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Main text The need for quality assessment of anthropogenic impact on environmental pollution is increasing due to discharge from various industries, the use of chemicals in agriculture and the consumption of fossil fuels. Diminishing resources such as natural waters used for the cultivation of agricultural products, plant and animal habitats are under severe pollution pressure and are at constant risk. Several parameters, such as Pb, Cd, Ni, Hg were listed by Water Framework Directive in Directive (2008/105/EC) in the priority substances. Cadmium and Hg were identified as priority hazardous substances whereas As is an important contaminant for its potential toxicological and carcinogenic effects. An inter-comparison study is organised in EURAMET TC-MC in order to demonstrate the capability participants for measuring five elements in river water. The participants carried out measurements for analytes: Pb, Cd, Ni and As as mandatory elements, and Se as an optional one. Participants were asked to perform the measurements with respect to the protocol provided. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The molar mass M and isotopic composition (expressed in amount-of-substance fractions x( i Si) of the silicon isotopes 28Si, 29Si, and 30Si) of a new silicon crystal (notation: Si28-23Pr11) highly enriched in the 28Si isotope have been determined independently at PTB and NMIJ by measuring exactly the same sample solutions using both a high resolution multicollector-inductively coupled plasma mass spectrometer (MC-ICP-MS). This crystal will be used for the complementary determination of the Avogadro constant N A and thus providing one of many key parameters in the planned redefinition of the SI units kilogram and mole, using fundamental constants. Samples from three different axial positions in the crystal ingot, each divided into several radial positions were measured in order to probe possible variations of the molar mass and isotopic composition. Results obtained at PTB and NMIJ agreed within the limits of uncertainty. The application of the latest improved measurement techniques as well as an improved determination of the calibration factors (K) required to correct for mass bias effects resulted in an averaged M = 27.976 942 666(40) g mol−1 with a relative combined uncertainty u c,rel(M) = 1.4 × 10−9. The course of M as a function of the origin of the measured samples suggests no significant inhomogeneity within the limits of the claimed uncertainty throughout the crystal supporting its applicability for the determination of a new N A. This extends to x(28Si) and x(29Si). Variations in x(30Si) as a function of the sample location were observed, but a systematic relation to physical origins cannot be claimed. Compared to the previous silicon crystal ('AVO28', notation: Si28-10Pr11) used for the latest determination of N A, the enrichment increases from x(28Si) = 0.999 957 52(12) mol mol−1 ('AVO28') to x(28Si) = 0.999 984 470(39) mol mol−1 (Si28-23Pr11, discussed in this paper) which is at least in part responsible for a reduction of the associated measurement uncertainty u(M).

The determination of the mass fractions of bromide, sulfate, and lead as well as the isotopic composition of the lead (expressed as the molar mass and the amount fractions of all four stable lead isotopes) in an aqueous solution of sodium chloride with a mass fraction of 0.15 g/g was the subject of this comparison. Even though the mass fractions ranged from 3 μg/g (bromide) to 50 ng/g (lead), almost all results reported agreed with the according KCRVs. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Improved measurements on silicon crystal samples highly enriched in the 28Si isotope (known as 'Si28' or AVO28 crystal material) have been carried out at PTB to investigate local isotopic variations in the original crystal. This material was used for the determination of the Avogadro constant NA and therefore plays an important role in the upcoming redefinition of the SI units kilogram and mole, using fundamental constants. Subsamples of the original crystal have been extensively studied over the past few years at the National Research Council (NRC, Canada), the National Metrology Institute of Japan (NMIJ, Japan), the National Institute of Standards and Technology (NIST, USA), the National Institute of Metrology (NIM, People's Republic of China), and multiple times at PTB. In this study, four to five discrete, but adjacent samples were taken from three distinct axial positions of the crystal to obtain a more systematic and comprehensive understanding of the distribution of the isotopic composition and molar mass throughout the crystal. Moreover, improved state-of-the-art techniques in the experimental measurements as well as the evaluation approach and the determination of the calibration factors were utilized. The average molar mass of the measured samples is M??=??27.976 970 12(12) g mol?1 with a relative combined uncertainty uc,rel(M)??=??4.4 ×10?9. This value is in astounding agreement with the values of single samples measured and published by NIST, NMIJ, and PTB. With respect to the associated uncertainties, no significant variations in the molar mass and the isotopic composition as a function of the sample position in the boule were observed and thus could not be traced back to an inherent property of the crystal. This means that the crystal is not only 'homogeneous' with respect to molar mass but also has predominantly homogeneous distribution of the three stable Si isotopes.

