The interlaboratory comparison "IMEP-19 trace elements in rice"—a new approach for measurement performance evaluation

The aim of IMEP is to present objectively the quality of chemical measurements. Participants in IMEP compare their reported measurement results with independent external certified reference values with demonstrated traceability and uncertainty, as evaluated according to international guidelines. IMEP-19 focused on measurements of trace elements in rice aiming to support the Commission Regulation (EC) No. 466/2001 on maximum levels for certain contaminants in foodstuff. Measurement results for the elements Cd, Cu, Pb and Zn were reported by 267 field laboratories involved in food analysis from 43 countries. Performance criteria for the evaluation of the reported measurement results in IMEP-19 are suggested. The chosen performance indicators not only take into account the deviation of the reported measurement value from the certified reference value, but also set criteria for maximum and minimum acceptable uncertainty. The IMEP-19 participants' performance is reviewed by means of using new simple graphical tools, called "Naji plots".     

Interference of ascorbic acid in the sensitive detection of dopamine by a nonoxidative sensing approach

The electrochemistry of a poly(anilineboronic acid)/carbon nanotube composite was studied in the presence of dopamine and ascorbic acid. To understand the binding affinity of dopamine and ascorbic acid to the boronic acid functional groups in the composite, the association constants between the diol groups in dopamine and ascorbic acid and the boronic acid were experimentally determined using a fluorescence-based binding assay. The results demonstrate that ascorbic acid could severely interfere with the detection of dopamine in nonoxidative boronic acid-binding approaches: Ascorbic acid was able to electrocatalytically reduce the fully oxidized polyaniline backbone during the electrochemical oxidation process; similarly to dopamine, ascorbic acid was also able to bind to the boronic acid groups through its planar diol group even though the binding affinity is much lower. The examination of the dopamine transduction mechanism and ascorbic acid interference mechanism in this nonoxidative approach will benefit the design of future boronic acid-based sensors.     

The use of multiple correspondence analysis for the evaluation of inter-laboratory comparisons

Participation in inter-laboratory comparisons (ILC) is one of the recommended means of external quality control according to ISO/IEC 17025:2005. Providers of ILC or proficiency test (PT) schemes collect, besides the measurement results on the test samples, information on the sample treatment and measurement procedure. The objective of this paper is to evaluate in a non-traditional way, using numerical and non-numerical data provided by the participants in IMEP-20 (trace elements in tuna fish), the additional information concerning the applied analytical methods and the accreditation/nomination status. Arsenic was taken as an example. The basic statistical procedure for the evaluation of questionnaire information was the multiple correspondence analysis (MCA). Univariate clustering techniques were applied for the categorization of the numerical data (measurement values). The methodology of the evaluation of supplementary non-numeric information used in this paper might serve (a) to providers of ILC (PT) schemes to modify/improve their questionnaires and (b) to give laboratories better guidance in the methods used for the determination of various analytes in different matrices. This paper is meant serve as a guide for the possible interpretation of the questionnaires accompanying ILC schemas. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel     

Kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD)

The kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD), an arenediazonium ion newly developed as a derivatizing reagent for drug analysis, are described. The arenediazonium ion, in an optimized concentrated sulfuric acid/orthophosphoric acid medium, was incubated for various time intervals at 30 degrees, 45 degrees, 55 degrees , 65 degrees , 75 degrees, and 85 degrees C. The amount of ion left after each time interval was quantified selectively by colorimetric assay at 490 nm, using mefenamic acid as a model diazo-coupling component. The rate constants for the decomposition were determined graphically. An Arrhenius plot was used to delineate the dependence of the rate constant on temperature and to predict the half-life at 25 degrees C and lower temperatures. The diazonium ion decomposed by first-order kinetics. The rate constants of decomposition, which increased progressively with temperature, were 3.18 +/- 0.41 x 10(-5), 1.19 +/- 0.07 x 10(-4), 4.87 +/- 0.15 x 10(-4), 12.88 +/- 0.73 x 10(-4), and 21.32 +/- 2.74 x 10(-4) (s(-1)) with corresponding half-lives of 363, 97.06, 23.72, 8.97, and 5.42 min at 30 degrees, 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, respectively. CDNBD is highly stable in concentrated acid medium, with half-life values of about 10 h, 10 days, and 7.3 months at 25 degrees, 0 degrees, and -20 degrees C, respectively. The reagent stability profile shows that it could be readily adapted for routine applications in instrumental chemical analysis.     

Contribution of an interlaboratory comparison to the certification of the STAM/IRMM-0243 243Am reference material

Following the expression of the need for an americium (Am) standard and particularly for one with a certified americium-243 (²⁴³Am) content, the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA)/Direction de l’Energie Nucléaire of Marcoule and the European Commission Joint Research Center in Geel carried out a collaborative project for the production of a certified reference material enriched in ²⁴³Am. CEA’s Commission d’ETAblissement des Méthodes d’Analyse organized an interlaboratory comparison on this material prior to the issuing of its certificate. The usefulness of an interlaboratory comparison to assess the measurement capabilities in the field and to confirm the provisional certified values for the amount contents of ²⁴³Am, ²⁴¹Am, total Am, the isotopic composition and the molar mass of Am has been demonstrated. Furthermore this interlaboratory comparison enabled to derive an indicative value for the n(^242mAm)/n(²⁴³Am) isotope amount ratio.

     

Stability monitoring of selected spike isotopic reference materials for isotope dilution mass spectrometry

Journal of Radioanalytical and Nuclear Chemistry - The provision of high quality spike isotopic reference materials is one of the objectives of the Joint Research Centre of the European Commission....     

Evaluation of laboratory performance in IMEP water interlaboratory comparisons

The aim of International Evaluation Programme (IMEP) is to present objectively the quality of chemical measurements. Participants in IMEP compare their reported measurement results with independent external certified reference values with demonstrated traceability and uncertainty, as evaluated according to international guidelines. Three major interlaboratory comparisons (ILCs), IMEP-6, IMEP-9 and IMEP-12, on trace elements in water were carried out from 1994 to 2000. Participants' results for Cd, Fe and Pb concentrations from these three different IMEP water ILCs were compared by means of suitable performance indicators. The performance evaluation criteria were set according to the requirements stated in the Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption. Two different performance indicators were selected for evaluation of the individual participants' results: the commonly used z-score and the not so well-known E _n number. The group performance indicator is based on the variation of z-scores. To assess the individual measurement performance, not only the deviation of the reported measurement values from the certified reference value, but also criteria for maximum and minimum acceptable uncertainties were taken into account. The participants' performance is also reviewed by means of using a simple graphical tool, called “Naji-plots”.     

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.’