A practical procedure for assigning a reference value and uncertainty in the frame of an interlaboratory comparison

A method is suggested for the calculation of a reference value and its uncertainty to be used in the frame of an interlaboratory comparison (ILC). It is assumed that the reference value of the measurand is determined independently from the ILC round. It is derived from a limited set of measurement results obtained from one or several expert laboratories. The procedure involves three stages: (1) check of the experimental data and possible corrections; (2) check of the consistency of data, and possibly increase of the uncertainties in order to attain internal consistency; (3) choice between fully, partially or un-weighted mean.     

Bioaccumulation of uranium 234U and 238U in marine birds

In the paper was presented results of our study about uranium ²³⁴U and ²³⁸U radioactivity in the marine birds samples, collected in the Polish area of the southern Baltic Sea. We chose 11 species of sea birds: three species permanently residing at southern Baltic, four species of wintering birds and three species of migrating birds. The obtained results indicated that uranium is very irregularly distributed in organs and tissues of marine birds. The highest uranium content is characterized in liver, rest of viscera and feathers, the smallest in skin and muscles. The uranium concentration was higher for carnivorous species (long-tailed duck (C. hyemalis), common eider (S. mollissima), lower for species eating fish (great cormorant (P. carbo), common guillemot (U. aalge), red-throated diver (G. stellata) and razorbill (A. tarda)), but the biggest amounts for herbivorous species [tufted duck (A. fuligula) and eurasian coot (F. atra)]. About 63–67% of uranium, which was located in feathers of two species of marine birds: razorbill (A. tarda) and long-tailed duck (C. hymealis), was apparently adsorbed, which suggests that uranium adsorption on the feathers may be an important transfer from air to water.     

The precise determination of 239Np for the evaluation of 238U capture cross-sections at varying neutron energies in a zero-energy fast reactor

A method is described for the determination of ²³⁹Np in natural uranium metal foils irradiated in a zero-energy reactor. The foils are dissolved in nitric acid in the presence of ²³⁷Np used for the determination of the yield of ²³⁹Np. Neptunium is co-precipitated with lanthanum fluoride; lanthanum and thorium are removed by anion exchange in hydrochloric acid solution, and the neptunium is further purified by anion exchange in nitric acid solution. Sources for counting are prepared by direct evaporation of an aqueous solution onto a stainless steel disc. No corrections are necessary to the ²³⁷Np α-count for absorption in the source. The method does not necessitate prior separation of daughter ²³³Pa from the ²³⁷Np tracer and gives sources of high purity in good yield.     

First results studying the transmutation of 129I, 237Np, 238Pu, and 239Pu in the irradiation of an extended natU/Pb-assembly with 2.52 GeV deuterons

An extended U/Pb-assembly was irradiated with an extracted beam of 2.52 GeV deuterons from the Nuclotron accelerator of the Laboratory of High Energies within the JINR in Dubna, Russia. The lay-out of this experiment and first results are reported. The Pb-target (diameter 8.4 cm, length 45.6 cm) is surrounded by a ^natU-blanket (206.4 kg) and used for transmutation studies of hermetically sealed radioactive samples of ¹²⁹I, ²³⁷Np, ²³⁸Pu and ²³⁹Pu. Estimates of transmutation rates were obtained as result of measurements of gamma-activities of the samples. Information about the spatial and energy distribution of neutrons in the volume of the lead target and the uranium blanket was obtained with sets of activation threshold detectors (Al, Y and Au) and solid state nuclear track detectors (SSNTD). An electronic ³He neutron detector was tested on-line. A comparison of experimental data with theoretical model calculations using the MCNPX program was performed yielding satisfactory results. Collaboration “Energy plus Transmutation” This work is dedicated to the cherished memory of Professor Vladimir Pavlovich Perelygin from the JINR in Dubna, Russia.     

