Development and validation of a methodology for uranium radiochronometry reference material preparation

The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the ²³⁰Th/²³⁴U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a ²³²Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide ²³⁰Th and the measured ²³⁰Th/²³⁴U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation.     

Feasibility study for the preparation of certified reference materials part I – mineral oil contaminated soils

The international joint project HYCREF (Contract No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogeneous and stable reference materials of water, soil, and waste contaminated with mineral oil hydrocarbons and to certify the mineral oil content by gas chromatographic methods. The results of a feasibility study for the preparation of three soil reference materials are discussed in this paper, and for the preparation of three waste reference materials in the second part (Koch et al., Accred Qual Assur submitted for publication). The soil materials were selected to represent different soil types and contamination levels. The project plan set three requirements for these reference materials: uncertainty in the mineral oil content resulting from the certification exercise <5%, a sample inhomogeneity of <3% and a minimum long-term stability of 5 years. For the most part, these requirements were met within this project.     

Availability of reference materials: COMAR the database for certified reference materials

COMAR is the international database for certified reference materials. A new user-friendly web-based version, COMAR², has been developed by BAM and CONET Consulting AG which will be available in December 2002. The advantages of COMAR² are briefly explained.Presented at the International ILAC/IAF Conference on Accreditation in Global Trade, 23-25 September 2002, Berlin, Germany     

A mussel tissue certified reference material for multiple phycotoxins. Part 1: design and preparation

The development of multi-analyte methods for lipophilic shellfish toxins based on liquid chromatography–mass spectrometry permits rapid screening and analysis of samples for a wide variety of toxins in a single run. Validated methods and appropriate certified reference materials (CRMs) are required to ensure accuracy of results. CRMs are essential for accurate instrument calibration, for assessing the complete analytical method from sample extraction to data analysis and for verifying trueness. However, CRMs have hitherto only been available for single toxin groups. Production of a CRM containing six major toxin groups was achieved through an international collaboration. Preparation of this material, CRM-FDMT1, drew on information from earlier studies as well as improved methods for isolation of toxins, handling bulk tissues and production of reference materials. Previous investigations of stabilisation techniques indicated freeze-drying to be a suitable procedure for preparation of shellfish toxin reference materials and applicable to a wide range of toxins. CRM-FDMT1 was initially prepared as a bulk wet tissue homogenate containing domoic acid, okadaic acid, dinophysistoxins, azaspiracids, pectenotoxin-2, yessotoxin and 13-desmethylspirolide C. The homogenate was then freeze-dried, milled and bottled in aliquots suitable for distribution and analysis. The moisture content and particle size distribution were measured, and determined to be appropriate. A preliminary toxin analysis of the final material showed a comprehensive toxin profile.     

Accreditation and the need for certified reference materials

The comparability of data from accredited laboratories is not always as good as customers would desire. A number of reasons for this fact are given. Clients of laboratories do not specify methodology, which may lead to the application of systematically different methods or to methodology with improper performance characteristics. Laboratories do not always validate methodology sufficiently which is, however, among others provoked by a lack of reference materials. It is argued that accreditation cannot enforce comparability on itself, but needs to be embedded in a measurement infrastructure. The quality systems which underly accreditation form a basic element. In addition, adequate methods, good laboratory performance studies and certified reference materials are required.     

Update on COMAR: the Internet database for certified reference materials

This paper describes the COMAR database for certified reference materials (CRMs). The Web-based version of COMAR is freely accessible via the Internet. COMAR was established to assist laboratories in finding the CRMs needed. The database is maintained in a collaboration of the world’s major CRM producers. The planned changes in the database as agreed at the last COMAR council meeting in Prague in May 2006 are indicated.

Trends in certified reference materials for the speciation of trace elements.

