Accreditation and Quality Assurance最新文献

A simple graphical display is described for investigating agreement among interlaboratory data with reported uncertainties. The plot consists of a measure of agreement—the significance level of a test for significant pairwise difference, adjusted for multiple comparisons—plotted as an image in which significance is represented by colour or intensity. This provides an easily interpretable graphical presentation in which the degree of consensus can be judged and in which anomalies are easily visible. The construction of the plot is discussed, with attention to the choice of adjustment for the size of the data set in checking for anomalies. The advantage over visual inspection using error bars is discussed, and some examples from metrology comparisons are presented.

A sensitive, rapid and reliable method was developed and validated for the quantitative determination of 19 elements (31 elemental isotopes) in drinking water using inductively coupled plasma–mass spectrometry. A commercial drinking water matrix was used for conducting method validation in terms of selectivity, limit of detection, limit of quantification, sensitivity, linearity, working range, trueness, precision and measurement uncertainty. Validation parameters are briefly discussed and assessment criteria have been set. In the case of linearity, residual percentage of all elemental isotopes fell in the acceptance range of 80 % –120 % from the expected concentration, with r² greater than 0.990 except for ⁹⁸Mo, for which r² was 0.986. In terms of trueness, recoveries for all elemental isotopes fell in the acceptable range of 80 %–120 % except for ¹¹B for which recovery was 122 %. In terms of precision, repeatability of the analytical method ranged from 0.45 % for ⁶³Cu to 6.75 % for ⁷⁸Se while in case of within laboratory reproducibility it ranged from 1.07 % for ⁶⁵Cu to 10.53 % for ²⁷Al. In addition, expanded uncertainty ranged from 3.5 % for ⁶³Cu to 24.8 % for ²⁷Al. Traceability of the measurement results was established based on the use of certified ICP Multi-element standard solutions and by analyzing spiked samples. It can be concluded that the described analytical procedures to measure the mass concentrations of 19 elements in drinking water samples with established traceability and evaluated uncertainty can provide reliable and internationally comparable results.

The COVID-19 pandemic posed new and manifold challenges to organizations and their operations worldwide. Conformity assessment bodies (CABs), such as testing or medical laboratories, certification, and inspection bodies, were also affected by the associated disruptions. Their role in this crisis is highly relevant, as CABs are essential pillars of the quality infrastructure: their activities ensure that products and services meet requirements as defined in standards and regulations, thereby contributing to their safety and reliability. The question arises of how CABs and their operations were affected by the pandemic and how they responded. To this end, we present the results of an international survey of 986 CABs of all types in Germany, the UK, Italy, and New Zealand. Overall, CABs reported, on average, a reduction in demand for their services during the pandemic, facing restrictions in all countries. In addition, the pandemic had an overall negative impact on the CABs’ investment and innovation activities. However, investments in digital infrastructure were increased as a countermeasure, with CABs reporting a higher need for digitalization. The paper highlights and discusses results from in-depth analyses relevant to policymakers and industry alike.

Scientific research and consequent progress, leads to the introduction of new concepts, new theories and new experimental methods and procedures. Their implementation, presentation and discussion, bring the associated need to choose and adopt the most appropriate terminology. The choice of the right words, definitions, or descriptions of all kinds, is far from being a minor task, demanding the best knowledge of the experts. As time goes by, this often requires revision and upgrading. In this work, Analytical Chemistry is the chosen scientific discipline, from where relevant examples are being taken and presented. Expression of acidity in terms of pH is addressed, covering a selection of developments where the author has been an active player along half a century, ranging from Chemistry to Metrology, hence involving expertise from both fields. Whilst much has been done, more is needed and continues to happen.

Uncertainty intervals for many measurement results are typically reported as symmetric intervals around the measured value. However, at large standard uncertainties (> approx. 15 %–20 %), it is necessary to consider asymmetry of the uncertainty intervals. Here, an expression for calculating uncertainty intervals handling asymmetry when the relative standard uncertainty is independent of the measurand level is presented. The expression is based on implementation of a power transformation (({x}^{B})) for transformation of measurement results in order to achieve results that have a symmetric and approximate normal distribution. Uncertainty intervals are then calculated in the transformed space and back-transformed to the original space. The transformation includes a parameter, B, that needs to be optimized, and this can be based on real results, modelling of results, or on judgement. Two important reference points are B equal to 1 that corresponds to an approximate normal distribution of the original measurement results, and B approaching 0 that corresponds to an approximate log-normal distribution of the original measurement results. Comparisons are made with uncertainty intervals calculated using other expressions where it is assumed that measurement results have a normal distribution or a log-normal distribution. Implementation of the approach is demonstrated with several examples from chemical analysis.

This paper describes a collaborative effort by five metrology institutes to organise a proficiency testing (PT) programme which aims to evaluate the performance and improve the measurement capabilities of food testing laboratories on additives in food sauce in the Association of Southeast Asian Nations (ASEAN). It was the first joint PT programme organised by the metrology institutes under the auspice of the ASEAN Reference Material Network (ARMN). Five common additives, namely: benzoic acid, sorbic acid, methyl paraben, n-propyl paraben and saccharin in tomato sauce, were chosen as the measurands of the PT programme. Thirty-nine laboratories from five economies participated in this PT programme through the ARMN network. Metrologically traceable assigned values used for performance evaluation of the additives were jointly determined by three metrology institutes using isotope dilution mass spectrometry (IDMS). Issues discussed in the paper include determination of assigned values, performance evaluation, participating laboratories’ analytical methods and evaluation of measurement uncertainties. The overall performance of participating laboratories was considered to be satisfactory as 88 % of the participating laboratories achieved satisfactory z-scores (or z’-scores). The joint ARMN accuracy-based PT programme enables a broader understanding of the comparability of measurement capabilities of the food testing laboratories, which play an important role in supporting trade-related industries among the close trading economies in the Southeast Asian region.

