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This paper presents the development of a highly precise and accurate analytical method for the determination of three matrix-bound
pyrethroids, namely, cypermethrin, permethrin, and bifenthrin, using an isotope dilution gas chromatography/mass spectrometry
technique. Identification of the analytes was confirmed under selective ion monitoring mode by the presence of two dominant
ion fragments within specific time windows and matching of relative ion intensities of the ions concerned in samples and calibration
standards. Quantitation was based on the measurement of concentration ratios of the natural and isotope analogues in the sample
and calibration blends. Intraday and interday repeatabilities of replicate analyses of the pyethroids in an apple juice sample
were below 0.5%. The expanded relative uncertainty ranged from 3 to 6%, which was significantly lower than the range obtained
using internal or external calibration methods. As a labeled analogue is not available for bifenthrin, bifenthrin was determined
using labeled cis-permethrin as the internal standard. The results were counterchecked by a gas chromatography-electron capture detection technique
using PCB 209 as the internal standard. The method developed was applied to a recent pilot study organized by CCQM and the
results were consistent with those of other participants. 相似文献
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Accreditation and Quality Assurance - As a result of the changes to the ISO 9001 in 2015, integration of risk-based thinking into the quality management system is going to be a new requirement in... 相似文献
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Siu-kay Wong 《Accreditation and quality assurance》2011,16(11):539-544
Proficiency testing (PT) is an essential tool for laboratories to assess their competency. Also, participation in PT has become
one of the mandatory requirements for laboratory to seek accreditation according to ISO/IEC 17025. For this reason, the effectiveness
of performance evaluation by PT scheme is of great concern for the participants and for accreditation bodies as well. In practice,
owing to unavailability of other appropriate alternatives, PT scheme providers may have to choose using consensus values to
evaluate the performance of participants. However, such consensus values approach was not recommended by relevant international
guidelines for PT schemes with limited number of participants. With the use of Monte Carlo simulation technique, this study
attempted to investigate the effectiveness of using consensus values for performance evaluation in PT schemes with limited
number of participants. The simulation process was schemed according to the statistical model provided by ISO 5725-1 for laboratory
measurement results, which covered components like method bias, laboratory bias, and measurement precision. The effectiveness
of the consensus value approach was expressed as the percentage of participants in a simulation run could get the same evaluation
result, either satisfactory or unsatisfactory, against the “true value.” The findings indicated that the number of participants,
choice of consensus values, mass fraction of analyte, method bias, laboratory bias, and measurement repeatability of participating
laboratories would all affect the effectiveness of the consensus value approach but at different extent. However, under certain
circumstances, use of consensus value could still be considered as an acceptable approach for performance evaluation even
the number of participants was limited. Some of the findings were further verified using real data from PT schemes where appropriate
certified reference materials or reliable reference values were available. 相似文献
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Purity assessment for high-purity organic substances is regarded as one of the core competences of national metrology institutes. For this reason, Consultative Committee for Amount of Substance??Metrology in Chemistry (CCQM) regularly organized intercomparison studies to compare and demonstrate the degree of equivalence of national measurement capabilities for purity determination. This paper reports the method development work for the participation in a recent CCQM key comparison on purity assessment for estradiol. An indirect consecutive estimation approach was adopted to determine the purity of the estradiol sample, i.e., through the identification and quantification of all possible impurities present in the sample. In the course of assessment, a variety of analytical techniques were applied. The most challenging part was to identify and estimate the amount of unknown organic-related substance present in the testing material. For the moisture determination, a gas chromatography with thermal conductivity detection (GC?CTCD) method was employed to supplement the results obtained using coulometric Karl Fischer titration technique. Inorganic impurities and volatile organic compounds residual were analyzed using inductively coupled plasma mass spectrometry (ICP?CMS) and gas chromatography?Cmass spectrometry (GC?CMS) techniques, respectively, and their contributions were found to be comparatively insignificant. 相似文献
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Yiu-chung YipAuthor Vitae Siu-kay WongAuthor Vitae 《Trends in analytical chemistry : TRAC》2011,30(4):628-640
This review evaluates commonly used methodologies for assessing the chemical purity of organic reference materials. Direct assay of the principal component can be established by methodologies such as gas chromatography, liquid chromatography (LC), quantitative nuclear magnetic resonance (NMR), elemental analysis and titrimetry. Measurements of detectable impurity components mainly include determination of water or moisture content, and analysis of residual solvents, and organic and inorganic impurities. To complete assessment of chemical purity, it is necessary to determine the enantiomeric purity of chiral organic reference materials. Promising methodologies for analysis include LC with chiral stationary phases, capillary electrophoresis using chiral selectors, and NMR with chemical-shift reagents. 相似文献
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