Accreditation and Quality Assurance最新文献

The Guide to the Expression of Uncertainty in Measurement (GUM) provides a framework for evaluating analytical data and characterizing their dispersion in a consistent manner. This is of eminent importance in the case of reference materials and their recommended values that are used for calibration of further measurements. The proper propagation of uncertainties for those data is essential. Guidance is provided in the GUM on how to calculate the combined standard uncertainty for a mean value or central value based on multiple individual measurements including their calibration uncertainty. However, according to published data, the guidance provided by GUM is not always properly applied in practice. Several published studies show calculated uncertainties much lower than those of input quantities. This may be caused by improper handling of the propagation of uncertainty components, thereby breaking the traceability chain for reported values. A simple check method using conventional statistical means is proposed to detect and to avoid such mistakes related to calibration uncertainties. It is intended to help to ensure a proper uncertainty propagation, to maintain a system of reliable and traceable reference materials. A spreadsheet is provided for the implementation of such a check. Example calculations for published data are presented.

Some widely used classical tests for homogeneity of variance (Fisher, Link, Cochran, and Bliss–Cochran–Tukey) are considered for the case when the random variable has a symmetric two-side power distribution. The corresponding critical values for the test statistics are obtained. Some comparative analysis of power of the tests is carried out. The case when the null hypothesis assumes a minor random scatter of the variance is considered separately.

Compliance with all the requirements in the ISO/IEC 17025:2017 is crucial for testing and calibration laboratories in assuring the quality of measurement conducted in their laboratories. The latest version of the ISO/IEC 17025:2017 presents a different structure compared to the previous version, ISO/IEC 17025:2005. Therefore, amendments in the quality documents and the operational procedures in the laboratories are urgently required. However, not all laboratories’ personnel understand this new standard and know how to implement or incorporate this new version standard with their old version documents and operational procedures. It causes a problem for the testing and calibration laboratories, especially in Indonesia. This study is expected to provide enlightenment and hints for the laboratories struggling to comply with the ISO/IEC 17025:2017.

This short article discusses the units of rate constants as used in chemical kinetics and, in particular, the aspect of non-integral powers of base units, which some might find unusual for units in the SI system. In many ways the fact that the units of the rate constants as usually defined convey information about the order of the reaction or reactions involved is very useful, but in other ways having the same (or at least very similar) quantity that has different units under different conditions is not so desirable. Furthermore, just as with chemical equilibrium constants, taking functions of the rate constant (such as the logarithm when representing the Arrhenius equation in the form ln (k,{text {vs.}},1/T)) needs special attention. Here we examine a possible alternative definition of rate constants in terms of an explicit ratio to the concentration standard state and although we acknowledge that this approach unlikely to be adopted by the community, it serves as a basis to discuss the meaning of rate constants.

This paper describes the development of an olive oil certified reference material containing benzo[a]pyrene and benz[a]anthracene. A method combining solid phase extraction and gas chromatography-isotope dilution mass spectrometry was used for the assignment of certified values and long-term stability study. The method was demonstrated to be suitable for the value assignment of both polycyclic aromatic hydrocarbons (PAHs) as our result was in good agreement with those from other metrology institutes in an international comparison (CCQM-K146) on determination of benzo[a]pyrene in olive oil. A metrological approach was taken to consider potential biases when certifying the mass fraction values of these two PAHs. The certified values with their associated uncertainties at approximately 95 % confidence level obtained for benzo[a]pyrene and benz[a]anthracene in olive oil were 9.85 µg/kg ± 0.75 µg/kg and 8.05 µg/kg ± 0.48 µg/kg, respectively. The measurement uncertainty was obtained by combining the uncertainty contributions from characterisation, homogeneity and stability of the material. Since the mass fraction levels of PAHs in the CRM are about five times higher than the regulatory limits or quantification limits, the practical use of the CRM is as a positive control for PAH monitoring in edible oil samples.

Proficiency testing schemes by interlaboratory comparisons are used to determine the performance of individual laboratories for specific tests or measurements. The international standard ISO 13528:2015 provides a description of statistical methods used for achieving this goal; one of these methods is the z score. The standard allows each participant to choose a measurement method and this can lead to inhomogeneity between participant variance known as heteroscedasticity. The ISO 13528:2015 standard does not mention heteroscedasticity in its statistical procedures. This paper describes a new approach, based on residuals analysis, to assess the performance of an interlaboratory comparison for determining the presence of benzoic acid in orange juice. The results indicate that the conclusions (using z scores) and the proposed approach are different for some laboratories. This occurs due to violation of the homoscedasticity assumption. The z score procedure does not consider this assumption violation while residual analysis can provide such information. Feasible generalized least squares allow one to deal with non-homoscedasticity.

In the latest revision of the ISO/IEC 17025 standard, General requirements for the competence of testing and calibration laboratories, published in 2017, the concept of risk-based thinking was introduced in its requirements. Although the new version introduces the concept, procedures to be adopted for the implementation of risk management in testing and calibration laboratories are not addressed. The article is conceptual in nature and summarizes information from the literature to assess the application of reputable risk management models and implement them in laboratories. Furthermore, it includes discussions on the implementation of risk management in the daily laboratory operations in a practical and effective way as per the requirements of ISO/IEC 17025.

4-Bromodiphenyl ether is a persistent organic environmental pollutant. It is the metabolism of polybrominated diphenylethers, which are widely used as bromine-based fire retardants. The preparation of certified reference material is of great significance for the related research and detection of bromine-based fire retardants. Characteristics, category and function of 4-bromodiphenyl ether certified reference materials are introduced. Two independent methods, the mass balance method and differential scanning calorimetry method, were optimized and applied to determine the purity value. As a result, the mass fraction was determined to be 0.992 ± 0.006. The process was in accordance with the Acts for Management of Reference Materials, and the 4-bromodiphenyl ether reference material was approved as a grade secondary reference material by the State Administration for Market Regulation of China with the certificated number GBW (E) 084477.

Food allergy is a significant health problem, and food industry is obliged to provide accurate labelling by clearly indicating the presence of some allergens to protect consumers. This issue concerns also winemakers as the EU Commission Implementing Regulation No. 579/2012 of 29 June 2012 establishes that wines treated with allergenic additives or processing aids are subject to specific labelling if their presence can be detected in the final product. The request of analyses of allergens in wines has increased in recent years, and laboratories therefore have a key role to play in this process. The most performed method for detection and quantification of proteins in wine is the ELISA method, thanks to its performances, ease to use and relatively moderate costs of equipment. However, the analysis of allergens in wine remains a challenge for laboratories, which can choose from an increasing number of kits that differ in allergen extraction method and are likely to estimate diverse forms of the researched protein. To allow laboratories to compare their results and to obtain recognition of their analytical procedures by winemakers and accreditation bodies according to the ISO/IEC 17025 standard, regular proficiency-testing schemes (PTS) for the detection and quantification of allergenic proteins in wine have been proposed since June 2014. For each test, the statistical treatment of the laboratories’ results is performed according to ISO 13528. Results obtained in different tests for analyses of casein, ovalbumin and lysozyme on red, white and rosé wines show that these analyses are well managed by laboratories, even if some drawbacks are encountered especially for some matrices whose physico-chemical properties can interact with the searched allergen.