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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #5)
Statistical approach to the rational selection of experimental subjects by Pedro Araujo; Livar Frøyland (pp. 185-189).
Whilst human and animal experimentation receives much attention every year by the general media, the public and the scientific community, little has been done on how to reduce the number of living subjects to be submitted to experimental research. Researchers who design human and animal experiments are conscious that trials on such subjects present a problem, which is not only scientific, but also ethical. The national research and ethics committees regulate the selection and number of patients or mammals to be treated and make the justification of the number of living subjects an aspect of paramount importance in different scientific disciplines. However, a rational methodology to estimate a sensible number that is in accordance with the parameters of the Association of Research Ethics Committees has not been well explored. In this article, a simple statistical approach for the study of the confidence in a model is proposed. The approach can pave the way to a potentially useful method to estimate a sensible number of subjects which is in accordance with the general principles of ethical bodies from all over the world.
Keywords: Research ethics; Experimental design; Leverage; Number of subjects
Uncertainty of atomic absorption spectrometer by Yoshihiro Hirano; Kyoko Imai; Kazuo Yasuda (pp. 190-196).
The uncertainty of the flame atomic absorption spectrometer was studied. Drift of signal, noise, and nonlinearity of the calibration curve were found to be main sources of uncertainty for the absorbance measurement, and factors affecting these sources of uncertainty were evaluated using Cd as a typical element. The combined uncertainty was 0.00133 absorbance units at a Cd concentration of 0.5 mg/l (0.078 absorbance units). The relationship between the flame conditions and the burner optics contributed strongly to the uncertainty. Therefore, the matrix effect of the sample must to be taken into consideration in actual analyses.
Keywords: Atomic absorption spectrometer; Flame; Uncertainty of instrument
Uncertainty in photometric analysis: a case study by Julia Traks; Lilli Sooväli; Ivo Leito (pp. 197-207).
A procedure for estimation of measurement uncertainty of photometric analysis based on the ISO GUM method is presented. Two variations of the procedure—for the calibration graph and the standard addition method, respectively—are discussed. The variations are based on mathematical models involving 64 and 80 input quantities, respectively. The uncertainty of the result strongly depends on changes in experimental details. These dependencies are explored for a practical example of determination of the iron content of aluminum. The importance of taking uncertainty from sample preparation into account in uncertainty estimation is stressed. The number of effective degrees of freedom is calculated and discussed. The examples are available as GUM Workbench files in the Electronic Supplementary Material.
Keywords: Measurement uncertainty; ISO GUM; Photometry; Metrology in chemistry
Reflections regarding uncertainty of measurement, on the results of a Nordic fatigue test interlaboratory comparison by Magnus Holmgren; Thomas Svensson; Erland Johnson; Klas Johansson (pp. 208-213).
This paper presents the experiences of calculation and reporting uncertainty of measurement in fatigue testing. Six Nordic laboratories performed fatigue tests on steel specimens. The laboratories also reported their results concerning uncertainty of measurement and how they calculated it. The results show large differences in the way the uncertainties of measurement were calculated and reported. No laboratory included the most significant uncertainty source, bending stress (due to misalignment of the testing machine, “incorrect” specimens and/or incorrectly mounted specimens), when calculating the uncertainty of measurement. Several laboratories did not calculate the uncertainty of measurement in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) [1].
Keywords: Uncertainty of measurement; Calculation; Report; Fatigue test; Laboratory intercomparison
Uncertainty in chemical analysis for the example of determination of caffeine in coffee by M. Kolb; S. Hippich (pp. 214-218).
The comprehensive quantifying of uncertainty for the determination of caffeine in coffee is given according to the EURACHEM/CITAC Guide. The cause–effect diagram is very useful for the identification of the sources of uncertainty and the relationship between them. In this case the uncertainty caused by the pipette, the stock solution and the calibration curve are the three main sources. Concerning the concentration of the stock solution the purity of the caffeine was most important. The combined uncertainty showed that none of the three parts (stock solution, pipette, calibration curve) can be neglected. The expanded uncertainty (coverage factor k=2) is about 5.4%.
Keywords: Uncertainty; Quality assurance; Caffeine; High-performance liquid chromatography
Performance testing activities for analytical assessment of supercritical fluid extractors by B. Palenzuela; L. Manganiello; R. Bauza; A. Ríos; M. Valcárcel (pp. 219-228).