Measurement of the radioactivity of 238U, 226Ra, 210Pb, 228Th, 232Th, 228Ra, 137Cs and 40K in tea using gamma-spectrometry

The aim of the present work was to determine the concentration of radionuclides in all kinds of tea available at the local Egyptian market. Radioactivity of the nuclides ²³⁸U, ²²⁶Ra, ²¹⁰Pb, ²²⁸Th, ²³²Th, ²²⁶Ra, ¹³⁷Cs and ⁴⁰K were measured in tea by direct γ-ray spectrometry using HPGe detector and their mean values were 16.0±5.3, 3.1±0.7, 34.3±3.4, 3.4±1.2, 3.0±0.6, 3.1±0.8, 0.9±0.2 and 623±25 Bq·kg⁻¹, respectively.     

Evaluation of the stability of ethanol in water certified reference material: measurement uncertainty under transport and storage conditions

This study simulated the transport and storage conditions of ethanol in water certified reference material (CRM) produced by the Chemical Metrology Division of Inmetro—DQUIM with the purpose of estimating the measurement uncertainty related to stability. The short-term stability study was performed on five different mass fractions (w) in terms of mg ethanol/g solution of the ethanol in water CRM. The nominal values are w = 0.5, 0.9, 1.1, 3.8 and 4.6 mg/g, at temperatures of 4 and 60 °C. On the other hand, the long-term stability study was developed on four different mass fractions (nominal values): w = 0.5, 0.9, 1.1 and 4.6 mg/g, at a temperature of 20 °C. This paper will show the data from the long-term stability study that took place over 52 weeks. The method used complies with ISO Guide 35, the BCR Guideline for Feasibility Studies and ISO Guide 34. According to the statistical parameters used in both studies, the stability of ethanol in water CRM was confirmed for all of the mass fractions studied.     

An interlaboratory study to improve the quality of chemical and biological measurements in waste water

 Analyses of waste water are routinely performed to monitor the level of contamination. To verify the quality of such determinations the National Institute of Chemistry, with the support of the Ministry of Environment and Spatial Planning and the Slovenian Accreditation Agency, organizes interlaboratory comparisons. Over the last 3 years, five interlaboratory trials named "MPP-Waste Water" were organized. Each round attracted around 50 participants, mostly from Slovenia and some from abroad, which enabled the testing of SIST ISO methods or alternative methods. We prepared samples for determination of harmful substances that are important for the characterization of waste water; physico-chemical parameters (pH), global parameters – chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), metals (mercury, cadmium, copper, nickel, lead and chromium (VI)), nutrients (ammonia and total phosphorus), anions (chloride, nitrite, nitrate, sulphate) and toxicity to Daphnia magna. For the analysis of each parameter we prepared two samples at two different concentration levels. The materials used in the proficiency testing were carefully prepared and their homogeneity and stability were verified. The purpose of this scheme was to enable participants to check their day-to-day analytical performance. The results should enable the participants to improve the quality of their analyses.

---

---

Received: 24 October 2002 Accepted: 2 January 2003

---

Acknowledgments We would like to thank the Ministry of Environment and Spatial Planning and the Ministry for Education, Science and Sport for providing financial support. We would like to thank members of the Technical Committee: Mrs. Marjana Kovacˇicˇ, Dr. Katja Otrin-Debevc, Prof. Dr. Marjan Veber and Mrs. Boža Gregorc for their valuable support. Special thanks are due to Dr. Adrian Van der Veen who helped us in running the first PT.

---

Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia

---

Correspondence to M. Cotman     

Determination of uranium in solution at the ng 1−1 level by time-resolved laser-induced spectrofluorimetry: application to geological samples

Time-resolved laser-induced spectrofluorimetry was used for the determination of uranium at the ng 1^?1 level in alkaline water with high chloride and sulphide contents in order to obtain a better understanding of uranium mobilization under natural reducing conditions. The optimum complexing medium, limit of detection and results obtained for several waters from different localities in the Pyrenees are presented. These data seem to confirm that even at very low uranium concentrations, thermodynamic control by a mineral phase takes place.     

