Primary reference materials and traceability chain for gas composition

This article briefly describes research on the development of primary reference gases and the traceability system of gas measurement at the National Research Center for Certified Reference Materials, China.     

Considerations of comparability and traceability for food analysts

Presented at the CCQM Workshop on Comparability and Traceability in Food Analysis (18–19 November 2003, BIPM, Sevres, France), consideration is given to the interpretation of comparability and traceability to food analysis. The difficulties and complexities of food analysis are discussed and a case is made for how the principles of comparability and traceability may be used to ensure high levels of analytical quality.Presented at the CCQM Workshop on Comparability and Traceability in Food Analysis, 18–19 November 2003, BIPM, Sèvres, France.     

Mineral oil content in sediments and soils: comparability, traceability and a certified reference material for quality assurance

The performance of twelve laboratories with previously established proficiency in the determination of the mineral oil content in a fresh water sediment is described. The summation parameter total petrol hydrocarbon (TPH) is defined according to ISO 16703:2004 with regard to the sample preparation to be applied, the flame ionisation detection (FID) and the boiling range of C₁₀–C₄₀ to be integrated. Comprehensive tests of homogeneity and stability have been carried out on the candidate material using appropriate models. The outcome of the study served as the basis for the certification of the candidate reference material as ERM-CC015a. The certified mass fraction is 1,820±130mgkg⁻¹and traceability was established by using an appropriate calibration standard certified for the mass fraction of C₁₀–C₄₀. The interlaboratory scatter of measurement results in this exercise can largely be explained by the variability of the individual calibrations based on this common calibration standard.     

The use of certified reference materials in the Romanian traceability scheme

 For ensuring the traceability and uniformity of measurement results, the main objectives of national metrology programmes in chemistry are to calibrate and verify measuring instruments, to evaluate the uncertainty of measurement results and to intercompare the analytical results, etc. The concept of traceability has developed recently in chemical measurements, thus, an attempt to implement the principles of metrological traceability especially by appropriateness calibration using composition certified reference materials (CRMs) is underlined. Interlaboratory comparisons are also a useful response to the need for comparable results. The paper presents some aspects and practices in the field of spectrometric measurement regarding the metrological quality of the traceability by calibrating the instruments using suitable and reliable CRMs. The uncertainty of results, as a measure of the reliability that can be placed on them, has been adequately described in different documents and, as a consequence, some examples of evaluating the measurement uncertainty are described. The relationship between uncertainty and traceability, as two fundamental concepts of metrology which are intimately linked, is underlined. Received: 12 November 1999 / Accepted: 10 December 1999     

Allergen determination in food: reference materials and traceability of results

Food allergens are more or less denatured mixtures of non-defined proteins in complex matrices. The most common technique to measure these proteins is an antibody-based system as, e.g., a commercial ELISA system which consists of an extraction procedure, suitable antibodies and a calibrator. Until now, only a few attempts to standardize these different ELISA systems were performed and the most promising way seems to be a standardization of the calibrator. It is shown that we have currently no methods to fully characterize these calibrators, which are always complex protein mixtures. This also means that the production of reference materials containing these calibrators is not possible. It is proposed to choose a different way because we will never have an unbroken traceability chain. As described in ISO 17511:2003 for the clinical area, one possibility could be the selection of a commercial preparation (e.g. skim milk powder) to which all test kit manufacturers will relate their results on and in a second step to select a reference method.     

The CCQM and comparability and traceability in food analysis

Comparability of the results of food analysis is essential for reliable and uniform interpretation of legal requirements on food safety, for avoiding false tests, fostering fair trade, an equal economic playing field and taking away non-tariff barriers to trade. Global comparability can only be achieved through traceability to internationally agreed common and long-term stable references, being the International System of Units (SI). The Comité International des Poids et Mesures Mutual Recognition Arrangement (CIPM MRA), signed and operating under the intergovernmental treaty of the Metre Convention, is the basis for international recognition and acceptance. The Comité Consultatif pour la Quantité de Matière métrologie en chimie (CCQM) is the committee under the CIPM organizing the technical scientific work establishing worldwide traceability and comparability underpinning the CIPM MRA. The CCQM cooperates with all intergovernmental and international organizations concerned.Presented at the CCQM Workshop on Comparability in Food Analysis, 18–19 November 2003, BIPM, Sèvre, France.     