Within the Working Group on Inorganic Analysis (IAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) international key comparisons and pilot studies related to inorganic analysis are carried to ensure consistency in this field at the highest level. Some of these comparisons deal directly with the preparation and characterization of monoelemental solutions or with topics, closely related. The importance of monoelemental solutions lies in the fact that almost every measurement in inorganic analysis relies on the comparison with either a reference material, or references in form of solutions, usually (mono)elemental solutions. All quantitative measurement approaches, e.g. isotope dilution or standard addition, need an accurate reference solution made from a well characterized reference material, prepared under full gravimetric control. These primary (monoelemental) solutions do not only serve as arbitrary references/calibration solutions, but they also link up measurement results to the International System of units (SI), this way establishing the so-called metrological traceability to a measurement unit of the SI. Without such solutions on the highest possible level of accuracy and with the smallest possible associated uncertainties (for e.g. element content and/or impurities), an analysis itself can never be as good as it could be with appropriate reference solutions. This article highlights select key comparisons and pilot studies dealing with monoelemental solution-related topics within the IAWG from the foundation of CCQM—25 years ago—up to latest achievements in the field of inorganic analysis.

ICP-MS has played a key role in inorganic chemical metrology for 25 years, from the 1993 CIPM feasibility study which led to establishment of the CCQM. Since that time, the Inorganic Analysis Working Group of the CCQM has organised 56 international comparisons involving measurements by ICP-MS and, in a recent comparison, 16 different national institutes submitted their results using the technique. Metrological applications of ICP-MS currently address an enormous range of measurements using a wide variety of instrumentation, calibration strategies and methodologies. This review provides an overview of the ICP-MS field with an emphasis on developments which are of particular relevance to chemical metrology. Examples from CCQM comparisons and the services available from the participants are used to illustrate how the capability and scope of ICP-MS methods have expanded far beyond the expectations of 1993. This is due in part to the research and development Programmes of the national institutes which participate in the CCQM. They have played a key role in advancing new instrumentation and applications for elemental analysis, isotope dilution mass spectrometry, determination of isotopic ratio or composition, and speciation of organometallic compounds. These developments are continuing today, as demonstrated by work in new fields such as heteroatom quantitation of proteins, characterisation and counting of nanoparticles using spICP-MS, and LA-ICP-MS analysis of solid materials.

Within the scope of re-determining the Avogadro constant, the content of impurities in ultra-pure, mono-isotopically enriched silicon 'Si28' was measured by infrared spectrometry. The calibration factors required for the calculation of the concentrations from the maximum absorption coefficients had to be determined in this context for the isotopically enriched material. For this purpose a model was prepared, which enables conversion of the factors for Si with natural isotopic abundance. On the basis of these results, the concentrations of the three most decisive impurities in the enriched material were determined. These are oxygen atoms on interstitial sites and substituting carbon and boron atoms which occupy silicon sites. Whereas carbon and oxygen were measured in accordance with standardized procedures modified for the particular metrological use, the absorption measurement of the boron was carried out differently to the conventional standard. The concentrations determined for the three types of crystal impurities are high enough to make a correction of the lattice parameter for the 'Si28' material necessary.

This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10−8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol−1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10−8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.

The molar mass of a new silicon crystal material highly enriched in 28Si ('Si28', x(28Si) >99.99%) has been measured for the first time using a combination of a modified isotope dilution mass spectrometry (IDMS) technique and a high resolution multicollector-ICP-mass spectrometer. This work is related to the redetermination of the Avogadro constant NA with an intended relative measurement uncertainty urel(NA) ≤ 2 × 10−8. The corresponding experimental investigations of the International Avogadro Coordination (IAC) were performed using this novel 'Si28' material. One prerequisite of the redetermination of NA is the determination of the isotopic composition and thus molar mass of 'Si28' with urel(M('Si28')) ≤ 1 × 10−8. At PTB, a molar mass M('Si28') = 27.976 970 27(23) g mol−1 has been determined with an associated relative uncertainty urel(M('Si28')) = 8.2 × 10−9, opening the opportunity to reach the target uncertainty of NA.

To determine the Avogadro constant by counting the atoms in quasi-perfect spheres made of a silicon crystal highly enriched with 28Si, the isotopic composition of the crystal was measured in different laboratories by different measurement methods. This paper examines the consistency of the measurement results.