Evaluation of measurements of 238Pu, 239Pu and 240Pu in urine at the microbecquerel level using thermal ionization mass spectrometry and alpha-spectrometry at Los Alamos National Laboratory: Results of a two year comparison test (LA-UR-06-8055)

The Intercomparison Studies Program (ISP) at the Oak Ridge National Laboratory (ORNL, Oak Ridge, TN, USA) provides natural-matrix urine quality-assurance/quality-control (QA/QC) samples to radiobioassay analysis laboratories. In 2003, a single laboratory (Los Alamos National Laboratory LANL, Los Alamos NM USA) requested a change in the test-samples provided previously by the ISP. The change was requested to evaluate measurement performance for analyses conducted using thermal-ionization mass spectrometry (TIMS). Radionuclides included ²³⁹Pu at two activity levels (75–150 μBq^·sample⁻¹ and 1200–1600 μBq^·sample⁻¹) and ²³⁸Pu (3700–7400 μBq^·sample⁻¹). In addition, ²⁴⁰Pu was added to the samples so that the ^239+240Pu specific activity was 3700–7400 μBq^·sample⁻¹. In this paper, the results of testing during the period May, 2003 through September, 2005 are presented and discussed.     

Significant improvements in the analysis of perfluorinated compounds in water and fish: Results from an interlaboratory method evaluation study

The 2nd international interlaboratory study (ILS) on perfluorinated compounds (PFCs) in environmental samples was organized to assess the performance of 21 North American and European laboratories on the analysis of PFCs in water and fish. A study protocol was provided to assess accuracy, precision, matrix effects and to study the use of in-house standards. The participants used shared native and mass-labelled standards that were provided for this study to quantify the PFC concentrations in the samples. Matrix effects in the determination of PFCs can be considerable and can decrease the sensitivity, the accuracy and internal standard recoveries. Therefore, two quantification methods were evaluated by all laboratories: standard addition quantification (SAQ) and solvent-based calibration curve quantification (SBCCQ; using mass-labelled internal standards (IS)). The between laboratory reproducibility (i.e. coefficient of variance) was smaller for the SBCCQ results (except for PFBS and PFHxS for which no mass-labelled analogues were available) compared to those obtained by the SAQ method. The within laboratory precision of individual laboratories is good (mean for all PFCs in water 12% and 6.8% in fish). The good performance is partially attributable to the use of well-defined native- and mass-labelled standards. Therefore, the SBCCQ method is recommended. The results show that analytical methods for PFCs in water and fish have improved considerably. Critical steps identified in this study are (i) the use of well-defined native standards for quantification, (ii) the use of mass-labelled internal standards (preferably one for each target compound) and (iii) minimization of matrix effects by a better clean up.     

Comparison of ISO-GUM and Monte Carlo methods for the evaluation of measurement uncertainty: application to direct cadmium measurement in water by GFAAS

The propagation stage of uncertainty evaluation, known as the propagation of distributions, is in most cases approached by the GUM (Guide to the Expression of Uncertainty in Measurement) uncertainty framework which is based on the law of propagation of uncertainty assigned to various input quantities and the characterization of the measurand (output quantity) by a Gaussian or a t-distribution. Recently, a Supplement to the ISO-GUM was prepared by the JCGM (Joint Committee for Guides in Metrology). This Guide gives guidance on propagating probability distributions assigned to various input quantities through a numerical simulation (Monte Carlo Method) and determining a probability distribution for the measurand.In the present work the two approaches were used to estimate the uncertainty of the direct determination of cadmium in water by graphite furnace atomic absorption spectrometry (GFAAS). The expanded uncertainty results (at 95% confidence levels) obtained with the GUM Uncertainty Framework and the Monte Carlo Method at the concentration level of 3.01 μg/L were ±0.20 μg/L and ±0.18 μg/L, respectively. Thus, the GUM Uncertainty Framework slightly overestimates the overall uncertainty by 10%. Even after taking into account additional sources of uncertainty that the GUM Uncertainty Framework considers as negligible, the Monte Carlo gives again the same uncertainty result (±0.18 μg/L). The main source of this difference is the approximation used by the GUM Uncertainty Framework in estimating the standard uncertainty of the calibration curve produced by least squares regression. Although the GUM Uncertainty Framework proves to be adequate in this particular case, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.     

