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Main text The key comparison CCQM-K68.2019 was aimed at evaluating the level of comparability of laboratories' capabilities for preparing nitrous oxide in air primary reference mixtures at ambient amount fractions, in the range 320 nmol mol−1 to 350 nmol mol−1. The comparison was coordinated by the BIPM and the KRISS. It consisted in the simultaneous comparison of a suite of 2n primary gas standards, two standards to be prepared by each of the n participating laboratories. Two independent analytical methods were used by the BIPM to analyse the amount fraction of N2O in air, namely Gas Chromatography with an Electron Capture Detector (GC−ECD) and Quantum Cascade Laser Absorption Spectroscopy (QCLAS). Since the circulation of the Draft A report in April 2021, four meetings took place with participants to discuss the mathematical treatment of the comparisons results, and several models were proposed. The model chosen by participants is the Bayesian Errors−In−Variables regression with shades of dark uncertainty. In this final report, the Key Comparison Reference Values were obtained with this model, with calculations performed by B Toman and A Possolo. The key comparison CCQM-K68.2019 is considered to present an analytical challenge and therefore classified as Track C comparison in the CCQM nomenclature. 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).

Main text The Pilot Study CCQM-P206 was conducted in parallel with the Key Comparison CCQM-K68.2019, which was aimed at evaluating the level of comparability of laboratories' capabilities for nitrous oxide in air primary reference mixtures at ambient amount fractions, in the range 320 nmol mol−1 to 350 nmol mol−1. The Pilot Study was set up to allow the participation of the Scripps Institution of Oceanography of the University of California San Diego (SIO/UCSD) as guest expert laboratory of the CCQM. The SIO/UCSD was invited by the CCQM in view of its long experience in accurate measurements of nitrous oxide in the atmosphere and is the calibration laboratory for this compound in the AGAGE (Advanced Global Atmospheric Gases Experiment) global measurement network. The laboratory has developed a unique method which provides an independent assessment of the N2O amount fraction compared to participants in CCQM-K68.2019. Its participation was also seen as the occasion to contribute to a more general reflexion on the compared advantages of two different systems to ensure traceability: a unique scale maintained by one central laboratory, or the dissemination of materials all traceable to the SI by multiple national metrology institutes. The comparison CCQM-K68.2019 was coordinated by the BIPM and the KRISS. It consisted in the simultaneous comparison of a suite of 2n primary gas standards, two standards to be prepared by each of the n participating laboratories. Two independent analytical methods were used by the BIPM to analyse the amount fraction of N2O in air, namely Gas Chromatography with an Electron Capture Detector (GC−ECD) and Quantum Cascade Laser Absorption Spectroscopy (QCLAS). For the Pilot Study, SIO/UCSD provided results of measurements of the N2O amount fraction in the two standards submitted by the Global Monitoring Laboratory of the National Oceanic and Atmospheric Administration (NOAA), a participant in the Key Comparison. Therefore, this study consists in looking at the agreement between SIO/UCSD measurement results and the Key Comparison reference value. All details on the Key Comparison CCQM-K68.2019, including its protocol and its results, can be found in its report. This report focuses on SIO/UCSD results and agreement with participants in the Key Comparison. 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).

