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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.6, #2)
Introduction to the proceedings of the International Conference on Metrology – Trends and Applications in Calibration and Testing Laboratories, 16–18 May 2000, Jerusalem, Israel
by Ilya Kuselman (pp. 54-54).
Traceable measurements of pH by Petra Spitzer (pp. 55-60).
The primary method for pH is based on the measurement of the potential difference of an electrochemical cell containing a platinum hydrogen electrode and a silver/silver chloride reference electrode, often called a Harned cell. Assumptions must be made to relate the operation of this cell to the thermodynamic definition of pH. National metrology institutes use the primary method to assign pH values to a limited number of primary standards (PS). The required comparability of pH can be ensured only if the buffers used for the calibration of pH meter-electrode assemblies are traceable to these primary pH standards. To assess the degree of equivalence, comparisons of primary measurement procedures for pH were organized in co-operation with EUROMET. Typical results will be presented. In 1998, the Consultative Committee for Amount of Substance (CCQM) decided to include the field of pH in its working programme. The first key comparison for this quantity was recently carried out on two phosphate buffer solutions.
Keywords: Keywords Metrology in chemistry; Traceability; pH; Key comparison
Analysis of long-term distributions of calibration parameters and calibration intervals for an atomic absorption spectrophotometer by I. Kuselman; Irena Goldfeld; Boris Anisimov (pp. 61-65).
A combination of "black box" and "calendar-time" methods for the determination of calibration intervals of an analytical measuring instrument is discussed. Since the methods require information on the distributions of the calibration parameters, such information is described for an atomic absorption spectrophotometer, as an example. The hypotheses on the normal distribution of the calibration parameters are tested using the ω2-criterion and accepted at 0.90–0.95 levels of confidence. Corresponding control charts are designed for indication of warning and action limits of the calibration parameters, and diagnoses of outliers in further calibrations. Control charts indicate also when the calibration should be done according to the full program of the equipment manufacturer.
Keywords: Keywords Calibration parameters; Measuring instrument; Spectrophotometry; Long-term distributions; Control charts; Calibration intervals
Proficiency testing on the analytical control of precious metal production by Yuri A. Karpov; Natella A. Arakelian; V. E. Kvin; Vasilisa B. Baranovskaya; Tatyana Yu Alekseeva; V. P. Obresumov; Lyudmila P. Zhitenko (pp. 66-71).
Our experience of executing proficiency testing programs on the analysis of precious metals and precious metal bearing materials is summarized. Six proficiency testing programs of the ”distributed sample testing” type were carried out using samples essentially distinct from each other: (I) certified samples of fine gold and fine silver, and (II) recoverable raw (scrap and catalyst waste) containing precious metals of unknown contents. The test results were assessed using the London Bullion Market Association (LBMA) rules and by Z-criteria using the ISO/IEC Guide 43 scale. Satisfactory results were presented by all participants for the analysis of certified samples of fine gold and fine silver. The results of catalyst waste analysis agreed rather well, whereas the scrap analysis revealed an essential discrepancy in the data for some samples. The reasons for such discrepancies are discussed.
Keywords: Keywords Proficiency testing; Precious metals; Recoverable raw containing precious metals; Analysis quality
Quality in (analytical) R&D – ideas for the next step after EURACHEM/CITAC Guide 2 by Karl Cammann; W. Kleiböhmer (pp. 72-73).
The EURACHEM/CITAC Guide 2 is an important step towards the establishment of a quality assurance system in analytical research and development. But it is only the first step because it focuses on the metrological characteristics. In addition to Guide 2 there should be a supplementary guide providing assistance for effective and quality-orientated management of research groups.
Keywords: Keywords EURACHEM/CITAC Guide 2; Quality assurance in Research and Development; Analytical results; Quality management
Traceability and uncertainty – A comparison of their application in chemical and physical measurement by Alex Williams (pp. 73-75).
Establishment of the traceability and the evaluation of the uncertainty of the result of a measurement are essential in order to establish its comparability and fitness for purpose. There are both similarities and differences in the way that the concepts of traceability and uncertainty have been utilised in physical and chemical measurement. The International Committee of Weights and Measures (CIPM) have only in the last decade set up programmes in chemical metrology similar to those that have been in existence for physical metrology for over a century. However, analytical chemists over that same period have also developed techniques, based on the concepts of traceability and uncertainty, to ensure that their results are comparable and fit for purpose. This paper contrasts these developments in physical and chemical metrology and identifies areas where these two disciplines can learn from each other.
Keywords: Keywords Traceability; Measurement uncertainty; Chemical metrology; Physical metrology
Metrology for chemical engineers by K. Heydorn; Elo Harald Hansen (pp. 75-77).