Review of neutron activation analysis in the standardization and study of reference materials, including its application to radionuclide reference materials

Summary Neutron activation analysis (NAA) plays a very important role in the certification of reference materials (RMs) and their characterization, including homogeneity testing. The features of the method are briefly reviewed, particularly aspects relating to its completely independent nuclear basis, its virtual freedom from blank problems, and its capacity for self-verification. This last aspect, arising from the essentially isotopic character of NAA, can be exploited by using different nuclear reactions and induced nuclides, and the possibility of employing two modes, one instrumental (nondestructive), the other radiochemical (destructive). This enables the derivation of essentially independent analytical information and the unique capacity of NAA for self-validation. The application of NAA to quantify natural or man-made radionuclides such as uranium, thorium, ²³⁷Np, ¹²⁹I and ²³⁰Th is discussed, including its advantages over conventional radiometric methods, and its usefulness in providing independent data for nuclides where other confirmatory analyses are impossible, or are only recently becoming available through newer atom counting techniques. Certain additional, prospective uses of NAA in the study of RMs and potential RMs are mentioned, including transmutation reactions, creation of endogenously radiolabelled matrices for production and study of RMs (such as dissolution and leaching tests, use as incorporated radiotracers for chemical recovery correction), and the possibility of molecular activation analysis for speciation.     

Improvements in efficiency of production and traceability for certification of reference materials

Issues of current interest to certified reference material producers are addressed. Alternative strategies for certification of matrix reference materials are discussed and the benefits of adopting a flexible, cost-effective approach are described. The difficulty of undertaking homogeneity testing where certification is to be carried out with definitive techniques capable of providing very small measurement uncertainty is discussed. Methodology is described which combines conventional screening of the candidate material for homogeneity with an additional, precise assessment of homogeneity based on isotope dilution mass spectrometry measurements. A systematic procedure for evaluating the commutability (horizontal traceability or scope) of matrix reference materials has been evaluated and shows that in some circumstances matrix effects may be less pervasive than is generally believed. This offers the possibility, especially for trace analysis applications, of more efficient use of existing reference materials without compromising measurement reliability. Vertical traceability of matrix reference material data is of growing interest but is difficult to achieve with present interlaboratory certification exercises. A modification is described which attempts to address this issue. It also offers the possibility of improved identification of outliers and reduced variation of data between the participating laboratories.Presented at BERM-9—9th International Symposium on Biological and Environmental Reference Materials, 15–19June 2003, Berlin, Germany     

The role of reference materials

 In this article the role of reference materials is confined to chemical measurements only. Recognized reference materials are one of the tools to obtain comparability of analytical results. Recognition demands confidence in the reference materials and in the reference material producers. A reference material producer is a technical competent body that is fully responsible for the certified or other property values of the reference material. The "analyte" has to be specified in relation to the selectivity of analytical procedure. The full range of reference materials can be presented as a three-dimensional space of the coordinates: analyte, matrix and application. If reference materials are used for calibration or correction of calibrations they establish the traceability of results of chemical measurements. The traceability is only valid within a stated range of uncertainty. Pure substances can represent the unit of amount of substance. A precondition is the microscale specification of the analyte and the accurate determination of the main component and/or the impurities.

     

The role of reference materials

In this article the role of reference materials is confined to chemical measurements only. Recognized reference materials are one of the tools to obtain comparability of analytical results. Recognition demands confidence in the reference materials and in the reference material producers. A reference material producer is a technical competent body that is fully responsible for the certified or other property values of the reference material. The "analyte" has to be specified in relation to the selectivity of analytical procedure. The full range of reference materials can be presented as a three-dimensional space of the coordinates: analyte, matrix and application. If reference materials are used for calibration or correction of calibrations they establish the traceability of results of chemical measurements. The traceability is only valid within a stated range of uncertainty. Pure substances can represent the unit of amount of substance. A precondition is the microscale specification of the analyte and the accurate determination of the main component and/or the impurities.     

