TE 1350 web - IAEA Scientific and Technical Publications

IAEA-TECDOC-1350

Development and use of reference materials and quality control materials

April 2003

The originating Section of this publication in the IAEA was: Industrial Applications and Chemistry Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria

DEVELOPMENT AND USE OF REFERENCE MATERIALS AND QUALITY CONTROL MATERIALS IAEA, VIENNA, 2003 IAEA-TECDOC-1350 ISBN 92?0?103303?6 ISSN 1011?4289

? IAEA, 2003 Printed by the IAEA in Austria

April 2003

FOREWORD

The application of certified reference materials (CRMs) in analytical chemistry for quality control purposes is well recognized and recommended by a wide range of international, national and professional organizations. However, irrespective of the geographical region or the economic situation in laboratories, current practice in CRM application in many analytical sectors is not adequate. Therefore, the International Atomic Energy Agency (IAEA) organized a consultants meeting of a group of experts at its headquarters in Vienna in August 2001 to encourage quality assurance and quality control in nuclear analytical laboratories in Member States. This report is a result of the meeting.

The report summarizes current knowledge on correct use of commercially available CRMs and reference materials (RMs), and also acknowledges the limitations and restrictions analysts have to face if they want to apply quality control. For certain matrix types, CRMs might not be available at all, or the range of concentrations and/or analytes needed might not be certified. In many of the analytical laboratories in developing countries lack of financial resources restrict the comprehensive use of available CRMs that are largely prepared and commercialized in western countries. The concept of in-house RMs or quality control materials (QCMs) is advocated to supplement (not substitute) the use of CRMs for quality control purposes. On hand advice on how to select, prepare, characterize and use these QCMs is given from the experts' perspective. Several scenarios are described to make this concept widely applicable to: advanced laboratories with CRMs with validated analytical techniques available, laboratories with less experience and facilities, as well as cases were labile compounds and unstable matrices are involved. Each scenario considers different approaches to overcome the lack of appropriate CRMs and advise on the preparation of QCMs, which might fit the particular purpose.

This publication is intended to assist analytical chemists in their efforts to maintain good quality results and provide them with a tool to overcome situations where QA/QC could not be easily implemented. The report is a contribution to boost quality system implementation and finally encourage nuclear analytical laboratories to prepare themselves for formal accreditation. It is hoped that this initiative will add to the sustainability of nuclear applications in IAEA Member States.

The IAEA wishes to thank all the experts for their valuable contributions and the International Union of Pure and Applied Chemistry (IUPAC) for permission to use the article on Harmonized Guidelines for Internal Quality Control in Analytical Chemistry Laboratories that is annexed to this report.

The IAEA officer responsible for this publication was M. Rossbach of the Division of Physical and Chemical Sciences.

EDITORIAL NOTE

The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA.

CONTENTS

1. INTRODUCTION .................................................................................................................. 1

1.1. Requirements for demonstrated quality in analytical laboratories ................................. 1 1.2. Use of CRMs -- Why and how...................................................................................... 2 1.3. Substitute CRMs for quality control purposes with in-house QCM .............................. 4 1.4. Intended use -- Proper use of QCMs ............................................................................. 6

2. DEVELOPMENT OF QCMs UNDER SCENARIO 1: CRMs AVAILABLE, VALIDATED METHOD UNAVAILABLE......................................................................... 7

2.1. General considerations ................................................................................................... 7 2.2. Availability of validated methods................................................................................... 8 2.3. Material selection ........................................................................................................... 9 2.4. Identification and selection of analytes .......................................................................... 9 2.5. Amount of material....................................................................................................... 10 2.6. Material preparation ..................................................................................................... 10 2.7. Storage .......................................................................................................................... 11 2.8. Physical characterization .............................................................................................. 11 2.9. Chemical characterization ............................................................................................ 11 2.10. Statistical evaluation................................................................................................... 11

3. DEVELOPMENT OF QCMS UNDER SCENARIO 2: VALIDATED METHOD AVAILABLE, NATURAL MATRIX (C)RM UNAVAILABLE ....................................... 12

3.1. Introduction .................................................................................................................. 12 3.2. General considerations ................................................................................................. 12 3.3. Detailed considerations of steps recommended for the development of in-house

RMs/QCMs .................................................................................................................. 13 3.3.1. Discussion of relevant steps ............................................................................... 14 3.3.2. Approaches to the characterization/certification of reference materials ............ 19 3.3.3. General principles of certification ...................................................................... 19 3.3.4. Classification of characterization/certification schemes .................................... 20 3.4. Summary....................................................................................................................... 24 3.5. Conclusions .................................................................................................................. 25 3.6. Example: Recommended sample procedure of assignment of reference concentration values to QCM using multiple methods of analysis............... 26 3.6.1. Analytical method selection and testing............................................................. 26 3.6.2. Specific example (potassium in Wheat Gluten RM NIST RM 8418 ................. 27 3.6.3. Simple paired t-test calculations......................................................................... 34 3.7. The technique of recovery for method verification ...................................................... 36 3.7.1. General considerations for use of recovery materials......................................... 37 3.7.2. Determination of recovery based on added analyte............................................ 39 3.7.3. Calculation of recovery....................................................................................... 41 3.7.4. Differentiation between recovery and bias/systematic error .............................. 42 3.7.5. Application of recovery factors .......................................................................... 43

4. SCENARIO 3: CASE OF UNSTABLE ANALYTES AND/OR UNSTABLE MATRIX........................................................................................................ 43

4.1. Analytes and matrices................................................................................................... 43

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