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  • 145

    Pure Appl. Chem., Vol. 78, No. 1, pp. 145–196, 2006. doi:10.1351/pac200678010145 © 2006 IUPAC

    INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY

    ANALYTICAL CHEMISTRY DIVISION*

    INTERDIVISIONAL WORKING PARTY FOR HARMONIZATION OF QUALITY ASSURANCE SCHEMES

    THE INTERNATIONAL HARMONIZED PROTOCOL FOR THE PROFICIENCY TESTING OF ANALYTICAL

    CHEMISTRY LABORATORIES

    (IUPAC Technical Report)

    Prepared for publication by MICHAEL THOMPSON1, STEPHEN L. R. ELLISON2,‡, AND ROGER WOOD3

    1School of Biological and Chemical Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK; 2LGC Limited, Queens Road, Teddington Middlesex,

    TW11 0LY, UK; 3Food Standards Agency, c/o Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK

    *Membership of the Analytical Chemistry Division during the final preparation of this report was as follows:

    President: K. J. Powell (New Zealand); Titular Members: D. Moore (USA); R. Lobinski (France); R. M. Smith (UK); M. Bonardi (Italy); A. Fajgelj (Slovenia); B. Hibbert (Australia); J.-Å. Jönsson (Sweden); K. Matsumoto (Japan); E. A. G. Zagatto (Brazil); Associate Members: Z. Chai (China); H. Gamsjäger (Austria); D. W. Kutner (Poland); K. Murray (USA); Y. Umezawa (Japan); Y. Vlasov (Russia); National Representatives: J. Arunachalam (India); C. Balarew (Bulgaria); D. A. Batistoni (Argentina); K. Danzer (Germany); E. Domínguez (Spain); W. Lund (Norway); Z. Mester (Canada); Provisional Member: N. Torto (Botswana).

    ‡Corresponding author: E-mail: s.ellison@lgc.co.uk

    Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.

  • The International Harmonized Protocol for the proficiency testing of analytical chemistry laboratories

    (IUPAC Technical Report)

    Abstract: The international standardizing organizations—AOAC International, ISO, and IUPAC—cooperated to produce the International Harmonized Protocol for the Proficiency Testing of (Chemical) Analytical Laboratories. The Working Group that produced the protocol agreed to revise that Protocol in the light of re- cent developments and the experience gained since it was first published. This re- vision has been prepared and agreed upon in the light of comments received fol- lowing open consultation.

    Keywords: harmonized; IUPAC Analytical Chemistry Division; uncertainty; analysis; proficiency testing; protocol.

    CONTENTS

    PART 1: FOREWORD AND INTRODUCTION 148 1.0 Foreword 148 1.1 Rationale for proficiency testing 149 1.2 Proficiency testing in relation to other quality-assurance methods 149

    PART 2: THE HARMONIZED PROTOCOL; ORGANIZATION OF PROFICIENCY 150 TESTING SCHEMES 2.1 Scope and field of application 150 2.2 Terminology 150 2.3 Framework of proficiency testing 151 2.4 Organization 151 2.5 Duties of the advisory committee 152 2.6 Review of the scheme 152 2.7 Test materials 152 2.8 Frequency of distribution 153 2.9 Assigned value 153 2.10 Choice of analytical method by participant 154 2.11 Assessment of performance 154 2.12 Performance criteria 154 2.13 Reporting of results by participants 154 2.14 Reports provided by scheme provider 154 2.15 Liaison with participants 155 2.16 Collusion and falsification of results 155 2.17 Repeatability 156 2.18 Confidentiality 156

    M. THOMPSON et al.

    © 2006 IUPAC, Pure and Applied Chemistry 78, 145–196

    146

  • PART 3: PRACTICAL IMPLEMENTATION 156 3.1 Conversion of participants’ results into scores 156 3.2 Methods of determining the assigned value 158 3.3 Estimating the assigned value as the consensus of participants’ results 160 3.4 Uncertainty on the assigned value 162 3.5 Determination of the standard deviation for proficiency assessment 163 3.6 Participant data reported with uncertainty 165 3.7 Scoring results near the detection limit 167 3.8 Caution in the uses of z-scores 168 3.9 Classification, ranking, and other assessments of proficiency data 168 3.10 Frequency of rounds 169 3.11 Testing for sufficient homogeneity and stability 169