A new traceability scheme for the development of international system-traceable persistent organic pollutant reference materials by quantitative nuclear magnetic resonance

Quantitative nuclear magnetic resonance (qNMR) was used for the purity determination of neat compounds of persistent organic pollutants (POPs). qNMR is a unique quantitative method that is not only traceable to the International System of Units (SI), but it also does not require a standard of its own. The purities of the POP compounds determined in this work were traceable to a single certified reference material (CRM), which is extremely attractive for reference material producers. The purities observed by qNMR were equivalent to those observed by gas chromatography with flame ionization detection (GC/FID) or a differential scanning calorimetry (DSC) combined with a thermogravimetric analyzer (TGA). The uncertainties obtained by the qNMR method were comparable to being slightly larger than those observed by DSC.     

Current best practice for traceability in testing laboratories,when certified reference materials are unavailable

Since the implementation of ISO/IEC 17025 in 2002, all accredited laboratories (at the least) need to establish traceability in all their tests and calibration methods. Traceabilty, though well understood in the calibration field (through an unbroken chain of comparisons to the International System of Units —SI), is less straight forward and not so well understood in the testing laboratories. Traceability in analytical and biological testing is found through the use of reference materials, and the validated steps of a test method. This article describes the possibilities to comply with the traceability requirement of ISO/IEC 17025 in testing laboratories , when certified reference materials are unavailable.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, 4–6 November, 2003, Eilat, Israel     

Criteria for the development of biological reference materials

Summary A review is presented of factors to be considered in the development of biological reference materials. Some guidelines are offered regarding approaches to the generation of the varied materials required for analytical quality control. Major considerations in such an endeavour are the goal of the undertaking and role of the final product, selection of candidate materials, preparation, characterization and certification. Selection of materials should be from those important to commerce and consumers, and related to various regulatory, clinical, environmental, and research activities. They should adequately represent the different choices and types of foodstuffs, clinical materials and environmental materials, such as soils, sewage sludges, plant and animal tissues, of interest in different regions of the world.Acquisition can be from commercial sources or the result of in-house preparation, with attention to stability enhancement if required and maintenance of native analyte levels by minimization of contamination. The approach to chemical and physical characterization relies on the measurement philosophy, selection of analytes, their speciation, and selection of analytical methods and analysts for establishment of homogeneity and quantitative levels. Throughout the overall task of RM development there is a requirement for a critical approach by critical analytical and measurement scientists and the involvement of national RM agencies in order to produce top quality control materials.

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Kriterien für die Entwicklung von biologischen Referenzmaterialien

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Contribution No. 88-50 from Land Resource Research Centre     

On the role of environmental reference materials in the development of horizontal standards for environmental protection

The need for standardisation and harmonisation of measurements increases with the progress of the European integration process. One of the areas for which the need for harmonisation has been emphasised is the protection of the soil compartment. While knowledge of problems associated with soils is increasing in Europe, based on soil surveys, monitoring systems and data networks, the corresponding (analytical) data is not often comparable, which limits its value for policy development. In this context, the European Commission has invited the Member States to investigate the possibility for a harmonisation of European standards in the fields of soil, sludge and biodegradable waste (compost). Furthermore, the development of new reference materials for both the validation of these new methods and their successful implementation on a routine basis is required. This paper shows some selected examples for which the development of horizontal standards may be worth investigating. In addition, it discusses and proposes the vehicle of (C)RMs for the implementation of a common measurement system for soil, related to these horizontal standards. It also raises some open questions and sheds light on future perspectives and challenges.Presented at BERM-9 – 9^th International Symposium on Biological and Environmental Reference Materials, June 15–19, Berlin, Germany     

The role of reference materials in the analytical laboratory

Summary Importance, definition, preparation, characterization, selection and use of reference materials in the analytical laboratory are discussed in general.

