The comparison required the assignment of the mass fraction of folic acid present as the main component in the comparison sample. Performance in the comparison is representative of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molecular weight range 300–500] and high polarity (pKOW < −2). Methods used by the eighteen participating NMIs or DIs were based on a mass balance (summation of impurities) or qNMR approach, or the combination of data obtained using both methods. The qNMR results tended to give slightly lower values for the content of folic acid, albeit with larger associated uncertainties, compared with the results obtained by mass balance procedures. Possible reasons for this divergence are discussed in the report, without reaching a definitive conclusion as to their origin. The comparison demonstrates that for a structurally complex polar organic compound containing a high water content and presenting a number of additional analytical challenges, the assignment of the mass fraction content property value of the main component can reasonably be achieved with an associated relative standard uncertainty in the assigned value of 0.5% 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 CCQM Organic Analysis Working Group (OAWG) agreed on a Track A comparison for the measurement of polar organic in biological matrix as part of its 10-year strategic plan. As a model for this comparison, two polar clinical biomarkers: urea and uric acid, in human serum were chosen. This comparison was designed to enable participating National Metrology Institutes (NMIs) or Designated Institutes (DIs) to demonstrate their measurement capabilities in the determination of analytes with molecular mass of 50 to 500 g/mol, having the polarity pKOW > 2 in the range of 10 to 2,000 mg/kg in a biological matrix such as human serum, blood and urine. Two pools of human serum materials with different concentration levels of urea and uric acid were used as the comparison materials. Fifteen NMIs/DIs participated in this Track A comparison. All of them submitted the results for urea and 14 NMIs/DIs submitted the results for uric acid. With the exception of one NMI, all participating institutes employed isotope dilution mass spectrometry (IDMS) for the measurement of both urea and uric acid. Protein precipitation, liquid-liquid extraction and/or clean-up were applied, followed by instrumental analyses using GC-HRMS, GC-MS/MS, GC-MS, LC-HRMS, LC-MS/MS, LC-MS or HPLC-DAD. The Laplacian weighted medians were used as the Key Comparison Reference Values (KCRVs). The assigned KCRVs were the weighted medians of 13 results for urea (both serum pools), 10 results for uric acid (Serum I) and 11 results for uric acid (Serum II). Urea (Serum I) was assigned a KCRV of 1,486.0 mg/kg with a standard uncertainty of 9.0 mg/kg, urea (Serum II) was assigned a KCRV of 334.7 mg/kg with a standard uncertainty of 1.8 mg/kg, uric acid (Serum I) was assigned a KCRV of 136.50 mg/kg with a standard uncertainty of 0.98 mg/kg, and uric acid (Serum II) was assigned a KCRV of 39.39 mg/kg with a standard uncertainty of 0.11 mg/kg. The degree of equivalence (with the KCRV) and its uncertainty were calculated for each result. The majority of the participating institutes in CCQM-K109 demonstrated their capabilities in the measurement of the clinical markers in the biological matrix using IDMS. KEY WORDS FOR SEARCH Clinical biomarkers; urea; uric acid; human serum, IDMS 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).

ResumenMediante un proyecto de colaboración, se llevaron a cabo estudios de comparación para mejorar la capacidad de medición de los laboratorios participantes, apoyándolos en la producción, caracterización y distribución de materiales de referencia del sector agroalimentario. El proyecto fue planteado en cuatro etapas anuales (leche, agua, carne y granos). La tercera etapa en específico tuvo el objetivo de cuantificar y certificar el contenido de los parámetros nutrimentales (nitrógeno, grasa, sodio y potasio) de un lote candidato a Material de Referencia Certificado (MRC) de carne bovina enlatada. Dicho estudio fue realizado en colaboración entre varios Institutos Nacionales de Metrología (INM) y/o laboratorios colaboradores, los cuales, una vez que identificaron las posibles causas de variabilidad o de sesgo en las mediciones, así como las oportunidades de mejora, lograron la certificación del material de carne bovina. El MRC fue distribuido entre los participantes para cubrir las necesidades de la industria alimentaria de productos cárnicos y laboratorios de prueba de sus respectivos países. Palabras clave: Material de referencia, Material de Referencia Certificado, trazabilidad, incertidumbre.