    COLLECTED RECOMMENDATIONS 174 REFERENCES 175 APPENDIX 1: RECOMMENDED PROCEDURE FOR TESTING A MATERIAL FOR 177

    SUFFICIENT HOMOGENEITY APPENDIX 2: EXAMPLE OF CONDUCTING A TEST FOR STABILITY 181 APPENDIX 3: EXAMPLES OF PRACTICE IN DETERMINING A PARTICIPANT 182

    CONSENSUS FOR USE AS AN ASSIGNED VALUE APPENDIX 4: ASSESSING Z-SCORES IN THE LONGER TERM: SUMMARY SCORES 185

    AND GRAPHICAL METHODS APPENDIX 5: METHOD VALIDATION THROUGH THE RESULTS OF PROFICIENCY 188

    TESTING SCHEMES APPENDIX 6: HOW PARTICIPANTS SHOULD RESPOND TO THE RESULTS OF 189

    PROFICIENCY TESTS APPENDIX 7: GUIDE TO PROFICIENCY TESTING FOR END-USERS OF DATA 194

    © 2006 IUPAC, Pure and Applied Chemistry 78, 145–196

    Harmonized Protocol for proficiency testing 147

  • PART 1: FOREWORD AND INTRODUCTION

    1.0 Foreword

    In the 10 years since the first version of this protocol was published [1], proficiency testing has bur- geoned. The method has become widely used in many sectors of chemical analysis, and many new pro- ficiency testing schemes have been launched worldwide [2]. A detailed study of proficiency testing for the analytical chemistry laboratory has been undertaken [3]. The International Organization for Standardization (ISO) has published a guide to proficiency testing [4] and a standard on statistical meth- ods for use in proficiency testing [5]. The International Laboratory Accreditation Corporation (ILAC) has published a document on the quality requirements for proficiency testing [6], and many proficiency testing schemes have now been accredited. In addition, the clarification over the last decade of the ap- plication of the uncertainty concept to chemical measurement has had an effect on the way in which we view proficiency testing. This extraordinary development of proficiency testing is both a recognition of its unrivalled power to expose unexpected problems in analysis and the current requirement of partici- pation in a proficiency testing scheme as part of the accreditation of analytical laboratories.

    As a result of all this activity in many different analytical sectors, together with the considerable amount of research that has been conducted, the analytical community has built up a large body of new experience with proficiency testing. It is pleasing to note that no substantive modifications of the fun- damental ideas and principles of the 1993 Harmonized Protocol [1] are required to accommodate this new experience. However, the additional experience shows a need, and provides a basis, for refinement of our approach to many aspects of proficiency testing and for more specific and definite recommen- dations in some areas. Further, the original Harmonized Protocol was largely concerned with the or- ganization of proficiency testing schemes, and is therefore addressed mainly to providers of schemes. The increased importance of proficiency testing scheme data has, however, generated a need for addi- tional guidance on the interpretation of results of schemes by both scheme participants and “end-users” of analytical data (such as laboratory customers, regulators, and other stakeholders in laboratory qual- ity). All these factors call for an update of the 1993 Harmonized Protocol.

    The revision also provides an opportunity to point out that some important aspects of proficiency testing remain incompletely documented at this time. In addition, we must recognize that the variety of possible approaches featured in the ISO documents is intended to be comprehensive and to cover all fields of measurement. Practical experience in chemical analysis strongly suggests that a restricted sub- set from this wide range of approaches provides an optimal approach for routine analytical work. This updated Harmonized Protocol is, therefore, not merely a collation of extracts from other documents, but an optimal subset of methods, based on detailed practical experience of managing proficiency testing schemes, interpreted specifically for analytical chemistry, and incorporating the newest ideas.

    Producing an updated Protocol further allows us to emphasize the importance of professional judgement and experience both for the provision of proficiency testing schemes and for the participants in acting appropriately upon the results. Adherence to a protocol obviously implies that certain actions must be carried out. But the means by which they are carried out needs to be contingent to some extent on the particular application, and the range of possible applications is both large and changing with time. Further, any experienced analytical practitioner will readily recognize that real-life test materials and methods in the rapidly changing field of analytical chemistry will invariably generate occasional unexpected behavior that demands expert consideration and vigilance. Thus, we regard it as unsafe to exclude all scope for expert judgement and to replace it with inflexible rules. The structure of this doc- ument reflects that philosophy. The Protocol proper comes first and comprises a series of relatively short sections outlining the essential actions required for schemes claiming to adhere to it. This is fol- lowed by a number of longer sections and appendices that discuss the o

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