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Die Rolle der Referenzmaterialien im analytischen Laboratorium

Zusammenfassung Bedeutung, Definition, Herstellung, Charakterisierung, Auswahl und Verwendung von Referenzmaterialien im analytischen Laboratorium werden allgemein diskutiert.

     

Quality control and reference materials in speciation analysis

This contribution describes the need and some strategies for a rigid quality control in speciation analysis. Firstly, the term “chemical speciation” is defined and differentiated from experimental concepts now called “operationally defined speciation” or “functionally defined speciation”. The need for quality control in speciation is given by the big number of sources of errors during sampling, sample preparation, separation and detection. Errors such as stability problems, contaminations or losses, spectral interferences etc. are discussed. On the other hand, several concepts for problem solutions are described. One of these solutions is the use of certified reference materials (CRM). Unfortunately, species-certified CRM are only available for few matrices and few elements, e.g. mercury in fish or sediments, lead in solutions and urban dust etc. Therefore special quality control strategies are necessary for each part of the analytical speciation procedure. Several examples of such procedures are given and discussed. Received: 25 July 1998 / Accepted: 8 August 1998     

A need for clearer terminology and guidance in the role of reference materials in method development and validation

 The fact that various definitions and terminology applied to measurements in analytical chemistry are not always consistent and straightforward, by not only answering the question ”what”, but also ”how”, leads to their various interpretations. This results in non-uniform implementation of very basic and essential metrological principles in chemistry. Such a diverse situation is not conducive to the endorsement of harmonised measurements all across the world, to serve as a tool for improving the quality of life in its broadest sense for all its citizens. The discussion in this paper is focused on problems associated with terminology and definitions of ’reference material’ and ’validation’. The role of reference materials in measurement processes for purposes other than calibration and validation principles in analytical chemistry are also discussed in this paper. Where possible, potential solutions are proposed, but more often, questions of essential importance are raised in order to initiate international discussion which will hopefully lead to equally understandable answers. Received: 2 November 2002 Accepted: 3 February 2003 Acknowledgements   The author is grateful to Aleš Fajgelj for his comprehensive comments on the topic described in this paper. Sincere thanks also to Philip Taylor, Ewa Bulska, Emilia Vassileva, Miloslav Suchanek and Margreet Lauwaars for their contribution during fruitful discussions on validation. Presented at the CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to N. Majcen     

Global activities in the world of reference materials including the needs of developing countries

Proceedings of previous BERM meetings have been used to assess emerging trends in the development of RMs to meet AQC requirements of clinical, food, nutrition, and environmental health areas. BRM-1 reflected a strong need to initiate and expand RM activities for certifying organic nutrients in foods. BRM-2 highlighted the distinction between primary (certified) and secondary (e.g. check samples for proficiency testing) RMs¹. BRM-3 identified the need for producing different levels of an analyte in a given matrix (spiked standards) to address matrix related measurement problems in foods. BERM-4 highlighted the need for a global vision in dealing with standards, illustrated by the activities of GESREM. Also, the logistics required for setting up intercomparison programs related to food safety monitoring programs were outlined. BERM-5 presented the changing outlook of the AOAC International in recognizing the usefulness of incorporating RMs for use in conjunction with their methods validation protocol. BERM-6 brought to the forefront the concern for traceability of chemical measurements to internationally recognized standards. BERM-7 recognized the need for multidisciplinary approaches for preparing certain types of CRMs, partly in response to the measurement needs arising from governmental regulations dealing with food safety and environmental health criteria. Finally, BERM symposia have promoted a meaningful dialogue on the RM needs of African, Asian and South American countries and provided the developing countries opportunities to discuss their problems with the international analytical community. The issue of health safety is involved in movement of foodstuffs between countries, and therefore, international efforts as voiced by the World Health Organization to provide guidance and assistance in AQC matters to the needy countries deserve consideration.     

The role of reference materials in analytical chemistry

The paper demonstrates a concept and possible models for an international infrastructure of chemical measurements by using reference materials.The function of reference materials to establish traceability and means of quality assurance is emphasized.