A new method applying isotope dilution mass spectrometry to determine the molar mass of a silicon sample, highly enriched with respect to 28Si, has been proposed recently. This paper describes a different way of calculating the molar mass by solving an equation linking the measurement results to the ratio between the amount-of-substance fractions of 28Si and 30Si in the sample. The mathematical model and the final measurement equation are much more straightforward than those previously reported, though fully equivalent.

Elements in human serum serve as important biomarkers and their levels reflect the well-being of an individual. Electrolytes such as sodium (Na) and chloride (Cl) are crucial in maintaining the normal distribution of water, osmotic pressure and electrical neutrality in the body. Trace element such as copper (Cu) plays a part in many oxidation-reduction reactions and metalloenzymes. The majority of selenium (Se) exists as selenoproteins which are cofactors in the glutathione peroxidase activity that protects the body against free radicals. Phosphorus (P) is required for strong bones and teeth. It is also indispensable for growth, maintenance and repair of tissues and cells. The key comparison CCQM-K139: elements in human serum was coordinated by the Health Sciences Authority, Singapore. This comparison aimed to enable participating National Metrology Institutes (NMIs) and Designated Institutes (DIs) to demonstrate their competence in the determination of elements (electrolytes and essential elements) in human serum. The five measurands (Na, Cl, Cu, Se and P) selected for this comparison were not covered in the last two comparisons in the clinical area (CCQM-K14 and CCQM-K107) and offered different analytical challenges. Their concentration levels were within the normal biological range. They were also within the range of existing calibration and measurement capability (CMC) claims in the International Bureau of Weights and Measures' Key Comparison Database (BIPM KCDB). Ten institutes participated in the comparison for Na, eight for Cl, eleven for Cu, six for Se and eight for P. For the analysis of Na, Cu, Se and P, most of the participating institutes employed microwave-assisted digestion and acid digestion (with or without heating) sample dissolution. For the analysis of Cl, in addition to the microwave-assisted digestion and acid digestion, a wider variety of techniques were employed. These included matrix separation, alkaline extraction and coulometric titration. Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were the two most commonly used instrumental techniques. Other techniques used included ion chromatography (IC), flame atomic absorption spectrometry (FAAS), titration and micro-coulometry. The medians were used as the estimators of Key Comparison Reference Values (KCRVs) for all measurands. The KCRVs (± standard uncertainty) for Na, Cl, Cu, Se and P (in mg/kg) were 3346 (± 14), 3871 (± 22), 1.151 (± 0.007), 0.1292 (± 0.0007) and 125.70 (± 0.35), respectively. The k-factor of 2 was used for the estimation of the expanded uncertainties of the KCRVs. The degree of equivalence and its associated uncertainty were calculated for each submitted result. For the five measurands, most participating institutes were able to demonstrate their capabilities in the determination of elements in human serum. CMC claims based on elements covered in this study may include other elements with similar core competencies, such as zinc (Zn), potassium (K), magnesium (Mg), calcium (Ca) and iron (Fe), in a wide range of biological materials. The measurands should be at similar concentration range and analysed using the same measurement technique(s) applied in this key comparison. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Cosmetics are used in practically all walks of life as a means of improving skin and beautifying complexion. In recent years, more and more attention has been paid to the cosmetic safety. In response to the cosmetic safety issue, the accurate measurement of the heavy metals in cosmetics is, therefore, particularly important. NMIs from different countries should establish their chemical metrology traceability system in this area, which includes both measurement methods research and certain CRMs development. It should be noted that because the matrix of many cosmetics is complex and the contents of the heavy metals are relatively low, it still is a challenging task to measure the analytes with high accuracy and precision. CCQM-K106 followed up CCQM pilot study 'CCQM-P128: Pb, As measurements in cosmetic (cream)' coordinated by the National Institute of Metrology, China (NIM) in 2009. The cream was selected as the testing material, which is widely used as a daily skin care worldwide. This is the first CCQM key comparison regarding the measurement of toxic metal elements with the cosmetic matrix, which includes pure water, liquid paraffin, silicone oil, synthetic squalane, hyaluronic acid, glycerin, propylene glycol, allantoin, preservative and so on. The aim of the CCQM-K106 is to demonstrate the capability of participating NMIs and designated institutes in measuring the contents of poisonous elements, including lead, arsenic and mercury in a cosmetic sample (cream), and support CMC claims relating to inorganic elements in cosmetic materials and similar chemical industry products. The cream matrix sample was prepared under the guidance of professional technicians. The formula of the cream was carefully chosen to match with a real cosmetic. The homogeneity and stability level of Pb, As and Hg in the cream sample were fit for the objective of the comparison. Each participant received two numbered bottles containing about 5g samples in each bottle. The instruction relating to CCQM-K106 was