceability in place is adequate . The purpose of the present document is accordingly to provide guidance on identifying. traceability requirements and establishing traceability of measurement and test results The. document describes a consistent set of principles which laboratories can apply in order to. establish traceability for their measurement results and pays particular attention to the use of. appropriate references for chemical quantities , 1 International vocabulary of basic and general terms in metrology ISO Geneva 1993 . ii, Traceability in Chemical Measurement Contents. Contents, EURACHEM CITAC Guide Traceability in Chemical Measurement i. Preface i,Contents 1,1 Scope and Field of Application 3.
2 Introduction 3,3 Principles of traceability 6,3 1 Methods Measurands and Results 6. 3 2 Measurement scales standards and units 6,3 3 Calibration 7. 3 4 Effects on measurement results 7,3 5 Controlling fixed conditions 8. 3 6 Controlling variables with calibration standards 9. 3 7 Common references allow arbitrary definition 11. 3 8 Role of method development 11,3 9 Role of method validation 11. 3 10 Traceability and measurement uncertainty 12,4 Traceability The International Definition 13.
5 International System of Quantities and Units SI 13. 6 Establishing Traceability 15, 6 1 Essential activities in establishing traceability 15. 6 2 Specifying the measurand and required uncertainty 15. 6 3 Choosing a suitable method 16,6 4 Validation 16. 6 5 Importance of different influence quantities 18. 6 6 Choosing and applying appropriate reference standards 18. 6 7 Uncertainty estimation 19,7 Choice of the Reference 20. 7 1 Introduction 20,ECTRACE 2003 Page 1, Traceability in Chemical Measurement Contents. 7 2 Physical measurements 20,7 3 Confirmation of identity 21.
7 4 Calibration with certified reference materials 21. 7 5 Calibration with other materials 22,7 6 Calibration using reference data 23. 7 7 Reference materials for Method Development Validation and Verification 23. 7 8 Assessing the traceability of commercial reference materials 24. 8 Reporting Traceability 24,9 Conclusion 25,10 Bibliography 26. Appendix Examples of Establishing Traceability 27,1 Preparation of a calibration standard 28. 2 Cadmium Release from Ceramic Ware 32,ECTRACE 2003 Page 2. Traceability in Chemical Measurement Scope and Field of Application. 1 Scope and Field of Application, 1 1 This Guide gives detailed guidance for the establishment of measurement traceability in.
quantitative chemical analysis based on the definition in the International Vocabulary Of Basic. And General Terms in Metrology VIM 1 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 also intended to assist laboratories. in meeting the requirements on traceability of results given in ISO 17025 . 1 2 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 . Measurement and Testing for regulatory compliance . Measurement and Testing utilising an agreed method. Calibration of standards and equipment , Measurements associated with the development and certification of reference materials . Research and development , 1 3 Though this guide discusses measurement uncertainty and method validation in relation to. their role in traceability a detailed description is not attempted in either case Readers are. referred to the Bibliography for additional guidance . 1 4 Traceability is necessary but not sufficient for reliable results other measures are necessary . It is accordingly 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 of. equipment and reagents use of documented measurement procedures and control charts . Reference 2 provides further information on analytical QA procedures . 2 Introduction, 2 1 Good analytical results are essential so that reliable decisions can be made A key property of. good results is comparability the ability to compare results meaningfully wherever they. originate Comparability is provided by among other things traceability to a consistent and. agreed set of measurement units and scales For most chemical measurement results this is best. provided by the SI the internationally accepted system of units While it is recognised that other. units may be required this guide will generally assume that measurements will be expressed in . or rely on SI units , 2 2 Traceability is not a new concept in chemical analysis Before the advent of automation and.
instrumental techniques titrimetry and gravimetry were the workhorses of the chemistry. laboratory and even though the average analyst may not explicitly refer to or recognise the. significance of uncertainty or traceability the core elements for their attainment were in place . For example great care was and is paid to the preparation and calibration of volumetric. solutions including their linkage to SI With more complex measurement methods it is not. ECTRACE 2003 Page 3, Traceability in Chemical Measurement Introduction. always so straightforward to identify the requirements for traceability or to demonstrate that the. traceability in place is adequate The purpose of the present document is accordingly to provide. guidance on identifying traceability requirements and establishing adequate traceability . 2 3 There has been much discussion both at workshops and in the literature about the role of. traceability in chemical measurement This document is based on the following principles which. are fully in line with the VIM definition of traceability . Method development establishes a procedure for obtaining an acceptable estimate of the. measurand This procedure includes an equation that describes how to calculate a measurement. result from other measured quantities and specifies the conditions under which this equation is. expected to hold , Validation demonstrates that this equation and set of conditions is sufficiently complete for. the purpose in hand , Establishing traceability ensures that the values of these measured quantities and the values of the. specified conditions are related to appropriate standards This is achieved by calibration using. appropriate measurement standards Calibration is essential for the critical values in the. measurement for less critical values the required control may be less rigorous . These basic principles are summarised in Box 1 They are discussed in detail in section 3 and. related to the internationally accepted definition of traceability in section 4 . 2 4 The document identifies the key elements in Box 1 Summary of basic principles. establishing traceability as, 1 We assume that an acceptable estimate y of the. i Specifying the measurand scope of measurand value can be obtained from. measurements and the required, uncertainty y f x1 x 2 x m xm 1 xm 2 xn.
ii Choosing a suitable method of that is y is calculated from x1 xm using a. estimating the value that is a relationship f which is valid under measurement. measurement procedure with associated conditions specified by xm 1 xn . calculation an equation and 2 Validation checks that the equation above is. measurement conditions sufficient using suitable tests . iii Demonstrating through validation that 3 y is then considered traceable to x1 xn. EURACHEM CITAC Guide Traceability in Chemical Measurement Preface Measurement underpins a wide range of socio economic activities both domestic and international Every day thousands of chemical measurements support decisions on food safety health and environmental protection The global market too needs accurate and reliable

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