Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.15, #12)
Standardized GC–MS (EI) procedure for monitoring the detection and identification performance applied to herbal remedies by Thomas J. Mahier; Inaam I. Al-Doush; Athraa K. Al-Sheikh; Mohammed Al-Tufail; Maciej J. Bogusz (pp. 659-664).
A procedure for monitoring the identification performance of GC–MS instrumentation as applied to herbal remedies was established, using eugenol (extracted from cloves) as a control compound. The following parameters were monitored: retention time (acceptable variability 0.5%); signal-to-noise ratio (at least 40% of the initial value); ion intensity ratio (acceptable variability 20%); and identity search result (reverse match, with minimum match value of 850 for quadrupole instruments and 800 for ion trap instrument). Other candidates for control compounds (pulegone, caffeine, and methoxsalen) as well as other parameters (relative retention time, second ion intensity ratio, peak area, and direct match) did not give any additional information concerning variability, observed trends, and sensitivity.
Keywords: GC–EI–MS; Detection capability; Herbal remedies; Quality assurance
Estimation of uncertainty in measurement of boron in Zr–Nb alloy samples by BF4 − ion selective electrode by P. S. Ramanjaneyulu; K. L. Ramakumar; Y. S. Sayi (pp. 665-671).
Boron doped zirconium–niobium alloy is employed for neutron reactivity control in advanced nuclear reactors. An accurate knowledge of the boron content and uncertainty associated with the measurement result is essential for reactivity calculations. In view of the refractory nature of the alloy, boron determination in these matrices is a challenging task for analytical chemists. Also due to non-availability of matrix-matched reference materials, direct solid analysis cannot be resorted to. With this in view, a simple and sensitive method based on potentiometric determination of boron as tetrafluoroborate with tetrafluoroborate ion selective electrode has been developed. After dissolving the sample, boron was quantitatively converted to BF4 − with the addition of HF. Potential response was measured with Orion 9305 BN BF4 − ion selective electrode. The response of the ion selective electrode was Nernstian in the range of 0.1–100.0 μg/g of boron in the solution. The method has been validated by two independent methods namely spectrophotometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES). All identifiable sources of uncertainties in the methodology have been individually assessed. The combined uncertainty is calculated employing uncertainty propagation law. The expanded relative uncertainty in the measurement (coverage factor 2) is 6.50%.
Keywords: Boron determination; Zirconium–niobium alloy; Tetrafluoroborate ion selective electrode; Estimation of uncertainty
Water content variation of p-n-heptylphenol reference material by Nobuyasu Hanari; Ryoko Iwasawa; Satoko Otsuka; Naomi Fujiki; Ayako Matsumoto; Toshihide Ihara; Keiichiro Ishikawa; Takashi Yarita (pp. 673-679).
Water content variation of candidate p-n-heptylphenol (HP) reference material (ampoule form) for preparation of a primary standard solution based on the Japan Calibration Service System, a national standards dissemination system, under the Measurement Law of Japan, was examined by a Karl-Fischer water content meter. As prepared samples, liquid-phase HP and upper, middle, and lower layers of solid-phase HP were measured since characteristic phase transition occurs near room temperature (melting point: 28.98 °C). As a result of water content in liquid- and solid-phase HP, water content variation among three layers of solid-phase is found in within ampoules, though water content variation of liquid-phase is not found. Between-ampoule variation of water content is also found using total ampoules of liquid-phase HP used to eliminate within-ampoule variation. Moreover, water content variation is secondarily confirmed by the results of the amount-of-substance fraction of HP based on a differential scanning calorimeter. From these results in this study, it is concluded that within- and between-ampoule variations of water content may depend on phase transition and water loss during ampouling of candidate reference material, respectively.
Keywords: p-n-heptylphenol; Japan Calibration Service System; Water content variation; Phase transition; Within-ampoule; Between-ampoule; Reference material; KFT; DSC; GC-FID; GC/TOFMS
Implementation of a quality management system in university test laboratories: a brief review and new proposals by Inês Hexsel Grochau; Carlos Arthur Ferreira; Jane Zoppas Ferreira; Carla Schwengber ten Caten (pp. 681-689).
Quality management systems are difficult to implement in university laboratories involved in teaching activities, R&D and provision of testing services, because of their peculiar characteristics. Testing services are not a priority, the performance of professionals is measured based on their teaching activities and publications, and the laboratories are shared with research and teaching activities. Hard efforts were made all around the world to overcome some of these difficulties. This paper analyzes the process of implementing a quality management system according to the ISO/IEC 17025 standard at two laboratories of the Federal University of Rio Grande do Sul, in Brazil. Some new solutions to solve the main problems typically originated on this type of environment are presented and compared with reports from the literature. It was concluded that it is perfectly possible for university laboratories to have their tests accredited according to standard ISO/IEC 17025, respecting their peculiarities and adopting creative solutions that meet the characteristics and the needs of each institution.
Keywords: Quality management system; University analytical laboratory; Test laboratory
Comparability of measurement results for pesticide residues in foodstuffs: an open issue? by Ricardo J. N. Bettencourt da Silva; Maria Filomena G. F. C. Camões (pp. 691-704).
The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way of ensuring comparability of measurements in this field.
Keywords: Metrological comparability; Metrological traceability; Measurement uncertainty; Pesticide residues; Foodstuffs
Calibration, handling repeatability, and the Maximum Permissible Error of single-volume glass instruments by Veronika R. Meyer; Josef Pfohl; Burkhard Winter (pp. 705-708).
The influence quantities for the uncertainty of a volumetric operation with glass instruments are calibration, repeatability and temperature. In the literature, measurement uncertainty budgets can be found, which count all three quantities separately although calibration and repeatability are merged in tabulated data to the Maximum Permissible Error. We propose that this error should be handled as a rectangular distribution in order to get a standard uncertainty. For the daily use in an analytical laboratory, the combined standard uncertainty of a volumetric operation is thus calculated from the Maximum Permissible Error plus the uncertainty of the temperature influence.
Keywords: Glass volumetric instruments; Maximum Permissible Error; Measurement uncertainty; Measuring flasks; Pipettes; Single-volume glass instruments; Uncertainty of volumetric operations