The consequences of the mutual recognition of measurement standards for international metrology

After stressing the importance in the modern world of accurate and reproducible measurements, the actions taken by the Bureau International des Poids et Mesures to set up, together with the regional metrology organizations, a series of key comparisons are described. They are the technical foundation of a mutual recognition of national measurement standards arrangement prepared in conjunction with the National Metrology Institutes (NMIs). This arrangement also includes the recognition of calibration and measurement certificates issued by these institutes. Then, the consequences of this arrangement for trade are described. The case of chemical analysis is illustrated by the application of the Kyoto protocol on the reduction of greenhouse gases. But the global workload to be taken up by the International Committee of Weights and Measures, its Consultative Committee for Amount of Substance and the NMIs is huge.     

The consequences of the mutual recognition of measurement standards for international metrology

 After stressing the importance in the modern world of accurate and reproducible measurements, the actions taken by the Bureau International des Poids et Mesures to set up, together with the regional metrology organizations, a series of key comparisons are described. They are the technical foundation of a mutual recognition of national measurement standards arrangement prepared in conjunction with the National Metrology Institutes (NMIs). This arrangement also includes the recognition of calibration and measurement certificates issued by these institutes. Then, the consequences of this arrangement for trade are described. The case of chemical analysis is illustrated by the application of the Kyoto protocol on the reduction of greenhouse gases. But the global workload to be taken up by the International Committee of Weights and Measures, its Consultative Committee for Amount of Substance and the NMIs is huge.

     

Metrology in chemistry – a public task

 The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods, and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration certificates (CIPM MRA) issued by the NMIs. Received: 19 April 2000 / Accepted: 28 July 2000     

CCQM primary methods symposium: how far does the light shine?

The Consultative Committee for Amount of Substance (CCQM) has the task of organizing a comprehensive set of international comparisons to establish the technical basis for the mutual recognition of measurement capabilities among the national measurement institutes (NMIs) in the field of chemical measurement. The challenge that the CCQM faces is to identify, design, and conduct a limited number of key comparisons to enable the assessment of measurement comparability among NMIs across the entirety of ’chemical measurement space’. This is no easy task because the field of chemical metrology is extremely diverse and multidimensional, owing to the number of measurand types, concentrations, and matrix types of importance. The ”CCQM primary methods symposium: how far does the light shine?” was organized to provide information and initiate discussions to assist in this challenge, and clarify how the concept of a primary method of measurement could be instrumental in achieving this goal.     

An international assessment of the metrological equivalence of higher-order measurement services for creatinine in serum

The Consultative committee for amount of substance-metrology in chemistry (CCQM)-K80 Key Comparison directly assessed the equivalence of many of the world’s higher-order value-assigned materials (HOVAMs) for creatinine in human serum. This 2009 international study compared the certified values and uncertainties of the materials using measurements made under repeatability conditions. The study evaluated 17 materials submitted by 6 national metrology institutes (NMIs). The creatinine quantity in these materials ranged from 3 mg/kg to 57 mg/kg (about 0.3 mg/dL to 6 mg/dL or 30 nmol/L to 500 nmol/L). All materials were stored and prepared according the specifications provided by the participating NMIs. Samples were processed and analyzed under repeatability conditions by one analyst using isotope-dilution liquid chromatography–mass spectrometry in two measurement campaigns. The certified values and repeatability measurements were compared using uncertainty-weighted generalized distance regression. The instrumental repeatability relative standard deviation was 1.2%. The measurement design required assessment of within-unit and between-campaign variability in addition to measurement repeatability. At a 95% level of confidence, the certified values for all 17 materials agreed to within their assigned uncertainties. CCQM-K80 demonstrated the metrological equivalence of the currently available HOVAMs for creatinine in human serum and of the creatinine measurement services provided by the participating NMIs.     

Electrical conductivity of solutions of the LiIO3-HIO3-H2O system

The electrical conductivity of aqueous LiIO₃ solutions and solutions of the LiIO₃-HIO₃-H₂O system is measured over a wide range of compositions at 25, 50, and 75°C. Isothermal surfaces of electrical conductivity are mapped, and the activation energies of conductivity are calculated. The conductivity isotherms in the LiIO₃-H₂O and HIO₃-H₂O boundary binary systems and in mixed solutions along sections with fixed electrolyte ratios each have a maximum as a function of electrolyte concentration. It is assumed that structure reorganization occurs in solutions in the concentration range corresponding to the peak conductivity. Proton migration features in the solutions in question are considered.     