sent to each participant by e-mail, which consisted of technical protocol, results report form and inorganic core capabilities tables. The results were reported as mass faction (mg/kg). Calculation of the uncertainty expressed as a combined standard uncertainty and an expanded uncertainty at 95% confidence. In order to allow a sufficient evaluation of the comparison, the report was required to include a detailed description of the applied method of measurement, information about sample digestion and preparation, information about the reference material used for calibration. The methods of measurement were free to be selected by the participants. For the sample treatment, most of the participants used microwave digestion method. For instrumental determination, a variety of techniques such as ICP-MS, AAS, INAA were adopted by the participants. Most participants choose ID-ICP-MS method to measure Pb and Hg, which showed the better performance in terms of consistency and reliability of the measurement results. The reference mass fraction values and associated uncertainties were calculated by different statistic ways. As the result, the median and uncertainty of median were proposed as the key comparison reference value (KCRV) and its associated key comparison reference uncertainty after removal of suspected extreme values. In general, the performances of the majority of the CCQM-K106 participants are excellent, illustrating their measurement capability for Pb, As and Hg in a complex greasy matrix. The results can be used further by any participant to support its CMC claim at least for a borate buffer. That claim will concern the pH method employed by the participant during this comparison and will cover the used temperature(s) or the full temperature range between 15?C and 37 ?C for the participant which measured pH values at the three temperatures. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Isotope amount ratios are proving useful in an ever increasing array of applications that range from studies unravelling transport processes, to pinpointing the provenance of specific samples as well as trace element quantification by using isotope dilution mass spectrometry (IDMS). These expanding applications encompass fields as diverse as archaeology, food chemistry, forensic science, geochemistry, medicine and metrology. However, to be effective tools, the isotope ratio data must be reliable and traceable to enable the comparability of measurement results. The importance of traceability and comparability in isotope ratio analysis has already been recognized by the Inorganic Analysis Working Group (IAWG) within the CCQM. While the requirements for isotope ratio accuracy and precision in the case of IDMS are generally quite modest, 'absolute' Pb isotope ratio measurements for geochemical applications as well as forensic provenance studies require Pb isotope ratio measurements of the highest quality. To support present and future CMCs on isotope ratio determinations, a key comparison was urgently needed and therefore initiated at the IAWG meeting in Paris in April 2011. The analytical task within such a comparison was decided to be the measurement of Pb isotope amount ratios in water and bronze. Measuring Pb isotope amount ratios in an aqueous Pb solution tested the ability of analysts to correct for any instrumental effects on the measured ratios, while the measurement of Pb isotope amount ratios in a metal matrix sample provided a real world test of the whole chemical and instrumental procedure. A suitable bronze material with a Pb mass fraction between 10 and 100 mg•kg-1 and a high purity solution of Pb with a mass fraction of approximately 100 mg•kg-1 was available at the pilot laboratory (BAM), both offering a natural-like Pb isotopic composition. The mandatory measurands, the isotope amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb) and n(208Pb)/n(204Pb) were selected such that they correspond with those commonly reported in Pb isotopic studies and fully describe the isotopic composition of Pb in the sample. Additionally, the isotope amount ratio n(208Pb)/n(206Pb) was added, as this isotope ratio is typically measured when performing Pb quantitation by IDMS involving a 206Pb spike. Each participant was free to use any method they deemed suitable for measuring the individual isotope ratios. However, the majority of the results were obtained by using muIti-collector ICPMS or TIMS. The key requirements for all analytical procedures were a traceability statement for all results and the establishment of an uncertainty budget meeting a target uncertainty for all ratios of 0.2 %, relative (k=1). Additionally, the use of a Pb-matrix separation procedure was encouraged. The obtained overall result was excellent, demonstrating that the individual results reported by the NMIs/DIs were comparable and compatible for the determination of Pb isotope ratios. MC-ICPMS and MC-TIMS data were consistent with each other and agree to within 0.05 %. The corresponding uncertainties can be considered as realistic uncertainties and mainly range from 0.02 % to 0.08 % (k=1). As stated above isotope ratios are being increasingly used in different fields. Despite the availability and ease of use of new mass spectrometers, the metrology of unbiased isotope ratio measurements remains very challenging. Therefore, further comparisons are urgently needed, and should be designed to also engage scientists outside the NMI/DI community. Possible follow-up studies should focus on isotope ratio and delta measurements important for environmental and technical applications (e.g. B), food traceability and forensics (e.g. H, C, N, O, S and 87Sr/86Sr) or climate change issues (e.g. Li, B, Mg, Ca, Si). Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM.