A range of oxygenated volatile organic compounds (OVOCs) are present in the atmosphere as a result of direct emissions and as products of atmospheric oxidation. Long-term measurements are important to understand changes to these emission sources and atmospheric oxidation processes. Accurate and stable traceable gaseous primary reference materials are needed to underpin rigorous quality assurance and quality control at monitoring stations such as those organised by the World Meteorological Organization Global Atmosphere Watch (WMO-GAW) programme. The development of a capability for providing traceable primary reference materials (PRMs) of OVOCs is of paramount importance due to the increasing prevalence of these compounds in the urban atmosphere and also because there is currently no Central Calibration Laboratory (CCL) for these components within the WMO-GAW programme. This EURAMET bilateral comparison demonstrates the measurement compatibility (≤ 3%) for three OVOCs (methanol, ethanol and acetone) at nominally 5 µmol mol⁻¹ between two National Metrology Institutes: the National Physical Laboratory (NPL), UK and the Van Swinden Laboratorium (VSL), the Netherlands. The comparison shows that a gravimetric method for value assignment is applicable to acetone but that a more complicated procedure must be employed to value assign methanol and ethanol due to corrections for adsorption effects, which can be as large as 10 % of the nominal value. This work demonstrates the importance of making appropriate corrections to ensure the accuracy of these reference materials. NPL and VSL used different approaches to make these corrections providing confidence and independent verification. This work supports new calibration and measurement capabilities for methanol, ethanol and acetone in the range of 1 μmol mol⁻¹ –10 μmol mol⁻¹ with expanded uncertainties of 6.9 % (3 %), 7.3 % (3 %) and 1.7 % (2 %) for NPL (VSL), respectively, to be realized in the key comparison database and supports the development of the required traceability infrastructure to underpin long-term global measurements of these OVOCs.

This report describes work to evaluate the performance of different commercial and proprietary cylinder treatments in improving the stability of ammonia reference materials in high pressure cylinders. Gas mixtures of 100 µmol/mol and 10 µmol/mol ammonia in nitrogen were prepared gravimetrically at both NPL and VSL. Comparative measurements at each amount-of-substance fraction were used to assess which passivation technique minimised the loss of ammonia upon preparation. The results indicate little difference between the commercial treatments, except at lower amount-of-substance fractions (10 μmol/mol). The variation observed in performance might be explained by the different abilities of the various treatments to prevent the adsorption of ammonia molecules on the internal surfaces of the cylinder, although the role of residual water on the cylinder surface in reacting with ammonia is unclear.

Measurement uncertainty is a non-negative parameter that characterizes the dispersion of the quantity values attributed to a measurand, based on the information used. This work outlines top-down evaluations of the measurement uncertainty in the analysis of pesticide residues by using precision and bias data. Since 2009, a European Standard for vegetable products has been issued which describes a multi-method for the analysis of pesticide residues in foods of plant origin such as fruits, vegetables and cereals. This method makes testing for hundreds of compounds quick and easy in a single extraction, but technical difficulties nevertheless have arisen in the highly polar pesticides in these specific cases; methods suitable for single pesticide residues are used. Consequently, we defined a workflow to estimate measurement uncertainty depending on method type selection. The calculation of individual Measurement Uncertainty (MU) may not always be possible for multi-residue method; then, an alternative approach was applied to estimate a generic MU using data from different proficiency tests selected for the three main product groups (fruit, vegetable and cereal) in combination with intra-laboratory precision. This approach shows a limitation due to the minimum number of proficiency test results that prevents their effective implementation in single residue methods. Therefore, a specific approach based on internal laboratory quality control for individual pesticides in a specific family group of products on real samples was applied to estimate the Measurement Uncertainty. The Flonicamid residue in vegetable products was the selected case study for the Single Residue Method.

The GUM suite of documents (Guide to the expression of uncertainty in measurement and related documents) has been expanded with the addition of a new guidance document describing the development and use of measurement models for obtaining a value for the measurand and an associated measurement uncertainty. The methods for estimating the measurand and evaluating measurement uncertainty in the GUM suite all hinge upon a measurement model that relates the measurand to a set of input quantities. Many users find the development of these models challenging, and so far little guidance has been made available for how to address this pervasive challenge. In this paper, we show how the new document takes the reader from the specification of the measurand through the steps needed to arrive at a complete measurement model, suitable for providing a value for the measurand and an associated uncertainty. An important intermediate stage in this process is the description of the measurement principle, as for many users of standardized test methods this principle is already described by a model. This “basic model” needs extension to include effects arising from the measurement, such as calibration, corrections to be applied, repeatability and reproducibility. The document also introduces statistical models, which recognise the dispersion of replicated observations of the same quantity while capturing the fact that all are informative about the true value of the measurand. JCGM GUM-6 is a valuable contribution to the GUM suite in that it provides a structured and flexible approach to the creation, validation, and use of measurement models.