Main text Under the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a pilot study, CCQM-P55.2.2018, was coordinated by the Bureau International des Poids et Mesures (BIPM), the Health Sciences Authority (HSA) of Singapore and the Chinese National Institute of Metrology (NIM). Three Metrology Institutes or Designated Institutes and the BIPM participated. Participants were required to assign the mass fraction of hexapeptide of HbA0 (VE) present as the main component in the comparison sample for CCQM-P55.2.2018. The comparison samples were prepared by HSA/BIPM from synthetic VE purchased from a commercial supplier and used as provided without further treatment or purification. VE was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of chemically synthesized peptides of known sequence, without cross-links, up to 5 kDa and without modification. It was anticipated to provide an analytical measurement challenge representative for the value-assignment of compounds of broadly similar structural characteristics. The majority of participants used amino acid analysis (PICAA) or quantitative nuclear magnetic resonance (PICqNMR) spectroscopy with a correction for structurally related peptide impurities. It was decided to assign reference values (RVs) based on the KCRVs of CCQM-K115.2018 for both the VE mass fraction and the mass fraction of the peptide-related impurities as indispensable contributor regardless of the use of PICAA, mass balance or any other approach to determine the VE purity. This allowed participants to demonstrate the efficacy of their implementation of the approaches used to determine the VE mass fraction. In particular, it allows participants to demonstrate the efficacy of their implementation of peptide-related impurity identification and quantification. More detailed studies on the identification/quantification of peptide related impurities revealed that the integrity of the impurity profile of the related peptide impurities obtained by the participant is crucial for the impact on accuracy of the VE mass fraction assignment. The assessment of the mass fraction of peptide impurities is based on the assumption that only the most consistent set of results is taken for the calculation of the RVPepImp. The sum of the combined cis/trans VE depsipeptide impurities (only identified/quantified by NRC and confirmed by BIPM and HSA) and mass fractions of peptide-related impurities that have been identified by at least two participants have been used to establish the RVPepImp. The RVPepImp of 53.0 mg/g is associated with a corresponding expanded uncertainty of 17.3 mg/g (k = 2) providing a more realistic basis of evaluation for the capabilities of the participants to identify/quantify peptide related impurities. Inspection of the degree of equivalence plots for the mass fraction of peptide impurities and additional information obtained from the peptide-related impurity profile indicates that in all cases the major related peptide impurity, VE depsipeptide, has not been identified. The VE depsipeptide impurity was initially and uniquely identified and quantified by the NRC by the use of 1H-NMR in the parallel CCQM-K115.2018. The related peptide impurity mass fraction results of only four participants (NRC, LGC, LNE and HSA) are in agreement with the RVPepImp. The NRC has identified and quantified the VE depsipeptide whereas the LGC, LNE and HSA have not identified the VE depsipeptide but accounted for that contribution. The approach selected to obtain a RVVE for the mass fraction of VE is based on a mass balance calculation that takes into account the most consistent set of results for the peptide-related impurities RVPepImp, TFA mass fraction and the water mass fraction. The RVVE based on CCQM-K115.2018 is 613 mg/g with a corresponding expanded uncertainty of the RVVE of 20 mg/g (k = 2). Inspection of the degree of equivalence plots for the mass fraction of VE shows that all results obtained by PICAA agree with the RVVE while the result obtained by the BIPM with PICqNMR disagrees with the RVVE. 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).

Main text Under the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a pilot study, CCQM-P55.2.c, was coordinated by the Bureau International des Poids et Mesures (BIPM), the Health Sciences Authority (HSA) of Singapore and the Chinese National Institute of Metrology (NIM). Three Metrology Institutes or Designated Institutes and the BIPM participated. Participants were required to assign the mass fraction of glycated hexapeptide of HbA1c (GE) present as the main component in the comparison sample for CCQM-P55.2.c. The comparison samples were prepared by HSA/BIPM from synthetic GE purchased from a commercial supplier and used as provided without further treatment or purification. GE was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of chemically synthesized peptides of known sequence, without cross-links, up to 5 kDa and modification (mono-glycation). It was anticipated to provide an analytical measurement challenge representative for the value-assignment of compounds of broadly similar structural characteristics. The majority of participants used amino acid analysis (PICAA) or quantitative nuclear magnetic resonance (PICqNMR) spectroscopy with a correction for structurally-related peptide impurities. It was decided to assign reference values (RVs) based on the KCRVs of CCQM-K115.c for both the GE mass fraction and the mass fraction of the peptide related impurities as indispensable contributor regardless of the use of PICAA, mass balance or any other approach to determine the GE purity. This allowed participants to demonstrate the efficacy of their implementation of the approaches used to determine the GE mass fraction. In particular, it allows participants to demonstrate the efficacy of their implementation of peptide related impurity identification and quantification. More detailed studies on the identification/quantification of peptide related impurities revealed that the integrity of the impurity profile of the related peptide impurities obtained by the participant is crucial for the impact on accuracy of the GE mass fraction assignment. The assessment of the mass fraction of peptide impurities is based on the assumption that all results are directly taken for the calculation of the RVPepImp by use of random-effects meta-analysis (DerSimonian-Laird (DSL) variance-weighted mean). The RVPepImp of 45.4 mg/g is associated with a corresponding expanded uncertainty of 9.5 mg/g (k =2.26) providing a more realistic basis of evaluation for the capabilities of the participants to identify/quantify peptide related impurities. Inspection of the degree of equivalence plots for the mass fraction of peptide impurities and additional information obtained from the peptide related impurity profile indicates that in all cases the major related peptide impurities have been identified and quantified. The approach selected to obtain a RVGE for the mass fraction of GE is based on the DerSimonian-Laird (DSL) variance-weighted mean. The DSL mean takes into account the uncertainties of the results while introducing sufficient excess variance to allow for their observed dispersion resulting in a larger expanded uncertainty U(RVGE). The RVGE based on CCQM-K115.c is 628 mg/g with a corresponding expanded uncertainty of the RVGE of 27 mg/g (k =2.26). All GE mass fraction results are in agreement with the RVGE. 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).

