The quantitative characterisation of geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS)

The geology and mining industries rely heavily on reliable quantitative data on the elemental composition of various rocks and minerals. The analytical accuracy of the best measurement systems are, however, limited to the accuracy with which the composition of a generally accepted reference sample is known, which serves to calibrate an instrument or validate a method. Thus, there is an established market for well-characterised reference materials which trade internationally as value added commodities. International organisations prepare strict procedures for the preparation and certification of these reference materials. ISO/REMCO is the ISO Committee on Reference Materials that carries out and encourages a broad international effort for the harmonisation and promotion of reference materials, their production and their application. In view of recent developments in ISO/REMCO related to updated guides and changes in definitions, SARM 1 to 6 (the NIMROCs) are in danger of losing their status as certified reference materials (CRMs). Due to the continued popularity of the NIMROCs and the availability of bulk sample, the National Metrology Institute of South Africa (NMISA) embarked on a project to re-certify three materials from the suite of six igneous rock samples, i.e. SARM 2 (Syenite), SARM 3 (Lujavrite) and SARM 4 (Norite). The aim of the re-certification project was to re-certify the materials with a single primary reference measurement procedure in a single laboratory to comply with one of the possible routes to the establishment of metrological traceability as described in ISO Guide 34. Eight elements (Ba, Sr, Cd, Mo, Cu, Ni, Pb and Zn) of SARM 2, SARM 3 and SARM 4 were value assigned during this study to ensure that they comply with the ISO Guide 30 and ISO GUM requirements for traceability and measurement uncertainty. Traceability to the SI units of mass and amount of substance at the highest level of accuracy was established by employing the definitive technique of double isotope dilution ICP-MS, with primary assay standards traceable to the NIST SRM 3100 series and gravimetrically prepared samples. For the first time assigned values with uncertainty statements for these elements in these reference materials were calculated according to the ISO GUM and CITAC/EURACHEM guidelines for expression of the uncertainty of measurement. The uncertainties of the assigned values for all elements were within the target of 5% relative set during the development of the methodology, except for elements in concentrations below 10 mg.kg-1. The ID-ICP-MS results are supported by good comparability with results reported in the literature since 1978, as well as the original certified values published in 1978. The results from this study for all elements in these reference materials have the potential to become new certified values in accordance with the requirements of ISO Guides 34 and 35. This will improve the usefulness of these reference materials to the South African and international geology and mining communities for the purposes of analytical quality control and method validation in exploration and geochemical analysis. Confirmation of the homogeneity and stability of the remaining units of the reference materials is considered necessary to complete the re-certification project.Thesis (PhD)--University of Pretoria, 2010.Chemistryunrestricte

International comparison CCQM-K51: Carbon monoxide (CO) in nitrogen (5 µmol mol−1)

The first key comparison on carbon monoxide (CO) in nitrogen dates back to 1992 (CCQM-K1a). It was one of the first types of gas mixtures that were used in an international key comparison. Since then, numerous national metrology institutes (NMIs) have been setting up facilities for gas analysis, and have developed claims for their Calibration and Measurement Capabilities (CMCs) for these mixtures. Furthermore, in the April 2005 meeting of the CCQM (Consultative Committee for Amount of Substance) Gas Analysis Working Group, a policy was proposed to repeat key comparisons for stable mixtures every 10 years. This comparison was performed in line with the policy proposal and provided an opportunity for NMIs that could not participate in the previous comparison. NMISA from South Africa acted as the pilot laboratory. Of the 25 participating laboratories, 19 (76%) showed satisfactory degrees of equivalence to the gravimetric reference value. The results show that the CO concentration is not influenced by the measurement method used, and from this it may be concluded that the pure CO, used to prepare the gas mixtures, was not 13C-isotope depleted. This was confirmed by the isotope ratio analysis carried out by KRISS on a 1% mixture of CO in nitrogen, obtained from the NMISA. There is no indication of positive or negative bias in the gravimetric reference value, as the results from the different laboratories are evenly distributed on both sides of the key comparison reference value