The measurement of the chemical species of elements (instead of the total element concentration) has become an irreversible trend in analytical chemistry. The motivation lies in the fact that the biochemical and geochemical behaviour of an element is governed by its species. Quality assurance of the analytical procedures used for speciation analysis requires the analysis of representative reference materials, certified for the relevant species. Up to now the number of existing certified reference materials for trace element species is very limited. The most important ones are environmental CRMs certified for trialkyltin compounds, methylmercury, Cr(III)/Cr(VI) and food CRMs certified for arsenic species and methylmercury. Major developments are to be expected in CRMs focussed on environmental problems, including waste treatment, on bioavailability of trace elements in food and on bio-monitoring in occupational health and hygiene. It is, however, unlikely that the producers of CRMs will ever be able to cover all needs. Add to this that many, very active species are notoriously unstable and/or short living and require in-situ analysis. This will lead to different analytical developments, such as analyses in-situ, where the classical concept of CRMs may not stand firm anymore.     

Feasibility studies for the preparation and certification of reference materials Part II: mineral oil contaminated waste materials

The 2-year international joint project HYCREF (Contract-No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogenous and stable water-, soil- and waste reference materials contaminated with mineral oil hydrocarbons and to test certify the mineral oil content by gas chromatographic methods. As mineral oil products are important sources for environmental contaminations, appropriate reference materials certified by using the new gas chromatographic methods (soil: ISO/FDIS 16703, waste: prEN 14039 and KW/04, water: ISO 9377-2) are highly needed. Additional to the HYCREF-results presented in part I–mineral contaminated soils–this second paper gives an overview of the feasibility study for the preparation and test certification of three waste reference materials (offshore marine sediment, building material and industrial waste). The following specifications, which had been defined in the project work plan, were reached successfully: uncertainty of the mineral oil content resulting from the certification exercise ≤5% and a between-bottle inhomogeneity of ≤3%. All three materials have been evaluated for long- and short term stability. They contain different levels and types of mineral oil and cover the full application range of ISO/FDIS 16703 and prEN 14039 (100–10,000 mg/kg). The expanded uncertainties U _cert of the three materials are about 6%. In this way, they are comparable to ERM^®-CC015a (U _cert=7.1%, mineral oil in a river sediment) and are suited to close the present gap of commercially available CRM for mineral oil determination in waste.     

IRMM-3100a: A new certified isotopic reference material with equal abundances of 233U, 235U, 236U and 238U

The new so-called Quad-IRM (“Quadruple Isotope Reference Material”) was prepared from highly enriched ²³³U, ²³⁵U, ²³⁶U and ²³⁸U isotopic materials using an optimized combination of gravimetrical mixing and mass spectrometry. Within the mixing process the isotope ratios were adjusted to about n(²³³U)/n(²³⁵U)/n(²³⁶U)/n(²³⁸U) = 1/1/1/1 and certified with expanded relative uncertainties of 0.0054% per mass unit (coverage factor k = 2). This new isotope reference material is ideal for verifying the inter-calibration of multi-detector systems in isotope mass spectrometry.The certified n(²³³U)/n(²³⁶U) ratio of IRMM-3100a was derived from the mass metrology data of the gravimetrical mixing of highly enriched ²³³U and ²³⁶U materials. It was verified by thermal ionization mass spectrometry (TIMS) measurements using the classical total evaporation (TE) and modified total evaporation (MTE) methods. The n(²³⁴U)/n(²³⁶U), n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were then determined by TIMS using the n(²³³U)/n(²³⁶U) ratio for internal normalization and using a multi-dynamic measurement procedure in order to circumvent any possible influence and uncertainties from Faraday cup efficiencies and amplifier gain factors. The certified n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were additionally verified using the classical and modified total evaporation methods using two TIMS instruments at IRMM and one TIMS instrument at IAEA-SGAS. The verification data can be regarded as results obtained at three independent instruments at two different nuclear safeguards laboratories.     