Main text Under the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM-K115.c, was coordinated by the Bureau International des Poids et Mesures (BIPM), the Health Sciences Authority (HSA) of Singapore and the Chinese National Institute of Metrology (NIM). Nine Metrology Institutes or Designated Institutes and the BIPM participated. Participants were required to assign the mass fraction of the glycated hexapeptide of HbA1c (GE) present as the main component in the comparison sample for CCQM-K115.c. The comparison samples were prepared by HSA/BIPM from synthetic GE purchased from a commercial supplier and used as provided without further treatment or purification. GE was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of chemically synthesized peptides of known sequence, without cross-links, up to 5 kDa and modification (mono-glycation). It was anticipated to provide an analytical measurement challenge representative for the value-assignment of compounds of broadly similar structural characteristics. The majority of participants used amino acid analysis (PICAA) or quantitative nuclear magnetic resonance (PICqNMR) spectroscopy with a correction for structurally-related peptide impurities approach as the amount of material that has been provided to each participant (25 mg) is insufficient to perform a full mass balance based characterization of the material by a participating laboratory. The coordinators, the BIPM, the HSA and the NIM, were the laboratories to use the mass balance approach as they had more material available. It was decided to propose KCRVs for both the GE mass fraction and the mass fraction of the peptide-related impurities as indispensable contributor regardless of the use of PICAA, PICqNMR or mass balance to determine the GE purity. This allowed participants to demonstrate the efficacy of their implementation of the approaches used to determine the GE mass fraction. In particular, it allows participants to demonstrate the efficacy of their implementation of peptide-related impurity identification and quantification. More detailed studies on the identification/quantification of peptide-related impurities revealed that the integrity of the impurity profile of the related peptide impurities obtained by the participant is crucial for the impact on accuracy of the GE mass fraction assignment. The assessment of the mass fraction of peptide impurities is based on the assumption that that all results are directly taken for the calculation of the KCRVPepImp by use of random-effects meta-analysis (DerSimonian-Laird (DSL) variance-weighted mean). The KCRVPepImp of 45.4 mg/g is associated with a corresponding expanded uncertainty of 9.5 mg/g (k =2.26) providing a more realistic basis of evaluation for the capabilities of the participants to identify/quantify peptide-related impurities. Inspection of the degree of equivalence plots for the mass fraction of peptide impurities and additional information obtained from the peptide-related impurity profile indicates that in most cases the major related peptide impurities have been identified and quantified. The approach selected to obtain a KCRVGE for the mass fraction of GE is based on the DerSimonian-Laird (DSL) variance-weighted mean. The DSL mean takes into account the uncertainties of the results while introducing sufficient excess variance to allow for their observed dispersion resulting in a larger expanded uncertainty U(KCRVGE). The KCRVGE for CCQM-K115.c is 628 mg/g with a corresponding expanded uncertainty of the KCRVGE of 27 mg/g (k =2.26). All GE mass fraction results are in agreement with the KCRVGE. 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).