Optimising calibration and measurement capabilities in terms of economics in conformity assessment

Calibration measurement capabilities (CMC) are key factors in declaring the metrological performance of national metrology institutes (NMIs). Different countries have different CMC capabilities, reflecting both the existing measurement science competence as well as the perceived national needs for traceable calibration. This paper deals with increasing interest in decision-making in conformity assessment in terms of effective costs associated with measurement, testing and incorrect decision-making. The work examines the CMCs of calibration laboratories and NMIs with economic decision theory, in particular, in terms of customer satisfaction and with respect to conformity assessment issues. Optimal strategies for calibration costs, maintenance of national measurement standards, testing and production costs are illustrated in practical examples. CMCs are an essential instrument to enable conformity assessment both for product safety, legal metrology, quality requirements as well as scientific research. The newly defined term “target measurement uncertainty”, introduced in the latest international metrology vocabulary (VIM), should be therefore always related to appropriate CMCs and related dissemination paths in the whole conformity assessment procedure. These requirements are clear and transparent justification for the development of required national metrological infrastructures, in order to fulfil the requirements of target measurement uncertainty for intended use or application in the particular conformity assessment procedure.     

Electrical conductivity of aqueous acids in binary and ternary water-electrolyte systems

We analyze electrical conductivity data for aqueous solutions of strong and weak acids over a wide range of concentrations at various temperatures. Electrical conductivity isotherms in these solutions are characterized by peaks, whose parameters correlate with the molecular structure of solutions. On the basis of the concentration dependence of the activation energy of electrical conductivity, the acid solutions are divided into two groups. One includes HIO₃, H₂SO₄, and H₃PO₄; the other includes HCl, HBr, HI, HClO₄, HNO₃, and carboxylic acids. We show that anomalous proton migration is operative only in low-concentration solutions until their concentration reaches the peak on conductivity isotherms. The effect of extrinsic ions on proton mobility and on conductivity in acid-salt-water systems is considered.     

Analysis of a copper alloy: Comité Consultatif pour la Quantite de Matière (CCQM) pilot study P76 international intercomparison

The capabilities of National Metrology Institutes (NMIs) and selected outside “expert” laboratories of determining the mass fractions of the main and minor elements Cu, Pb, Sn, Fe, and Ni in a lead-containing brass were assessed. This pilot study P76 was organized as an activity of the Inorganic Analysis Working Group of CCQM and was piloted by the Federal Institute for Materials Research and Testing (BAM). In total 12 laboratories (four NMIs and eight outside labs) submitted results, some of them more than one set of results per element. The laboratories were free to choose any analytical method they wanted to use for the analysis. Consequently various methods of measurement were employed: inductively coupled plasma optical emission spectrometry (ICP–OES), inductively coupled plasma mass spectrometry (ICP–MS), instrumental neutron-activation analysis (INAA), titrimetry, flame atomic-absorption spectrometry (FAAS), spectrophotometry (MAS), electrogravimetry, and gravimetric analysis. After testing for homogeneity within BAM, a certified reference material of lead-containing brass was used as test sample without informing the participants about the source of the material. The agreement of the results for all elements investigated was acceptable and mean values calculated from the results of all participants were close to the certified mass fractions of the CRM used as test sample. No statistically significant differences between the results of the NMIs and those of the non-NMIs could be observed.     

Semi-ideal solution theory. 2. Extension to conductivity of mixed electrolyte solutions

Conductivities were measured for the ternary systems NaCl-LaCl(3)-H(2)O and KCl-CdCl(2)-H(2)O and their binary subsystems NaCl-H(2)O, KCl-H(2)O, CdCl(2)-H(2)O, and LaCl(3)-H(2)O at 298.15 K. The semi-ideal solution theory for thermodynamic properties of aqueous solutions of electrolyte mixtures was used together with the Eyring absolute rate theory to study conductivity of mixed electrolyte solutions. A novel simple equation for prediction of the conductivity of mixed electrolyte solutions in terms of the data of their binary solutions was established. The measured conductivities and those reported in literature were used to test the newly established equation and the generalized Young's rule for conductivity of mixed electrolyte solutions. The comparison results show that the deviation of a ternary solution from the new conductivity equation is closely related to its isopiestic behavior and that the deviations are often within experimental uncertainty if the examined system obeys the linear isopiestic relation. While larger deviations are found in the system with large ion pairing effect, the predictions can be considerably improved by using the parameters calculated from its isopiestic results. These results imply that the previous formulation of the thermodynamic properties of aqueous solutions of electrolyte mixtures has a counterpart for transport properties.     