Systematic performance testing activities for supercritical fluid extractors consistent with the implementation of quality systems in analytical laboratories are proposed. In this context, supercritical fluid extraction (SFE) is used for the automatic processing of complex samples. Ensuring reproducible operation of SFE equipment is crucial with a view to obtaining traceable results. To this end, an assessment protocol including recommended preventive and corrective actions, and complementary internal quality control activities, was developed with a view to facilitating the use of SFE equipment by routine analytical laboratories.
Keywords: Supercritical fluid extraction; Performance testing; Quality control; Quality assessment
Quality criteria of the isotope dilution method for the determination of polycyclic aromatic hydrocarbons, petroleum-derived hydrocarbons and phenol in leachate of large-scale lysimeter experiments by Karl-Werner Schramm; Bernhard Henkelmann; Daniela Peschke; Dieter Martens (pp. 229-234).
A comprehensive analytical procedure for polycyclic aromatic hydrocarbons, petroleum-derived hydrocarbons and phenol using the isotope dilution method and employing high-resolution gas chromatography and mass spectrometry was developed and validated for leachates from source-term experiments and the different sampling sites of lysimeters. The use of glassware and other materials is efficiently limited to minimize the risk of contamination. The relative standard deviation elaborated allows precise reliable measurements. Limit of detection and recovery data are useful to judge the quality of each single measurement.
Keywords: Polycyclic aromatic hydrocarbons; Phenol; Petroleum-derived hydrocarbons; High-resolution gas chromatography–mass spectrometry; Leachate; Lysimeter; Validation
Measurement uncertainty of iodine determination in radiochemical neutron activation analysis by Andrej Osterc; Vekoslava Stibilj (pp. 235-240).
The measurement uncertainty of iodine determination in NIST standard reference material (SRM) 1549 using radiochemical neutron activation analysis (RNAA) was studied. This method is based on ignition of the irradiated sample [127I(n,γ)128I, t1/2=25 min, Eγ=422.9 keV] in an oxygen atmosphere, followed by absorption of iodine in a reducing acid solution and its purification by a selective extraction–stripping–reextraction cycle. The purified solution of iodine in CHCl3 was transferred to a well-type HPGe detector for γ-ray measurement of the induced radionuclide 128I. The detection limit of the method employed under the conditions described was 1 ng/g. The reproducibility of iodine determination in the SRM was 3.6% (12 determinations within 1 month), calculated by the analysis of variance procedure. Using the commercially available software program GUM Workbench and the recommendations of the Eurachem/CITAC Guide, we evaluated the uncertainty budget for this RNAA method and the relative uncertainty obtained was 3.6%. The largest uncertainty contributions were due to the repeatability of the chemical yield determination, the count rate of the induced nuclide in the standard and sample, the mass of the carrier and the mass of the irradiation standard.
Keywords: Iodine; Measurement uncertainty; Radiochemical neutron activation analysis
Determination of PCBs in river sediment samples—proficiency test for selected Polish laboratories by Piotr Konieczka; Thomas P. J. Linsinger; Bogdan Zygmunt; Jacek Namieśnik (pp. 241-251).
Eighteen Polish laboratories participated in a proficiency test for the determination of PCBs in river sediment. The participants used their in-house method. The aim of the exercise was to obtain information about the “state of the art” of PCB analysis in environmental samples. Five PCBs (IUPAC nos. 52, 118, 138, 153 and 180) were selected for the test. The relative standard deviation of the analytical results submitted varied from 45 to 65%, with an outlier rate of 7%. The averages of the results for all analytes were in good agreement with reference values.
Keywords: Proficiency test; Polychlorinated biphenyls; River sediment; Gas chromatography
Sampling and uncertainty — Reply to the letters [1,2] to the editor
by Samuel Wunderli (pp. 255-256).
What is relevant in clinical laboratory sciences, goals or requirements?
by Xavier Fuentes-Arderiu (pp. 257-258).
Which changes will be brought about by the new edition of ISO/IEC 17025?
by Monika Wloka (pp. 259-260).
Summary from the workshop “Building an Appropriate Metrology Infrastructure in South Eastern European Countries”
by Nineta Majcen; Piotr Robouch; Ani Todorova; Philip Taylor (pp. 261-263).