Main text The CCQM-K154.b comparison was coordinated by the Bureau International des Poids et Mesures (BIPM) and the Chinese National Institute of Metrology (NIM) on behalf of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) for National Measurement Institutes (NMIs) and Designated Institutes (DIs) which provide measurement services in organic analysis under the 'Comité International des Poids et Mesures' Mutual Recognition Arrangement (CIPM MRA) and/or have participated in the BIPM's Mycotoxin Metrology Capacity Building and Knowledge Transfer (MMCBKT) project as part of its "Metrology for Safe Food and Feed in Developing Economies" Capacity Building Programme. Gravimetrically-prepared solutions having an assigned mass fraction of specified organic analytes are routinely used to calibrate measurement processes for the quantification of the same analytes in matrix samples. Appropriate assignments of the property value and associated uncertainty of calibration solutions thus underpin the traceability of routine analysis and are critical for accurate measurements. Evidence of successful participation in relevant international comparisons is needed to document calibration and measurement capability claims (CMCs) made by national metrology institutes and designated institutes. In total, eleven NMIs/DIs participated in the Track C, Model II, Key Comparison CCQM-K154.b [Gravimetric preparation and value assignment of aflatoxin B1 (AfB1) in acetonitrile (ACN)] for emerging areas of global interest and innovation. Participants were requested to gravimetrically prepare calibration solutions and value assign the mass fractions, expressed in mg/kg, of aflatoxin B1 (AfB1) in the acetonitrile (ACN) solution. Study samples, with assigned values and associated uncertainties were prepared by the comparison participants and sent to the coordinating laboratory for comparison. The Key Comparison Reference Values (KCRVs), calculated form values measured by the coordinating laboratory based on calibrations obtained from independent gravimetrically prepared calibrant solutions, agreed with participants reported values, within their stated uncertainties. AfB1 was selected to be representative of polar aflatoxins. Aflatoxins are a class of mycotoxins generally produced by fungi of the genus Aspergillus. It was anticipated to provide a challenge representative for the gravimetrical preparation and value assignment of calibration solutions in the mass fraction range of 2 mg/kg to 50 mg/kg of mycotoxins with broadly similar structural characteristics. Nine participants of the MMCBKT programme were provided with a stock solution having a known AfB1 mass fraction and expanded uncertainty to use to gravimetrically prepare and value assign a calibration solution. Three NMIs/DIs also participated using their own calibration solutions. The use of in-house solutions required an additional capacity to undertake a fit-for-purpose purity assessment. NIM was the only NMI participating using both the MMCBKT based and their own in-house assigned solutions in order to connect the two different groups. It was decided to propose separate KCRVs for each of the two ampoules provided by the participating NMIs/DIs based on the AfB1 mass fraction. This allowed participants to demonstrate the efficacy of their implementation of the approaches used to gravimetrically prepare calibration solutions and to assess the AfB1 mass fraction. The majority of the AfB1 mass fraction KCRVs (wKCRV) for CCQM-K154.b spanned a mass fraction range of 2.02 mg/kg to 31.57 mg/kg. The relative expanded uncertainties U(wKCRV) ranged from 0.69 % to 2.93 %. Inspection of the degree of equivalence plots for the AfB1 mass fraction assignments in CCQM-K154.b indicated that there was an excellent agreement of results. Solely, the AfB1 mass fraction assignments of INRAP did not agree with the KCRVs. It was found that the samples were altered as a result of an acid contamination. 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).