Outline for the revision of ISO Guide 35

The production of reference materials (RMs) is a key activity for the improvement and maintenance of a worldwide coherent measurement system. As detailed in ISO Guide 33, RMs with different characteristics are used in measurements, such as calibration, quality control and method validation, as well as for the assignment of values to other materials. Currently, ISO Guide 35 is in its third edition after it was revised in 2006. The Guide was developed to support best practices in the value assignment to specified properties of Certified Reference Materials (CRMs). This Guide gives general guidance and explains concepts to assist the understanding and development of valid methods to assign values to the properties of a reference material, including the evaluation of their associated measurement uncertainties, and the establishment of their metrological traceability. From the outcome of a systematic review of ISO Guide 35 among the members of ISO/REMCO, the ISO Committee on Reference Materials, it followed that there is a need for revising the current edition of ISO Guide 35. The mandate for the revision is focused on editorial updates to explain the concepts in more detail. It is not envisaged that major technical changes will be introduced. This paper explains the approach and rationale for the revision of ISO Guide 35 and invites comments from the users of the current edition of ISO Guide 35.JRC.D.2-Standards for Innovation and sustainable Developmen

Development of a Method for the Determination of Total Selenium in Soil, Maize Plants, and Maize Flour by Inductively Coupled Plasma Tandem Mass Spectrometry (ICP-MS/MS)

Selenium (Se) is a micronutrient that has multiple biochemical effects ranging from a nutritional deficiency at low levels to toxicity at high levels. Its quantification in environmental systems is vital to protect the health of people and animals. This study developed and validated methods to determine the total selenium (Se) concentration in soil, maize plants, and maize flour. The performance of the methods was ascertained using matrix certified reference materials (CRMs), namely NMIJ CRM 7303-a (trace elements in lake sediments), NIST SRM 1646-a (estuarine sediments), NIST SRM 1570-a (spinach leaves), NIST SRM 1571 (orchard leaves), NCS ZC 73010 (maize flour) and NIST RM 8437 (hard red spring wheat flour). All methods fulfilled the performance requirements of the AOAC International. An acceptable accuracy was achieved with percentage recoveries between 57 and 102% and En-scores within ±1 limits. Repeatability (RSDr, %) and intermediate precision  (RSDR, %) ranged from 4 to 12%, and 9 to 15%, respectively. The limit of detection (LOD) and limit of quantification (LOQ) for soil were 0.024 ng. g−1 and 0.082 ng. g−1, respectively. The LODs and LOQs for maize plants and flour were 0.0036 and 0.0179 ng. g−1, respectively. The performance characteristics of the methods were comparable with previously reported methods, confirming reliability. The measurement uncertainty was evaluated following the guide to the expression of uncertainty in measurement (GUM). Relative expanded uncertainty at a 95% level of confidence (k=2) was less than 24% for the final measurement results for all the different matrices.</p

The new International Standard ISO 17034: general requirements for the competence of reference material producers

The International Organization for Standardization (ISO) has published ISO 17034:2016 on the minimum requirements for the competence of reference material producers. Previously these requirements were addressed in ISO Guide 34:2009, originally developed by the ISO Committee on Reference Materials (ISO/REMCO). The need for an International Standard was triggered as several accreditation bodies could not accredit to a guide, at all, while in other countries ISO Guide 34 could only serve as accreditation standard in combination with ISO/IEC 17025. For the transformation into a conformity assessment standard of the ISO/IEC 17000 series, the ISO Committee on Conformity assessment (ISO/CASCO) and ISO/REMCO joined their forces. A Joint Working Group, formed by experts and stakeholders from both committees, finalised the transformation within two years. During the transformation, the structure of ISO 17034 has been aligned with other ISO/IEC 17000 series standards and the content of ISO 17034 has been harmonised with the recent editions of other relevant ISO Guides. Requirements for the production of reference materials were elaborated on more clearly in the new standard, specifying the requirements for (non-certified) reference materials and the additional requirements for certified reference materials. The new International Standard ISO 17034:2016 supersedes ISO Guide 34:2009.JRC.F.6-Reference Material

Key comparison automotive gas mixtures

41 p. : il.The capabilities for the preparation of certified reference materials of carbon monoxide, carbon dioxide, and propane in nitrogen have been compared. The participating national metrology institutes submitted each a gravimetrically prepared gas mixture of a specified target composition typical for the automotive industry to the coordinating laboratory. All mixtures were analysed by the coordinating laboratory using a gas chromatograph equipped with a thermal conductivity detector in three runs under repeatability conditions. Based on the calibration curve, reference values were assigned to the amount fractions of carbon monoxide, carbon dioxide, and propane. The degrees–of- equivalence were established as difference between the gas composition as calculated from preparation and the measured one, and its associated uncertainty. All participants obtained satisfactory results