The first full-semester course on Quality Assurance in Chemical Measurement was held at the Technical University of Denmark from September to December 1999. The course required sufficient knowledge of basic statistics to understand and apply the methods recommended in ISO 5725–1/6 Accuracy of Measurement Methods and Results. The main purpose of the course was, however, to familiarize PhD students with the BIPM philosophy, using the International Organization for Standardization (ISO) Guide to Expression of Uncertainty in Measurement, which was accepted by IUPAC and other international scientific organizations in 1993. Chemists are notoriously reluctant to accept the BIPM philosophy, but the appearance of a new Draft Guide Quantifying Uncertainty in Analytical Measurement at the EURACHEM Workshop in Helsinki in June 1999 stimulated us to make an attempt to overcome such chemical prejudice. After thorough reading of the examples presented in the Draft Guide, each of the participating students had to prepare an uncertainty budget for their own particular project and present it to the other participants for discussion. Eventually the students learned how to verify their uncertainty budgets by means of experimental results; this invariably entailed a re-evaluation of the uncertainty components in the original budget. The revised budget was again verified, and this iteration was continued until the budget correctly predicted the uncertainty of individual results covering the whole range of applicability of the analytical method. The paper presents the detailed structure of this first course, as well as improvements in the next course scheduled for the year 2000.
Keywords: KeywordsMetrology; Quality assurance; Chemistry; PhD course; Uncertainty
Evaluation of proficiency testing results taking into account their uncertainties by I. Kuselman; Ioannis Papadakis; Wolfhard Wegscheider (pp. 78-79).
A new composite score for the evaluation of performance of proficiency testing participants is proposed. The score is based on a combination of the z-score, uncertainty of a participant’s measurement result and uncertainty of the proficiency testing scheme’s assigned value. The use of such a composite score will allow evaluation not only of the participant’s ability to determine an analyte in corresponding matrix, but also their understanding of the uncertainty in the obtained analytical result. The score may be helpful for the laboratory’s quality system and for laboratory accreditation according to ISO 17025.
Keywords: Keywords Proficiency testing; Uncertainty estimation; Evaluation of performance; z-score; Statistics
MESURA 2000: a strategy to integrate a true communication network of metrology experts with process technology experts by S. Echeverría-Villagómez; Y. Mitani-Nakanishi; H. Nava-Jaimes (pp. 80-84).
The Centro Nacional de Metrología (CENAM) has developed the MESURA Interinstitutional Network in collaboration with other research and development institutes in Mexico. This network has the aim of providing integral metrological services to industry throughout the country, with uniform standards of quality and consistency. The fulfillment of this aim has been possible because of a number of factors that have made the MESURA Program an attractor for the integration of metrological services. Among these factors are: an unswerving focus on the customer needs, an integral and logical problem solving approach to consultancy, adequate modular classification of the consultants functions, clear-cut definition of the functions of each member of interdisciplinary groups, and a uniform code of communication among the members of the network. The next stage of the strategy is to strengthen the link between metrology and its industrial applications forming a new type of consultant with the technical experts from R&D Centers. These will be consultants with general knowledge and experience in metrology, specialized in certain type of industrial processes and products. The strategy will be initiated in the year 2000 and with it the MESURA Network is expected to make a strong contribution to fostering the optimum use of metrology in industry and to act as a channel for the integration of other technologies in which the participating Centers have expertise.
Keywords: Keywords Metrology; Integral metrological services; Quality assurance; Consultancy; Technology administration
Reference materials for the radionuclide program – performance evaluation samples by Edmond J. Baratta (pp. 84-86).
The U.S. Food and Drug Administration's (FDA) Radionuclides in Food Program was reinstituted in 1973, expanded in 1975 and again in 1990, to its present status. The need for reference materials for radionuclides in food samples was recognized as early as 1962. There were no available reference materials for these types of samples at that time. The materials developed to assure that the results being obtained were acceptable were primarily milk, water and food. The radionuclides of interest were iodine-131, cesium-137 and other short-lived radionuclides found in fission products. These were first issued through the then Health, Education and Welfare Department's Analytical Quality Control Program and, later, in 1970 through the Environmental Protection Agency (EPA). In November 1998, the EPA discontinued this program. The FDA is proposing to reinstitute part of this program, as a primary laboratory, traceable to the National Institute of Technology (NIST) and included in this, the FDA proposes to supply the States and/or their contractors with low-level standards and with milk- and water intercomparison samples. It will also use these results where possible as collaborative studies to validate some of the more recent methods adopted by the American Society for Testing and Materials (ASTM), American Public Health Association (APHA) and Association of Official Analytical Chemists International (AOAC, Int'l.) The FDA will also supply low-level standards to compliment these programs as did the EPA. It is expected that these samples will serve as performance evaluation samples for the States programs.
Keywords: Keywords Reference materials; Radionuclides; Food samples