Main text Under the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM-K115.2018, was coordinated by the Bureau International des Poids et Mesures (BIPM), the Health Sciences Authority (HSA) of Singapore and the Chinese National Institute of Metrology (NIM). Ten Metrology Institutes or Designated Institutes and the BIPM participated. Participants were required to assign the mass fraction of the hexapeptide of HbA0 (VE) present as the main component in the comparison sample for CCQM-K115.2018. The comparison samples were prepared by HSA/BIPM from synthetic VE purchased from a commercial supplier and used as provided without further treatment or purification. VE was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of chemically synthesized peptides of known sequence, without cross-links, up to 5 kDa and without modification. It was anticipated to provide an analytical measurement challenge representative for the value-assignment of compounds of broadly similar structural characteristics. The majority of participants used amino acid analysis (PICAA) with a correction for structurally-related peptide impurities approach as the amount of material that had been provided to each participant (25 mg) was insufficient to perform a full mass balance based characterization of the material by a participating laboratory. The coordinators, the BIPM, the HSA and the NIM, were the laboratories to use the mass balance approach as they had more material available. It was decided to propose KCRVs for both the VE mass fraction and the mass fraction of the peptide related impurities as indispensable contributor regardless of the use of PICAA, mass balance or any other approach to determine the VE purity. This allowed participants to demonstrate the efficacy of their implementation of the approaches used to determine the VE mass fraction. In particular, it allowed participants to demonstrate the efficacy of their implementation of peptide related impurity identification and quantification. More detailed studies on the identification/quantification of peptide related impurities revealed that the integrity of the impurity profile of the related peptide impurities obtained by the participant is crucial for the impact on accuracy of the VE mass fraction assignment. The assessment of the mass fraction of peptide impurities is based on the assumption that only the most consistent set of results is taken for the calculation of the KCRVPepImp. The sum of the combined cis/trans VE depsipeptide impurities (only identified/quantified by NRC and confirmed by BIPM and HSA) and mass fractions of peptide related impurities that have been identified by at least two participants have been used to establish the KCRVPepImp. The KCRVPepImp of 53.0 mg/g is associated with a corresponding expanded uncertainty of 17.3 mg/g (k = 2) providing a more realistic basis of evaluation for the capabilities of the participants to identify/quantify peptide related impurities. Inspection of the degree of equivalence plots for the mass fraction of peptide impurities and additional information obtained from the peptide related impurity profile indicates that in all cases the major related peptide impurity, VE depsipeptide, has not been identified. The VE depsipeptide impurity was initially and uniquely identified and quantified by the NRC by the use of 1H-NMR. The related peptide impurity mass fraction results of only four participants (NRC, LGC, LNE and HSA) are in agreement with the KCRVPepImp. The NRC has identified and quantified the VE depsipeptide whereas the LGC, LNE and HSA have not identified the VE depsipeptide but accounted for that contribution. The approach selected to obtain a KCRVVE for the mass fraction of VE is based on a mass balance calculation that takes into account the most consistent set of results for the peptide related impurities KCRVPepImp, TFA mass fraction and the water mass fraction. The KCRVVE for CCQM-K115.2018 is 613 mg/g with a corresponding expanded uncertainty of the KCRVVE of 20 mg/g (k = 2). 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).

Main text Under the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a pilot study, CCQM-P216, was coordinated by the Chinese National Institute of Metrology (NIM), National Research Council of Canada (NRC) and the Bureau International des Poids et Mesures (BIPM). Eleven Metrology Institutes or Designated Institutes and the BIPM participated in the first phase of the pilot study (Part 1). The purpose of this pilot study was to develop measurement capabilities for larger proteins using a recombinant humanized IgG monoclonal antibody against Spike glycoprotein of SARS-CoV-2 (Anti-S IgG mAb) in solution. The first phase of the study was designed to employ established methods that had been previously studies by the CCQM Protein Analysis Working Group, involving the digestion of protein down to the peptide or amino acid level. The global coronavirus pandemic has also led to increased focus on antibody quantitation methods. IgG are among the immunoglobulins produced by the immune system to provide protection against SARS-CoV-2. Anti-SARS-CoV-2 IgG can therefore be detected in samples from affected patients. Antibody tests can show whether a person has been exposed to the SARS-CoV-2, and whether or not they potentially show lasting immunity to the disease. With the constant spread of the virus and the high pressure of re-opening economies, antibody testing plays a critical role in the fight against COVID-19 by helping healthcare professionals to identify individuals who have developed an immune response, either via vaccination or exposure to the virus. Many countries have launched large-scale antibody testing for COVID-19. The development of measurement standards for the antibody detection of SARS-CoV-2 is critically important to deal with the challenges of the COVID-19 pandemic. In this study, the SARS-CoV-2 monoclonal antibody is being used as a model system to build capacity in methods that can be used in antibody quantification. Amino acid reference values with corresponding expanded uncertainty of 36.10 ± 1.55 mg/kg, 38.75 ± 1.45 mg/kg, 18.46 ± 0.78 mg/kg, 16.20 ± 0.67 mg/kg and 30.61 ± 1.30 mg/kg have been established for leucine, valine, phenylalanine, isoleucine and proline, respectively. Agreement between nearly all laboratories was achieved for the amino acid analysis within 2 to 2.5 %, with one participant achieving markedly higher results due to a technical issue found in their procedure; this result was thus excluded from the reference value calculations. The relatively good agreement within a laboratory between different amino acids was not dissimilar to previous results for peptides or small proteins, indicating that factors such as hydrolysis conditions and calibration procedures could be the largest sources of variability. Peptide reference values with corresponding expanded uncertainty of 4.99 ± 0.28 mg/kg and 6.83 ± 0.65 mg/kg have been established for ALPAPIEK and GPSVFPLAPSSK, respectively. Not surprisingly due to prior knowledge from previous studies on peptide quantitation, agreement between laboratories for the peptide-based analysis was slightly poorer at 3 to 5 %, with one laboratory's result excluded for the peptide GPSVFPLAPSSK. Again, this level of agreement was not significantly poorer than that achieved in previous studies with smaller or less complex proteins. To reach the main text of this paper, click on Final Report.