High purity elements can serve as a realization of the SI unit amount of substance for the specific element. Solutions prepared from high purity metals by applying gravimetric preparation and the concept of molar mass are used as 'calibration' solutions in many fields of analytical chemistry and provide the metrological basis in elemental analysis. Since ideal purity does not exist for real materials, the actual purity of the high purity material must be known with a specified uncertainty. As required uncertainties around 10?4 relative on the purity statement are not accessible in almost all cases by a direct measurement of the element in itself, the indirect approach is followed, where all elements excepting the matrix element itself are measured and their sum is subtracted from the value for ideal purity, which is 1 kg/kg. It was the aim of this comparison to demonstrate the capability of national metrology institutes and designated institutes to determine the purity of pure elements. In order to limit the effort within this comparison, only six metallic impurities (Ag, Al, Cd, Cr, Ni, Tl) in the low mg/kg range are considered in a zinc matrix. It has to be underlined here that the task was to measure the purity of zinc based on the determination of six analytes. The task is not trace analysis of specific analytes in zinc. This subtle distinction defines different measurands. The sample, pure Zn, was cut in pieces of cubic geometry for wet chemical analysis or of pin geometry for GDMS analysis and was sent to the participants. The comparison was run under the auspices of the Inorganic analysis Working Group (IAWG) of the CCQM and was piloted by the BAM Federal Institute for Materials Research and Testing, Berlin, Germany. The majority of the participants applied ICP-MS techniques and only two participants used additionally atomic absorption spectrometry. GDMS was used only by one participant. The observed spreads for the measurement results reported by the participants were significantly lower than those of the preceding study CCQM-P107 and were well below the target uncertainty of 30% relative. As a consequence, comparability within the participating laboratories is demonstrated to be established. The individual measurement results, mean values and medians derived were in all cases very consistent with the reference values obtained by IDMS and so the accuracy of the measurement results for the participating laboratories is as well demonstrated to be established. Especially with the results of CCQM-P62 and CCQM-P107 in mind, the outcome of CCQM-K72 can be considered as a big step forward in the community. CCQM is aware of the difference between a characterization based on only six analytes and a complete characterization. Therefore, the pilot study CCQM-P149 has been initiated and already started, which focuses on the fit-for-purpose approaches for the purity determination of metals (here: zinc) to be used as primary standards in elemental analysis. Another follow-up in the form of a pilot study on non-metal impurities is mandatory, because non-metal impurities such as oxygen, nitrogen and sulfur often make up the largest contributions. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The increase in renewable sources in the energy matrix of the countries is an effort to reduce dependency on crude oil and the environmental impacts associated with its use. In order to help overcome the lack of widely accepted quality standards for fuel ethanol and to guarantee its competitiveness in the international trade market, the NMIs have been working to develop certified reference materials for bio-fuels and measurement methods. Inorganic impurities such as Cu, Na and Fe may be present in the fuel ethanol and their presence is associated with corrosion and the formation of oxide deposits in some engine parts. The key comparison CCQM-K100 was carried out under the auspices of the Inorganic Analysis Working Group (IAWG) and the coordination of the National Institute of Metrology, Quality and Technology (INMETRO). The objective of this key comparison was to compare the measurement capabilities of the participants for the determination of Cu in fuel ethanol. Ten NMIs participated in this exercise and most of them used the isotopic dilution method for determining the amount of Cu. The median was chosen as key comparison reference value (KCRV). The assigned KCRV for the Cu content was 0.3589 ?g/g with a combined standard uncertainty of 0.0014 ?g/g. In general, there is a good agreement among the participants' results. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The key comparison CCQM-K89 was undertaken to demonstrate the capability of participating NMIs and DIs in measuring the contents of incurred trace elements (total arsenic, cadmium and lead) and essential elements (calcium and zinc) at ?g/g (for arsenic, cadmium, lead and zinc) and mg/g (for calcium) levels in a herb matrix sample by various analytical techniques. This key comparison was organized by the Government Laboratory of the Hong Kong Special Administrative Region (GLHK) and agreed at the Inorganic Analysis Working Group Meeting in Hind?s, Sweden in October 2010 as a benchmarking exercise with arsenic (a trace element) and calcium (an essential element) chosen as the 'exemplary' elements. It was also agreed that a pilot study CCQM-P126 would be run in parallel with this key comparison. The key comparison serves to facilitate claims by participants on the Calibration and Measurement Capabilities (CMCs) as listed in Appendix C of the Key Comparison Database (KCDB) under the Mutual Recognition Arrangement of the International Committee for Weights and Measures (CIPM MRA). A total of 20 NMIs/DIs registered for this programme and 18 of them submitted their results. Most of the participants used microwave acid digestion methods for sample dissolution. For the instrumental determination, a variety of techniques like ICP-MS, AAS, INAA, ICP-AES were employed by the participants. For this key comparison, inorganic core capabilities have been demonstrated by concerned participants with respect to methods including ICP-MS (without isotope dilution), ID-ICP-MS, ICP-AES, INAA, AAS and ion chromatography with iteratively matrix-matched calibration on the determination of total arsenic, calcium, cadmium, lead and zinc in a matrix of herb. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The aim of this comparison was to demonstrate the capability of national metrology institutes to measure elemental mass fractions at a level of w(E) ≈ 1 g/kg as found in almost all mono-elemental calibration solutions. These calibration solutions represent an important link in traceability systems in inorganic analysis. Virtually all traceable routine measurements are linked to the SI through these calibration solutions. Every participant was provided with three solutions of each of the three selected elements chromium, cobalt and lead. This comparison was a joint activity of the Inorganic Analysis Working Group (IAWG) and the Electrochemical Analysis Working Group (EAWG) of the CCQM and was piloted by the Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany) with the help of the Bundesanstalt fur Materialforschung und -prufung (BAM, Berlin, Germany), the Centro Nacional de Metrologia (CENAM, Queretaro, Mexico) and the National Institute of Standards and Technology (NIST, Gaithersburg, USA). A small majority of participants applied inductively coupled plasma optical emission spectrometry (ICP OES) in combination with a variety of calibration strategies (one-point-calibration, bracketing, calibration curve, each with and without an internal standard). But also IDMS techniques were carried out on quadrupole, high resolution and multicollector ICP-MS machines as well as a TIMS machine. Several participants applied titrimetry. FAAS as well as ICP-MS combined with non-IDMS calibration strategies were used by at least one participant. The key comparison reference values (KCRV) were agreed upon during the IAWG/EAWG meeting in November 2011 held in Sydney as the added element content calculated from the gravimetric sample preparation. Accordingly the degrees of equivalence were calculated. Despite the large variety of methods applied no superior method could be identified. The relative deviation of the median of the participants' results from the gravimetric reference value was equal or smaller than 0.1% (with an average of 0.05%) in the case of all three elements. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This comparison 'Hg in natural water' was a follow-up to the pilot studies CCQM-P100.1 and CCQM-P100.2. The aim of this comparison was to demonstrate the capability of national metrology institutes to measure the Hg mass concentration in a natural water sample at the very low concentration level of ?(Hg) ? 70 ng/L as required by the EQS. In this way it served to help implement the European Water Framework Directive (WFD). This comparison was an activity of the Inorganic Analysis Working Group (IAWG) of CCQM and was piloted by Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany) with the help of the co-organizers Bundesanstalt f?r Materialforschung und -pr?fung (BAM, Berlin, Germany), Laboratoire National de M?trologie et d'Essais (LNE, Paris, France), and the Joint Research Centre?Institute for Reference Materials and Measurements (EC?JRC?IRMM, Geel, Belgium). The following laboratories participated in this key comparison (in alphabetical order): BAM (Germany) EC?JRC?IRMM (European Union) KRISS (Republic of Korea) LGC (United Kingdom) LNE (France) NIST (United States of America) NMIA (Australia) NRC (Canada) PTB (Germany) SP (Sweden) The majority of participants applied isotope dilution mass spectrometry (IDMS) using sector field or quadrupole inductively coupled plasma MS (ICP-MS) in combination with cold vapour (CV) generation as the analytical technique. NRC reported a combined result of ID-CV-ICP-MS and CV atomic absorption spectrometry (CV-AAS). SP applied a standard addition method on a sector field ICP-MS, while BAM made use of an external 5-point calibration on a CV atomic fluorescence spectrometer (AFS). The key comparison reference value (KCRV) was agreed upon during the IAWG meeting in April 2010 at BIPM as the sum of the added Hg content calculated from the gravimetric sample preparation and the Hg matrix content of the water used for sample preparation (determined and validated on two independent pathways). Accordingly the degrees of equivalence were calculated. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).