Aqueous solutions of lithium hydroxide at various temperatures: Conductivity and activity coefficients

The conductivity of LiOH aqueous solutions has been determined at 15, 25, and 45°C. The data analysis showed that LiOH is a slightly associated electrolyte, its association increasing with temperature. The association constant and distance parameter obtained from the conductivity data were successfully employed to calculate the activity coefficients of the solutions. The same procedure applied to very precise conductivity data for NaOH aqueous solutions enabled us to assess the reliability of this method of calculation of activity coefficients up to 0.1m. The alkali metal hydroxides show a reverse trend in the way their properties change with cationic radius, as is the case for the fluorides with which they are compared.     

Ionic Conduction in Electrolyte Solution

The electrical conductivity in aqueous solutions of electrolytes has been obtained in terms of inter-particle potentials and pair distribution functions, based on a generalized Langevin equation for the cation and anion. This treatment allows us to connect and compare with the work of a computer simulation where the inter-particle potentials are the only input. The results for the concentration dependence of electrical conductivity are basically represented as a function of the square root of concentration. The electrophoretic and relaxation effects are discussed from a microscopic view point. The ionic hydration in electrolytic solution is also discussed. Available inter-particle potentials in aqueous solutions of electrolytes are proposed. The numerical application is carried out for sodium chloride and other aqueous electrolyte solutions.     

Regularity of conductivity of concentrated aqueous solutions of strong electrolytes

Conductivity of concentrated aqueous solutions of strong electrolytes is analyzed in a wide range of temperatures and concentrations. The highest conductivity of solutions at a given temperature and the concentration corresponding to the highest conductivity are used as the generalizing parameters. It is shown that in the temperature range from 0 to 100°C and the concentration range from 0.1 to 12 M, the values of reduced conductivity (the ratio between the conductivity and its maximum value at a given temperature) for KOH aqueous solution fall on a common curve, if the reduced concentration (the ratio between the concentration of solution and the concentration corresponding to the highest conductivity) is used as the argument. The reduced conductivities of strong acids, bases, and salts of some I-I, I-II, II-I, III-I, and II-II electrolytes fall on the same curve.     

On the specific experience of national metrology institutes (NMIs) with national accreditation bodies (NABs)

The following paper addresses the experience of certain national metrology institutes (NMIs) with national accreditation bodies (NABs), in particular in small countries with emerging economies in new EU or candidate member states. Specific cases have been analysed primarily in some Central and South-East European countries. NABs under consideration are, in principle, members of European Co-operation for Accreditation (EA). EA cross-frontier policy in these cases will be discussed and resulting dilemmas outlined. Focus will be given to the problems of NMIs also performing calibrations, commercial calibration laboratories, and their relations with NABs. Due to numerous problems of smaller NABs, cross-frontier policy should stimulate cooperation between foreign and local accreditation bodies not only at the request of the calibration laboratory or some other conformity assessment body, but at the request of the local accreditation body in order to provide the best service for their local economy. As a solution to the accreditation problems, this paper proposes a process of gradual formation of a common European pool of experts, real-life common practices and, finally, maybe even some form of joint European accreditation service. The opinions expressed in the paper are personal statements of the author, and do not necessarily reflect the official opinions of the institutions of the author. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

A high-accuracy method of analysis of 19-norandrosterone in human urine as utilised for the international laboratory intercomparison CCQM-P68

A high-accuracy exact-matching isotope dilution mass spectrometry (IDMS) method for 19-norandrosterone (19-NA) in human urine was developed at NMIA for the certification of a freeze-dried human urine reference material (CRM NMIA MX002). The method utilised GC/HRMS analysis following hydrolysis, solvent extraction, HPLC fractionation and derivatisation. The method development included investigation of all potential analytical biases for the different stages of the method and included development of a confirmatory LC/MS/MS method. The measurement uncertainty of the reference method was rigorously investigated with the achieved expanded uncertainty being less than 4% at the 95% level of confidence. The method was used in the Comité Consultatif pour la Quantité de Matière (CCQM) pilot study CCQM-P68 which was an interlaboratory intercomparison for the analysis of 19-NA in human urine in which four national metrology institutes (NMIs) participated in. The agreement in the results from the NMIA method with those from the other NMIs was excellent.     