The key comparison CCQM-K137 was aimed at evaluating the level of compatibility of laboratories' preparative capabilities for gravimetric nitrogen monoxide/nitrogen primary reference mixtures at mole fractions of 30 μmol mol-1 and 70 μmol mol-1. The comparison was organised by the BIPM. It consisted in the simultaneous comparison of a suite of 2n primary gas standards, two standards to be prepared by each of the n participating laboratories at the nominal values of 30 μmol mol-1 and 70 μmol mol-1. Two independent analytical methods were used by the BIPM to analyse the amount fraction of nitrogen monoxide (NO) in nitrogen; UV spectrophotometry and chemiluminescence (CLD). The agreement between the results obtained with the two main techniques served to highlight possible issues in the preparation of the standards. During this comparison, standards prepared by two participants appeared to result in a larger bias between the analysers than observed for others. These observations were explained by the analysis of all standards by Fourier Transform Infrared Spectroscopy (FTIR) which identified the presence of a larger amounts of water vapour (H2O), nitrous oxide (N2O) and nitrogen dioxide (NO2) in these standards, which are the three main impurities which can appear in mixtures of NO in nitrogen. The above observations were used to underpin the selection of standards (at each nominal NO mole fraction) which can be considered as a consistent set, allowing the calculation of a calibration line by a Generalised Least-Square regression. Key Comparison Reference Values were then proposed for all participants as predicted values from the calibration lines. Interferences caused in the response of the CLD analyser by impurities (verified by FTIR measurements) led to only the results from the UV analyser being proposed for the KCRV and Degrees of Equivalence calculations. Good agreement was observed between all participants who could prepare their standards with minimum levels of impurities. The key comparison CCQM-K137 is considered to present an analytical challenge at both nominal mole fractions and therefore considered as a Specialised (Track C) comparison in the CCQM nomenclature. 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).

Ozone plays a crucial role in tropospheric chemistry, is the third largest contributor to greenhouse radiative forcing after carbon dioxide and methane and also a toxic air pollutant affecting human health and agriculture. Long-term measurements of tropospheric ozone have been performed globally for more than 30 years with UV photometers, all relying on the absorption of ozone at the 253.65 nm line of mercury. We have re-determined this cross-section and report a value of 11.27 × 10−18 cm2 molecule−1 with an expanded relative uncertainty of 0.84 %. This is lower than the conventional value currently in use and measured by Hearn in 1961 with a relative difference of 1.8%, with the consequence that historically reported ozone concentrations should be increased by 1.8%. In order to perform the new measurements of cross sections with reduced uncertainties, a system to generate pure ozone in the gas phase together with an optical system based on a UV laser with lines in the Hartley band, including accurate path length measurement of the absorption cell and a careful evaluation of possible impurities in the ozone sample by mass spectrometry and Fourier Transform Infrared spectroscopy was setup. This resulted in new measurements of absolute values of ozone absorption cross sections of 9.48 × 10−18, 10.44 × 10−18, and 11.07 × 10−18 cm2 molecule−1, with relative expanded uncertainties better than 0.6%, for the wavelengths (in vacuum) of 244.062, 248.32, and 257.34 nm respectively. The cross-section at the 253.65 nm line of mercury was determined by comparisons using a Standard Reference Photometer equipped with a mercury lamp as the light source. The newly reported value should be used in the future to obtain the most accurate measurements of ozone concentration, which are in closer agreement with non UV photometry based methods such as the gas phase titration of ozone with nitrogen monoxide.

