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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.6, #1)
Is comparability no longer about the ability to compare similar or different magnitudes?
by Paul De Bièvre (pp. 1-1).
Metrology in chemistry – a public task by G. Dube (pp. 3-7).
The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods, and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration certificates (CIPM MRA) issued by the NMIs.
Keywords: Keywords Reliability; Uncertainty; Traceability; National Metrology Institutes; CIPM MRA
The analysis of process gases: a review by K. D. Cleaver (pp. 8-15).
A general review of key issues involved in the analysis of process gases is presented. The reasons for such measurements – which include safety, quality, environmental and economic factors are considered. The technical issues arising from these measurements are dependent upon a variety of factors, including the overall sampling system, the type of analytical instrumentation, methods of data collection and the specified calibration protocols. The use of gas calibration cylinders as transfer standards is detailed and issues of stability and traceability to reference material discussed.
Keywords: Keywords Process; Gas; Analysis; Sampling; Traceability
Metrology in laboratory medicine – Reference measurement systems by R. Dybkaer (pp. 16-19).
The medical laboratory must provide results of measurements that are comparable over space and time in order to aid medical diagnosis and therapy. Thus, metrological traceability, preferably to the SI, is necessary. The task is formidable due to the many disciplines involved, the high production rate, short request-to-report time, small sample volumes, microheterogeneity of many analytes, and complex matrices. The prerequisite reference measurement systems include definition of measurand, unit of measurement (when applicable), consecutive levels of measurement procedures and calibrators in a calibration hierarchy, international organizations, reference measurement laboratories, dedicated manufacturers, written standards and guides for the medical laboratory, production of reference materials, internal and external quality control schemes, and increasingly accreditation. The present availability of reference measurement procedures and primary calibrators is shown to be insufficient to obtain international comparability of all types of quantity in laboratory medicine.
Keywords: Keywords Calibrator; Laboratory medicine; Metrological traceability; Reference material; Reference measurement system
Homogeneity and stability of reference materials by T. P. J. Linsinger; J. Pauwels; A.M.H. van der Veen; H. Schimmel; A. Lamberty (pp. 20-25).
Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation to create materials as homogeneous and stable as possible. Degradation can generally be minimised by reducing the water activity of the material to a level between 0.15 and 0.35. However, careful preparation by itself is not enough. Positive demonstration of homogeneity and stability is required from the perspective of implementing uncertainty calculus according to the Guide to the Expression of Uncertainty in Measurement (GUM). In many cases, homogeneity and stability studies fail to give sufficient quantitative information on homogeneity and stability, mainly because of a lack of measurement repeatability and insufficient number of replicates. In this work, some solutions to these problems and their implications are presented.
Keywords: Keywords Uncertainty; Homogeneity; Stability; Certified reference material
Uncertainty calculations in the certification of reference materials. 2. Homogeneity study by A.M.H. van der Veen; T. P. Linsinger; J. Pauwels (pp. 26-30).
Many reference materials undergo a batch certification, which implies that a small number of samples is taken from a batch, characterised, and these results are then assumed to be representative of all remaining samples. An important aspect in this design is the translation of the characterisation data to a single sample, as usually the laboratory will be using only one sample of the batch. This form of homogeneity is very important and can be influenced to a certain extent by well-designed sample preparation procedures. Another subsampling problem associated with many reference materials is that only a small test portion is drawn from the sample to carry out the measurement. Obviously, this test portion must be representative of the sample, otherwise the certified value is still not applicable. Both kinds of homogeneity tests are examined in the paper and evaluated using practical examples.
Keywords: Keywords Reference materials; Measurement uncertainty; Analysis of variance; Homogeneity study; Minimum sample intake
Automated ion-selective measurement of lithium in serum. A practical approach to result-level verification in a two-way method validation by S. Linko (pp. 31-36).
The Quality Assurance Department of Medix Diacor Labservice evaluated a two-way method validation procedure for serum lithium quantification in therapeutic drug monitoring In the process of a company fusion and rationalization of two considerably large production lines, three independent ion-selective electrode (ISE) methods were surveyed, among many others. While tailoring the new medical laboratory production, subcontracting from a collaborating company was discontinued. Likewise, modernization of the ISE instrumentation was unavoidable to increase throughput and effectiveness. It was important that the new result levels should be comparable both with the former subcontractor's levels and with the levels reported from the previously existing instrumentation. The aim of this study was to evaluate the most crucial performance characteristics of a novel lithium method in comparison to the two ISE test methods being withdrawn. The standardized lithium test method was inspected in terms of linear measurement range, analytical variation, bias, past and on-going proficiency testing, in addition to method comparison, to achieve the desired analytical goals. Fulfilling the accreditation requirements in terms of the introduced method validation parameters is discussed.
Keywords: Keywords Validation; Lithium; Performance; Proficiency testing; Analytical goals
Metrology in Chemistry – Workshop at EUROANALYSIS XI, Lisbon, Portugal, 7 September 2000
by I. Papadakis (pp. 42-43).
Chemical aspects of metrology in the chemical industry by R. Schmidt (pp. 48-50).
A brief description is given about the role of metrology in the chemical industry both in production and analysis. Chemical aspects in metrology such as sample stability, homogeneity, cross-contamination, cross-interference not known to other measuring fields have to be taken into account. The measurement carried out to decide about the quality of a chemical product must be fit for purpose. The measurement index (MI) can be used as a readily available key figure for this task. The quotient of the standard deviation of the measurement and the overall standard deviation of the process defines the ability of a given method to monitor process changes for a specific test item. The definition, origin and quality of reference and working calibration substances used are explained. Comparability to the first lab sample and consideration of the customer's needs are of utmost importance in the chemical industry whereas traceability to SI units is normally restricted to the calibration of laboratory equipment.
Keywords: Keywords Measurement index; Measurement uncertainty; Analytical measurements; Traceability; Comparability