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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.11, #3)
Must participation in an interlaboratory comparison be (very) frequent?
by P. De Bièvre (pp. 105-106).
Simultaneous confidence and prediction bands in the certification of pressure-volume curves for the pore size analysis of solids by means of mercury porosimetry by Barbara Röhl-Kuhn; Jörg Polzehl; Peter Klobes (pp. 107-115).
The pore size analysis of solids is widely applied in chemical industries, materials engineering, ceramic production, environmental engineering, catalysis, chromatography, nanotechnology, and many other fields. In spite of several new methods used for determining the pore size distribution of meso- and macropores [see IUPAC Recommendations of 1994], mercury porosimetry has remained one of the most popular methods employed for the characterisation of porous materials. In this paper, a new way is described for the estimation of certified pressure-volume curves from experimental curves measured by different laboratories in connection with the certification of new reference materials for a comparatively low-pressure range of mercury intrusion (<2 MPa). Simultaneous confidence and prediction bands for the certified pressure-volume curves are constructed by bootstrapping.
Keywords: Mercury intrusion; Certified reference material; Certified pressure-volume curve; Bootstrap confidence bands; Bootstrap prediction bands
Feasibility study for the preparation of certified reference materials part I – mineral oil contaminated soils by Pirjo Sainio; Irma Mäkinen; Jaap-Willem Hutter; Theo den Ouden; Mikael Krysell (pp. 116-121).
The international joint project HYCREF (Contract No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogeneous and stable reference materials of water, soil, and waste contaminated with mineral oil hydrocarbons and to certify the mineral oil content by gas chromatographic methods. The results of a feasibility study for the preparation of three soil reference materials are discussed in this paper, and for the preparation of three waste reference materials in the second part (Koch et al., Accred Qual Assur submitted for publication). The soil materials were selected to represent different soil types and contamination levels. The project plan set three requirements for these reference materials: uncertainty in the mineral oil content resulting from the certification exercise <5%, a sample inhomogeneity of <3% and a minimum long-term stability of 5 years. For the most part, these requirements were met within this project.
Keywords: Mineral oil hydrocarbons; Soil; Gas chromatography; Certified reference materials
Feasibility studies for the preparation and certification of reference materials Part II: mineral oil contaminated waste materials by Matthias Koch; Almuth Liebich; Tin Win; Irene Nehls; Arne Lund Kvernheim; Oddvar Ringstad; Frøydis Oreld (pp. 122-129).
The 2-year international joint project HYCREF (Contract-No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogenous and stable water-, soil- and waste reference materials contaminated with mineral oil hydrocarbons and to test certify the mineral oil content by gas chromatographic methods. As mineral oil products are important sources for environmental contaminations, appropriate reference materials certified by using the new gas chromatographic methods (soil: ISO/FDIS 16703, waste: prEN 14039 and KW/04, water: ISO 9377-2) are highly needed. Additional to the HYCREF-results presented in part I–mineral contaminated soils–this second paper gives an overview of the feasibility study for the preparation and test certification of three waste reference materials (offshore marine sediment, building material and industrial waste). The following specifications, which had been defined in the project work plan, were reached successfully: uncertainty of the mineral oil content resulting from the certification exercise ≤5% and a between-bottle inhomogeneity of ≤3%. All three materials have been evaluated for long- and short term stability. They contain different levels and types of mineral oil and cover the full application range of ISO/FDIS 16703 and prEN 14039 (100–10,000 mg/kg). The expanded uncertainties U cert of the three materials are about 6%. In this way, they are comparable to ERM®-CC015a (U cert=7.1%, mineral oil in a river sediment) and are suited to close the present gap of commercially available CRM for mineral oil determination in waste.
Keywords: Mineral oil hydrocarbons; Feasibility study; Certified reference materials (CRM); Waste materials; Gas chromatography
Estimation of uncertainty in the determination of nitrogen oxides emissions by Joao F. P. Gomes; Vitor M. A. Cruz; Maria L. C. Ribeiro (pp. 138-145).
This paper presents a methodology for estimation of uncertainty on a reference test method for the determination of nitrogen oxides concentration in gaseous emissions from stationary sources. As a first stage for identification of uncertainty sources, the test method is carefully reviewed in detail. Afterwards, these sources are quantified, bearing in mind its partial uncertainty, allowing the determination of the combined uncertainty and, finally, the expanded uncertainty. The calculation procedure was implemented into an excel calculation file. Using this file and considering several numerical applications from real situations, uncertainities around 15 mg/Nm3 over determined concentrations of 350 mg/Nm3 of NO x (expressed as NO2) were obtained.
Keywords: Uncertainty; Gaseous effluents; Nitrogen oxides
In defence of the correlation coefficient by Stephen L. R. Ellison (pp. 146-152).
The relationship between calibrated range, residual standard deviation and correlation coefficient r is discussed. It is shown that in typical chemical calibration applications with appropriately distributed calibration points (particularly, with range comparable to mean and with approximately even or with ‘successive dilution’ spacing), the linear correlation coefficient has valid application as a routine criterion for acceptable fit if used with due care.
Keywords: Correlation coefficient; Linearity