A novel and convenient method of monitoring the internal surface area of porous silicon layers grown on either n-type or p-type silicon is described. The method involves measurement of the interfacial capacitance under conditions where electrons accumulate at the electrode surface. The technique has been used to study the growth and leaching of porous silicon layers in hydrofluoric acid/ethanol. The changes in the interfacial capacitance have been related to the development of photoluminescence.

Voltage-dependent tuning of photoluminescence (PL) and electroluminescence (EL) spectra of porous silicon layers grown on n+ and n− substrates has been studied using electrolyte contacts. It has been demonstrated that PL and EL tuning occur under accumulation conditions. A mechanism that explains both PL and EL tuning is proposed on the basis of a kinetic; “scheme of squares” that considers incremental electron injection into quantum-confined particles, leading to Auger quenching of photoexcited or electrochemically generated electron-hole pairs. The tuning effects are predicted to occur as a consequence of the dependence of electron accumulation on the energy of the conduction band, which is turn related to particles size. PL and EL spectra have been simulated for an ensemble of particles of different sizes, and it is shown that the model correctly predicts all the experimentally observed characteristics of the voltage tuning.

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.

Electroluminescence has been observed using the photostimulated reduction of persulfate ions at porous silicon layers grown on p−‐Si substrates. Electrons were generated in the substrate by illumination from the ohmic contact side. The detection of visible electroluminescence shows that photogenerated electrons accumulate in the porous layer when the p− substrate is reverse biased. Voltage tuning of the electroluminescence spectrum was observed, but the tuning saturated when the reduction of persulfate became light limited. The tuning is attributed to the switching on of electroluminescence as electrons progressively populated particles of decreasing size, followed by switching off by Auger quenching when a second electron is captured before radiative decay occurs.

A novel and convenient method of monitoring the internal surface area of a porous silicon layer formed on an n‐type substrate has been developed. The technique has been employed during electrochemical growth and subsequent chemical leaching of porous silicon layers in hydrofluoric acid/ethanol. The method involves periodic interruption of the anodization current to allow in situ measurement of the interfacial capacitance under forward bias using a triangular voltage wave form. The observed evolution of the internal surface area is related to the development of photoluminescence.

The deposition of Cu onto Au(100) and of Pb onto n- Si(111) electrodes from aqueous solutions has been monitoredin situby scanning tunneling microscopy. In the first case, a bcc structure of the Cu overlayer is observed, which allows pseudomorphic growth on Au(100) up to the 10th layer. Then a slow structural transition to fee begins. In contrast, Pb on Si(111) is shown to deposit as 3D crystallites with flat (111) terminated surfaces.

A report is given of the sixth meeting of the Consultative Committee on Amount of Substance (CCQM). The CCQM has been active since 1993. It is the committee, established by the Comite International des Poids et Mesures, which is responsible for issues regarding metrology in chemistry. It has four established working groups in the fields of organic analysis, inorganic analysis, gas analysis and electrochemical analysis. A further twoad hoc working groups in the fields of surface analysis and metrology in biotechnology were established during the meeting. The working groups are involved in the identification, development and execution of a series of key comparisons, which will establish the technical basis for the mutual recognition of measurement capabilities among the National Measurement Institutes. 17 key comparisons are currently planned for the period 1999–2002, with 29 other international comparisons planned for the same period.