Certified reference materials to support a European thematic strategy for soil protection: the EUROSOILS (IRMM-443) experience

The recent proposal of thematic strategy for soil protection by the European Commission outlines that knowledge of problems associated with soil has increased considerably based on surveys, monitoring systems and data networks. Although this information is very useful, its value for the policy-making process is limited due to a lack of comparability. From this unsatisfying situation the need arises to develop an EU-wide monitoring system accompanied by suitable matrix reference materials. Experiences gained from the development and certification of IRMM-443 (The EUROSOILS) show how to approach the complex problem of providing suitable (i.e. representative) soil CRMs for the arising analytical needs to support existing and upcoming EU legislation.This paper presents briefly the quantitative findings of a certification exercise (adsorption coefficients for atrazine, lindane and 2,4-D, as well as pH in suspension). A comparison of these results with those of an intercomparison exercise organised in 1989 by the German UBA on very similar soils shows the significant improvement in the determination of soil adsorption coefficients that was induced by the EUROSOIL project. Indicative values of total and organic carbon content and nitrogen according to ISO Standards are also presented.Furthermore, the idea of reference soils and derived reference materials (for analytical purposes) as well as reference matrices (substrates for ecotoxicological testing) is highlighted and set into the context of horizontal standardisation of methods.     

A mussel tissue certified reference material for multiple phycotoxins. Part 3: homogeneity and stability

A candidate certified reference material (CRM) for multiple shellfish toxins (domoic acid, okadaic acid and dinophysistoxins, pectenotoxins, yessotoxin, azaspiracids and spirolides) has been prepared as a freeze-dried powder from mussel tissues (Mytilus edulis). Along with the certified values, the most important characteristics for a reference material to be fit-for-purpose are homogeneity and stability. Acceptable between-bottle homogeneity was found for this CRM. Within-bottle homogeneity was assessed using domoic acid, and it was shown that repeated subsampling of the CRM can be performed precisely down to 0.35 g. Both short- and long-term stability studies carried out under isochronous conditions demonstrated excellent stability of the various toxins present in the material. While degradation of some analytes was observed at +60°C in short-term studies, it was determined that shipping at ambient temperature is adequate. No instability was detected in long-term stability studies, and it was shown that the material can be held at +18°C safely for up to 1 year. To guarantee stability of the CRM over its lifetime the stock will be maintained at −20°C. The results of the homogeneity and stability testing show that CRM–FDMT1 is appropriate for its intended use in quality assurance and quality control of shellfish toxin analysis methods.     

Validation of a fluidized-bed extraction method for solid materials for the determination of PAHs and PCBs using certified reference materials

In recent years, the classical Soxhlet extraction of PAHs and PCBs from matrices such as soil, sediments, sludges and related matrices has been substituted by faster and less-solvent-consuming automated techniques. This paper describes the performance characteristics of fluidized-bed extraction (FBE), which has been compared to other approaches and been optimized using a quality control material.SI-traceable reference materials from the European Commission have been used to validate the developed method and establish an analytical protocol. Good correlations with Soxhlet extraction were observed and certified values of the CRMs used, could be confirmed in all cases.     

Use of INAA in the preparation of a set of soil reference materials with certified values of total element contents

A set of certified Reference Materials was prepared consisting of four natural agricultural soils with normal (n) and elevated (e) levels of element contents: CRM 7001 Light Sandy Soil (n), CRM 7002 Light Sandy Soil (e), CRM 7003 Silty Clay Loam (n), and CRM 7004 Loam (e). In these materials, certified and/or information values of the total contents of the elements As, Ba, Be, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V and Zn, and their fractions extractable by aqua regia, boiling and cold 2M nitric acid were derived from an interlaboratory comparison in which 28 laboratories participated. Highly precise and accurate procedures of instrumental neutron activation analysis (INAA) were employed for homogeneity testing and also for certification of the total element contents. For comparation purposes, NIST SRM-2704 Buffalo River Sediment was analyzed by INAA, as well. The INAA results obtained compared very well with the certified and/or information values for four soil CRMs and also with NIST values for SRM-2704. From this agreement, a very high reliability of the new soil CRMs can be inferred.     