The 2017 CCQM-K147 "Comparison of value-assigned CRMs for niacin (vitamin B3) in milk powder and infant formula matrices" is the first Key Comparison directly testing the chemical measurement services provided to customers by National Metrology Institutes (NMIs) and Designated Institutes (DIs) through certified reference materials (CRMs). CRMs certified for vitamin B3 (as niacin or niacinamide) content in milk powder and infant formula matrices were compared using measurements made on these materials under repeatability conditions. Five NMIs/DIs submitted seven CRMs certified for niacinamide and two CRMs certified for niacin. These materials represent most of the higher-order reference materials available in 2017 for this important nutrimental measurand. Generalized Gauss Markov Regression (GGMR) and Bayesian methods were used to establish the Key Comparison Reference Function (KCRF) relating the CRM certified values to the repeatability measurements. The niacinamide and niacin results for all nine CRMs were deemed equivalent at the 95 % level of confidence and were used to define the KCRF for vitamin B3 (as niacinamide). Monte Carlo methods and Bayesian methods were used to estimate 95 % level-of-confidence coverage intervals for the relative degrees of equivalence of materials, %d ± U95 (%d), and of the participating NMIs/DIs, %D ± U95 (%D). The Bayesian method estimates were selected as the final DoE values. For the niacinamide and niacin materials, all of the %D ± U95(%D) intervals, were within (-10 to 10) % of the consensus results and all of these are statistically equivalent. These results demonstrate that the participating institutions can value-assign CRMs for niacinamide and/or niacin in milk powder and infant formula matrices. KEY WORDS FOR SEARCH Niacin, Niacinamide, milk, infant formula, CRMs 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 CCQM OAWG 2017 CCQM-K142 "Comparison of CRMs and Value-Assigned Quality Controls: Urea and Uric Acid in Human Serum or Plasma" is the third Model 2 Key Comparison coordinated by the OAWG directly testing the chemical measurement services provided to customers by National Metrology Institutes (NMIs) and Designated Institutes (DIs) through certified reference materials (CRMs). CRMs certified for urea and/or uric acid content in human serum or plasma were compared using measurements made on these materials under repeatability conditions. Four NMIs/DIs submitted 10 CRMs certified for urea; five NMIs/DIs submitted 12 CRMs certified for uric acid. These materials represent most of the higher-order reference materials available then for these clinically important measurands. Uncertainty-weighted generalised distance regression was used to establish the Key Comparison Reference Function (KCRF) relating the CRM certified values to the repeatability measurements. The urea results for all 10 CRMs were considered to be equivalent at the 95 % level of confidence and were used to define the KCRF for urea. The uric acid result for one of the 12 CRMs was found to be non-equivalent: the submitting NMI re-evaluated the result and withdrew the material from use in defining the KCRF for uric acid. The remaining 11 CRMs were used to define the KCRF for uric acid. Monte Carlo methods were used to estimate 95 % level-of-confidence coverage intervals for the relative degrees of equivalence of materials, %d ± U95 (%d), and of the participating NMIs/DIs, %D ± U95 (%D). For the urea materials, the %D ± U95(%D) intervals were within (-3 to 5) % of the consensus results. For the uric acid materials from four of the five NMIs/DIs, the %D ± U95(%D) intervals were within (-4 to 5) % of the consensus results. These results demonstrated that with the exception of one material, the participating institutions could value-assign CRMs for urea and/or uric acid in human serum and plasma. KEY WORDS FOR SEARCH Certified reference materials; urea; uric acid; human serum; key comparison reference function 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).