Accreditation and Quality Assurance最新文献

Limited information was available on the quality and safety profile of tea in China, even though food quality and safety of tea is an issue of great concern to consumers and the public. Stochastic Bayesian modeling was employed in this study to investigate food quality and safety profile of tea in China market. Results indicated that the overall nonconforming rate (95 % CI, confidence interval) of tea was 2.6 ‰ (1.3 ‰ to 4.5 ‰), indicating a high level for the quality and safety status of tea in market. Pesticide residues exceeding maximal limit (MRLs) was the major cause leading to nonconformity of tea, with estimated incidences (95 % CI) of 11.7 ‰ (0.5 ‰ to 53.2 ‰), 1.1 ‰ (0.4 ‰ to 2.0 ‰), 2.3 ‰ (0.6 ‰ to 5.5 ‰), and 0.55 ‰ (0.06 ‰ to 1.51 ‰), respectively, for Yellow tea, Green tea, and Oolong tea; whereas illegal application of additives was more likely to occur in black tea, with an incidence of 1.1 ‰ (0.4 ‰ to 2.7 ‰), despite that an estimated incidence of 2.9 ‰ (0.4 ‰ to 16.1 ‰) was generated for Yellow tea due to fewer inspects and small sample sizes involved for analysis. The difference in quality and safety status of tea between provinces was statistically insignificant, as indicated by overlapped 95 % CIs of nonconforming rates. Results of this study provided reliable information on quality and safety profile of tea in China market, and suggested that application of pesticides during tea plantation and illegal use of additives during black tea production worth more attention in respect of quality and safety of tea.

The use of certified reference materials (CRMs) is essential for laboratories that want to achieve reliable results because these materials have well-defined property values that enable the traceability of certain parameters in several areas. The production of CRMs for microbiological tests is complex, as there is a natural instability of microorganisms. The objective of this study was to establish Cryptococcus neoformans and Cryptococcus gattii as CRM, according to the requirements of ISO 17034. The availability of these materials will assist in the cryptococcosis diagnosis and support the academic community, since cryptococcosis is among the most lethal mycoses and affects more than one million people worldwide each year. C. neoformans CFRVS CRM 40,323 and C. gattii CFRVS CRM 40,324 batches, in skim milk at 20 %, were homogeneous and stable for 1 year. The materials were also stable at 4 °C, 25 °C and 35 °C, temperatures that simulate transportation conditions, for 7 days. In addition to the quantitative characterization, qualitative characterization of materials was conducted by observing melanin production, l-Canavanine Glycine Bromothymol Blue (CGB) Agar test and by RFLP-URA5 analyses. Certified property values and their associated uncertainties were assigned for each CRM. For C. neoformans CFRVS CRM 40,323, expanded uncertainty (U_CRM) was 13 CFU mL⁻¹ for 33 CFU mL⁻¹ property value. For C. gattii CFRVS CRM 40,324, U_CRM was 9.2 CFU mL⁻¹ for 15 CFU mL⁻¹ property value. Our study contributes to the development of CRM production in the microbiological field, whose supply is still very limited worldwide.

Electrolytic conductivity is recognized as one of the parameters to determine water quality. An accurate measurement of electrolytic conductivity of wastewater before dumping it into the environment is crucial to prevent water pollution. Therefore, the ability of laboratories in conducting accurate and comparable measurements of electrolytic conductivity is important to guarantee the measurement results. The measurement quality of the laboratories can be determined by participating in a proficiency testing (PT) conducted by accredited PT provider. In 2018, Chemical Metrology Laboratory, Indonesian Institute of Sciences (LIPI), as a PT provider, conducted a PT for electrolytic conductivity measurement with synthetic wastewater as the PT test item. It was prepared from cations and anions commonly found in natural wastewater. A total of 25 participants from Indonesian testing laboratories reported their electrolytic conductivity measurements. These results were then evaluated using a standardized performance statistic of z score, z′ score, E_n score and ζ (zeta) score. There were 20 laboratories having satisfactory results evaluated using both z score and z′ score, while only 14 laboratories were considered having a successful performance evaluated using E_n score and ζ score. The evaluation results show that the participants already have the ability to measure the electrolytic conductivity value but some of them still need improvement in estimating the uncertainty.

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.