IMEP-12: trace elements in water; objective evaluation of the performance of the laboratories when measuring quality parameters prescribed in the European Directive 98/83/EC

The International Measurement Evaluation Programme (IMEP) is an interlaboratory comparison scheme, founded, owned and co-ordinated by the Institute for Reference Materials and Measurements (IRMM) since 1988. IMEP-12, for the fourth time in the series, focused on trace elements in water and it was designed specifically to support European Commission directive 98/83/EC. Reference values for the concentration of ten elements were established with expanded uncertainties according to GUM. In total, 348 laboratories from 46 countries in five continents participated in the comparison and the degree of equivalence between the results of the laboratories and the reference values is presented graphically. Samples from the same batch were distributed to ten laboratories from European Countries, which represented their country in the framework of the EUROMET project 528. Participation in this comparison was offered to the European Co-operation for Accreditation (EA) for participation of accredited laboratories from all over Europe in the framework of the collaboration between IRMM and EA and to laboratories from the EU new member states and acceding countries in the frame of IRMM’s ‘Metrology in Chemistry support program for EU new member states and acceding countries.’     

Distortions in trihapto-allyls induced by electronic asymmetry: A comparison of the structures of (η5-C5H5)Mo(CO)2(η3-C3H5) and (η5-C5H5)Mo(NO(I)(η3-C3H5)

The electronic asymmetry induced by replacing two carbonyls by a nitrosyl and iodide ligand causes severe distortion in the allyl moiety. The allyl group in the nitrosyl complex is bound in a sigma-pi mode rather than the symmetrical mode found in the dicarbonyl. This change in ground state structure alters the exo—endo conformer interconversion mechanism from a rotation of the allyl in the dicarbonyl to a sigma-pi interconversion in the nitrosyl iodide.     

Use of 18O water and ESI-MS detection in subsite characterisation and investigation of the hydrolytic action of an endoglucanase

We present a novel method for investigating subsite-substrate interactions of glycoside hydrolases and the determination of the oligosaccharide cleavage point based on the analysis of the hydrolysis products produced in the presence of ¹⁸O-labelled water. Conventional techniques for such determination of the hydrolysis pattern call for the chemical modification of the substrate, whereas the method presented makes it possible to use natural substrates, utilising the selectivity and sensitivity of mass spectrometry. This method is very useful for the detection and analysis of enzyme-catalysed hydrolysis, provided that the conditions are chosen where ¹⁸O incorporation without the presence of the enzyme is absent or undetectable. Such conditions were found and used in incubations of cellopentaose with the well-characterised endoglucanase Cel5A from Bacillus agaradhaerens. We were able to confirm that the preferred glycoside bond to be hydrolysed is the third one counting from the non-reducing end of the cellopentaose. Thus, cellopentaose prefers to bind from the –3 to the +2 subsites, which is in accordance with published crystallographic data. The main advantage of the method presented is that there is no need for a priori chemical modification/labelling of oligosaccharide substrates, which are processes that can disturb the enzyme–substrate interaction. From ¹⁸O incorporation we could demonstrate that the enzyme also has an oxygen-exchange activity on cellotriose and cellobiose. This is in agreement with the mechanism for transglycosylation and indicates that it is possible for the enzyme to perform such reactions.     