Purity determination as needed for the realisation of primary standards for elemental determination: status of international comparability

Within the National Metrology Institutes (NMIs) and designated laboratories, an interlaboratory comparison, CCQM-P107, was conducted to verify the degree of international comparability concerning the results of purity analysis. The mass fractions of Ag, Bi, Cd, Cr, Ni, Tl at the lower mg/kg-level in a high purity zinc material were determined, but the real measurand in metrological sense was the sum of the six mass fractions. Homogeneity was investigated by glow discharge mass spectrometry, reference values were obtained using isotope dilution mass spectrometry. Six NMIs participated, contributing eight independent data sets. The agreement amongst the results of the participants, their median and the agreement with the reference values were usually excellent and in almost all cases below the target uncertainty of 30% relative. In this manner, the accuracy of results and the comparability between the participants was demonstrated to be established.     

Computer-controlled measurement of thermal conductivities of aqueous salt solutions

A computer-controlled method to measure liquid thermal conductivities is described, and data are presented for aqueous electrolyte solutions. The relative thermal conductivities of sodium chloride and sodium iodide solutions agree well with previously published results. The effect of temperature on the thermal conductivity was investigated, and it was found that in the range 23–67°C the relative thermal conductivity was invariant with temperature within the experimental error (less than 1%). For a given concentration of 1-1 electrolyte, the relative thermal conductivity was found to vary linearly with the molecular weight of the solute.     

Hopping rates and concentrations of mobile fluoride ions in Pb(1-x)Sn(x)F(2) solid solutions

In the present paper, the ion dynamics and relaxation of fluoride ions in Pb(1-x)Sn(x)F(2) (with x=0.2-0.6) solid solutions, prepared by mechanochemical milling, are studied in the conductivity formalism over wide ranges of frequencies and temperatures. The conductivity spectra of the investigated materials are analyzed by the Almond-West (AW) power-law model. The estimated values of the hopping rates and the dc conductivity of different compositions are thermally activated with almost the same activation energy. The calculated values of the concentration of mobile ions, n(c), are almost independent of temperature and composition for x=0.2-0.4. The maximum value of n(c) is obtained for the x=0.6 sample, although it does not show the maximum conductivity. Therefore, the composition dependence of the ionic conductivity of these solid solutions could be explained based on the extracted parameters. The results presented in the current work indicate that the AW model represents a reasonable approximation of the overall frequency-dependent conductivity behavior of the investigated materials. The conductivity spectra at different temperatures for each composition are successfully scaled to a single master curve, indicating a temperature-independent relaxation mechanism. For different compositions, however, the conductivity spectra cannot be scaled properly, indicating composition-dependent relaxation dynamics.     

The BIOREMA project—part 3: International interlaboratory comparison for bio-ethanol test methods

The main objective of the reference materials for biofuel specifications (BIOREMA) project is the development of two test materials (one bio-ethanol material and one biodiesel material) with well-established reference values. Of a series of three papers, this part describes the material preparation, homogeneity study, stability study, and characterisation of the bio-ethanol material. The test material thus obtained was used in an interlaboratory comparison (ILC) to assess current practices and comparability amongst laboratories providing bio-ethanol testing services. Only 13 participants provided data, resulting in a small dataset for evaluation. Further, it appeared that for a number of laboratories, there was not sufficient material for the determination of all requested parameters. In most cases, as far as the data permit, it can be concluded that the consensus values (based on participant’s results) are in good agreement with the reference or the BIOREMA values (obtained by NMIs participating in the project). For three parameters, namely ethanol content, water content, and density, there is good agreement between the reference and consensus values. For these parameters, the reproducibility standard deviation is close to, or even smaller than, the expanded uncertainty associated with the reference value. A number of parameters show very poor reproducibility, for example, pH_e, electrolytic conductivity, and acidity. The same applies to sodium and copper content, which are very low and therefore challenging parameters to measure accurately. The results of the ILC underpin the need for certified reference materials and demonstrate the requirement for more robust quality control to improve the precision and trueness of the results from testing laboratories.     

Conductivity of micellar solutions of ionic surfactants and surface conductivity of micelles

Within the effective medium model, a method is proposed for determining the surface conductivity of micelles. The known experimental data on the conductivity of aqueous sodium dodecyl sulfate micellar solutions are analyzed employing the developed approach. Specific surface conductivity λ_s of micelles is shown to be 10⁻⁸Ω⁻¹. The high values of λ_s are indicative of a noticeable contribution of the dense part of the electrical double layer, which is comparable with the contribution of its diffuse part, to the micellar solution conductivity. This estimate is strongly dependent on the initial information obtained in different studies. The marked influence of the micelle surface conductivity on the effective conductivity of micellar solutions allows one to put the question of the correctness of the method commonly used to determine the degree of counterion binding from the slopes of the dependences of the solution conductivity on the overall surfactant concentrations in the premicellar and micellar regions.