The urgent requirement for new radioanalytical certified reference materials for nuclear safeguards, forensics, and consequence management

A multi-agency workshop was held from 25 to 27 August 2009, at the National Institute of Standards and Technology (NIST), to identify and prioritize the development of radioanalytical Certified Reference Materials (CRMs, generally provided by National Metrology Institutes; Standard Reference Materials, a CRM issued by NIST) for field and laboratory nuclear measurement methods to be used to assess the consequences of a domestic or international nuclear event. Without these CRMs, policy makers concerned with detecting proliferation and trafficking of nuclear materials, attribution and retribution following a nuclear event, and public health consequences of a nuclear event would have difficulty making decisions based on analytical data that would stand up to scientific, public, and judicial scrutiny. The workshop concentrated on three areas: post-incident Improvised Nuclear Device (IND) nuclear forensics, safeguard materials characterization, and consequence management for an IND or a Radiological Dispersion Device detonation scenario. The workshop identified specific CRM requirements to fulfill the needs for these three measurement communities. Of highest priority are: (1) isotope dilution mass spectrometry standards, specifically ²³³U, ^236gNp, ²⁴⁴Pu, and ²⁴³Am, used for quantitative analysis of the respective elements that are in critically short supply and in urgent need of replenishment and certification; (2) CRMs that are urgently needed for post-detonation debris analysis of actinides and fission fragments, and (3) CRMs used for destructive and nondestructive analyses for safeguards measurements, and radioisotopes of interest in environmental matrices.     

A pilot study for the production of a certified reference material for trace elements in honey

In the context of the general mandate of the European Union Community Reference Laboratory (CRL) for residues in living animals and their products established at the Istituto Superiore di Sanità, a pilot study was undertaken to assess the possibility of producing a new certified reference material (CRM) for trace elements in a matrix of honey. The elements considered were As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sn, V and Zn. Their determination was performed by inductively coupled plasma (ICP)-based techniques. Data obtained with different ICP techniques were generally in good agreement. In light of these results, the next step was the effective production of a candidate CRM in a honey matrix. In the preliminary phase, two different types of honey, i.e., Eucalyptus (solid and sticky) and Robinia (viscous and sticky), were pretreated at the Institute for Reference Materials and Measurements, Joint Research Centre, European Commission (EC-JRC-IRMM) in order to produce the materials candidate for the certification process. Approximately 600 ampoules were thus produced for the Robinia honey and 450 ampoules for the Eucalyptus honey, each ampoule containing 5 g of an aqueous solution of honey (with 20% and 30% high purity water, respectively) and sealed under inert gas (Ar). A ring test to determine the levels of the chemical elements and a long-term study to evaluate the stability of the samples is in progress. Tentative figures for the analytes of interest are (in ng g⁻¹): Robinia, As, 1.28±0.09; Cd, 0.59±0.08; Cr, 2.36±0.21; Cu, 57.6±3.2; Fe, 209±9; Mn, 90.8±3; Ni, 18.1±0.6; Pb, 23±1.5; Sn, 8.10±0.35; V, 1.19±0.37; and Zn, 178±4; Eucalyptus, As, 3.18±0.21; Cd, 0.70±0.08; Cr, 2.73±0.22; Cu, 141±6; Fe, 926±16; Mn, 1905±81; Ni, 7.77±0.4; Pb, 138±4; Sn, 7.97±0.16; V, 3.47±0.15; and Zn, 405±9.     

Improvement of the traceability of reference materials certified for purity: evaluation of a semi-preparative high-performance liquid chromatography approach

A semi-preparative high-performance liquid chromatography process was evaluated as a tool to quantitatively determine the purity or percentage mass fraction content (% m/m) of organic compounds. The method is simple and does not require the identification and subsequent quantitation of organic-related structure impurities. A protocol was developed and tested on four reference materials certified for purity from 95% m/m to 99.3% m/m. Comparing the purity results of each certified reference material using the new approach with their respective certified values showed no significant analytical bias. Semi-preparative high-performance liquid chromatography has proved the potential to be a primary method directly traceable to mass with an uncertainty statement written down also in terms of mass with expanding uncertainty ranging from 0.8% to 1.3% m/m compared to 0.3 to 2.0% m/m for the certified purity values at the 95% confidence interval.