Minor and trace element contents in pituitary gland of “normal” humans: an evaluation of analytical data

In the study of trace elements in the different human brain areas, a critical evaluation of the values available in the literature is of great importance in attempting to establish reliable baseline levels, i.e., Reference Values (RVs) for toxicological assessment studies.This paper reviews the published values of minor and trace elements in the pituitary gland (hypophysis) of “normal” humans.Eighteen published papers are taken into account, 15 of which refer to the entire gland, whereas in three of them, only the adenohypophysis is considered.It turns out that essential elements such as Cu, Fe, Se and Zn were more frequently determined, whereas As, Br, Ca, Co, Cr, Cs, K, Mg, Mn, Ni and Rb were seldom investigated.Mercury was determined by several authors because of the concern caused by Hg release from dental amalgam fillings.Most values were obtained by Neutron Activation Analysis (NAA), which appears to have played a pioneer role in this field.Literature data on trace element levels in pituitary gland are at present insufficient to establish RVs; rather, they can be considered only as indicative values.Future investigations based on large populations of control subjects, with standardization of the preanalytical factors and the use of fit-for-purpose Standard or Certified Reference Materials (SRMs, CRMs) should therefore be envisaged.     

Dispersive liquid–liquid microextraction based on solidification of floating organic droplet for the determination of triazine and triazoles in mineral water samples

A simple, rapid, and sensitive method for the determination of atrazine, simazine, cyproconazole, tebuconazole, and epoxiconazole in mineral water employing the dispersive liquid–liquid microextraction with solidification of a floating organic drop with determination by liquid chromatography tandem mass spectrometry has been developed. A mixed solution of 250 μL 1‐dodecanol and 1250 μL methanol was injected rapidly into 10 mL aqueous solution (pH 7.0) with 2% w/v NaCl. After centrifugation for 5 min at 2000 rpm, the organic solvent droplets floated on the surface of the aqueous solution and the floating solvent solidified. The method limits of detection were between 3.75 and 37.5 ng/L and limits of quantification were between 12.5 and 125 ng/L. The recoveries ranged from 70 to 118% for repeatability and between 76 and 95% for intermediate precision with a relative standard deviation from 2 to 18% for all compounds. Low matrix effect was observed. The proposed method can be successfully applied in routine analysis for determination of pesticide residues in mineral water samples, allowing for monitoring of triazine and triazoles at levels below the regulatory limits set by international and national legislations.     

Environmental isotopes (15N and 18O) in the assessment of groundwater degradation: Aveiro Quaternary aquifer (NW Portugal)

The Aveiro region, situated on the Northwest coast of Portugal is one of the most industrialized areas of Portugal. The shallow Quaternary aquifer system, mainly of detrital sediments of Pleistocene and Holocene ages, is still today an important water resource for this region despite growing evidence of diffuse pollution problems. Isotope techniques have been used to evaluate the aquifer vulnerability to nitrate contamination (δ¹⁸O and δ¹⁵N from NO₃ and δ²H and δ¹⁸O from H₂O). Nitrogen isotopes were used to identify nitrogen sources and assess agriculture, cattle-breeding, urban and industrial contributions to the nitrogen cycle in the Aveiro ecosystem.     

负载Fe2O3的Zr基钙钛矿催化剂对逆水煤气反应的影响

采用固相反应法制备了钙钛矿结构的BaZr_0.9Y_0.1O₃,并用BaZr_0.9Y_0.1O₃作为载体负载Fe₂O₃,通过X射线衍射分析（XRD）、扫描电子显微镜（SEM）观察负载型催化剂的晶相结构和微观形貌,同时考察了制备的催化剂的逆水煤气反应催化活性。结果表明,BaZr_0.9Y_0.1O₃粉体1200℃煅烧5h时,负载型催化剂具有较好的催化活性;BaZr_0.9Y_0.1O₃对逆水煤气反应有一定的催化作用,负载少量的Fe₂O₃催化剂可以明显促进CO₂还原,在空速为1.13h^-1,温度为650℃时,CO收率可以达到31%;催化剂经过长时间运行催化效果良好,制备的催化剂活性较稳定。