Certification of trace and major elements and methylmercury concentrations in a macroalgae (Fucus sp.) reference material, IAEA-140

A marine reference material, IAEA-140, prepared with a macroalgae (Fucus sp.) was recently produced by the International Atomic Energy Agency and certified for trace and major elements and for methylmercury (MeHg). Certification of this material was achieved as an outcome of an international analytical intercomparison study which resulted in 116 independent sets of results reported by participants from 54 countries. The statistical evaluation of the collected data and the criteria used for assignment of the mean and uncertainty values are described. The analysis of data allowed to certify concentration values for 24 elements and MeHg, and to provide information values for another 10 elements. Regarding the elements which could be given certified values, between two and eight different instrumental methods were used to measure metal concentrations, and four independent analytical procedures were used to measure MeHg concentrations. In order to assess the results of the certification procedure, a comparison was made between the certified values obtained from the world-wide intercomparison results and the values obtained from a small subgroup of well-qualified laboratories. The means and 95% confidence intervals for reference values obtained by the two methods are similar for most elements showing that the usual method of certification used by the IAEA, based on large groups of participants, is indeed pertinent.     

Certification for trace elements and methyl mercury mass fractions in IAEA-452 scallop (Pecten Maximus) sample

A marine certified reference material (CRM), IAEA-452, prepared with scallop (Pecten maximus) sample was recently produced by the International Atomic Energy Agency (IAEA) and certified for trace elements and methyl mercury (MeHg). The Scallop (Pecten maximus) sample is commonly found and consumed seafood and is also used as bio-indicators for trace metal contamination in marine pollution studies. This paper presents the sample preparation methodology, material homogeneity and stability studies, evaluation of certification campaign results, the assignment of property values and their associated uncertainty. The reference values and associated expanded uncertainty for 9 trace elements (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb and Zn) and MeHg in scallop sample are established. The informative value for one more element (Ni) is also given. The new CRM can be used for the development and validation of analytical methods for determination of trace elements and methyl mercury in seafood and also for quality assurance/quality control purposes.     

Interlaboratory study to improve the quality of trace element determinations in rainwater

This is the first publication which describes the development of a reference material (RM) for the determination of 11 trace elements (Cu, Pb, Mn, Ni, Zn, Fe, Cd, Co, V, As and Al) in rainwater at microgram per liter concentrations. An interlaboratory comparison study for the determination of trace elements in rainwater was carried out for material performance studies to establish analyte concentrations with a stated uncertainty. Fifteen reputed laboratories from Asia, Europe and North America participated in the study. These laboratories used their regular in-house methods to analyze the rainwater samples. The aim of this study is to establish concentration levels of trace elements in rainwater based on interlaboratory study results. Details of the production, homogeneity and stability of the reference sample are given in this article. The organization of the study and the quality assurance measures undertaken at the organizer's laboratory are described. The analytical results obtained from individual laboratories and the analytical methods used for the determination of trace elements in rainwater are discussed. Based on the results obtained from the intercomparison study, certified values as well as informative values are assigned to the 11 trace elements in rainwater.     

New NIST sediment SRM for inorganic analysis

NIST maintains a portfolio of more than 1300 standard reference materials (SRM), more than a third of these relating to measurements in the biological and environmental fields. As part of the continuous renewal and replacement efforts, a set of new marine sediments has been recently developed covering organic and inorganic determinations. This paper describes the steps taken in sample preparation, homogeneity assay, and analytical characterization and certification with specific emphasis on SRM 2702 inorganics in marine sediment. Neutron activation analysis showed the SRM to be highly homogeneous, opening the possibility for use with solid sampling techniques. The certificate provides certified mass fraction values for 25 elements, reference values for eight elements, and information values for 11 elements, covering most of the priority pollutants with small uncertainties of only several percent relative. The values were obtained by combining results from different laboratories and techniques using a Bayesian statistical model. An intercomparison carried out in field laboratories with the material before certification illustrates a high commutability of this SRM.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Interlaboratory comparison of actinides in human tissue239Pu and240Pu

An international laboratory intercomparison of actinides in human tissues was organized by the United States Transuranium Registry and the National Institute of Standards and Technology. Five laboratories from the United States, United Kingdom, and Japan participated in the intercomparison. The laboratories were requested to analyze Standard Reference Materials 4351 (Human Lung) and 4352 (Human Liver) for²³⁹Pu and²⁴⁰Pu concentration. Approximately equivalent measurement capabilities were generally found among the participants. The results of this intercomparison were statistically comparable to those used for the original certification of the SRM's and were combined for a re-evaluation of the certified values. The combined data sets provide a better characterization of the inhomogeneity of these reference materials and result in a better basis for certification.Deceased.     

Results of the ASTM Nuclear Methods intercomparison on NIST apple and peack leaves standard reference materials

The ASTM Task Group on Nuclear Methods of Chemical Analysis (E10.05.12) has conducted a trace element intercomparison among some of its members over the past two years. Eight non-NIST laboratories submitted data using nuclear techniques, with a total of 111 values for the apple leaves and 116 values for the peach leaves, on 46 and 50 elements, respectively. This intercomparison provided a unique opportunity for the analytical laboratories, because the analytical values submitted could be later compared to the NIST certified values. For the seven elements which were certified by NIST and had three or more intercomparison values, the results showed that: 1) 61% of all 56 intercomparison values submitted had results whose stated uncertainty overlapped the uncertainty limits of the NIST certified values, and 2) less than 6% of the intercomparison values had means which fell outside ±20% of the NIST values. In general, the intercomparison values submitted showed excellent agreement with the NIST values. However, many reported uncertainties accompanying intercomparison values appeared overly optimistic.     

Use of an excess variance approach for the certification of reference materials by interlaboratory comparison

In the nuclear field, the accuracy and comparability of analytical results are crucial to insure correct accountancy, good process control and safe operational conditions. All of these require reliable measurements based on reference materials whose certified values must be obtained by robust metrological approaches according to the requirements of ISO guides 34 and 35. The data processing of the characterization step is one of the key steps of a reference material production process. Among several methods, the use of interlaboratory comparison results for reference material certification is very common. The DerSimonian and Laird excess variance approach, described and implemented in this paper, is a simple and efficient method for the data processing of interlaboratory comparison results for reference material certification. By taking into account not only the laboratory uncertainties but also the spread of the individual results into the calculation of the weighted mean, this approach minimizes the risk to get biased certified values in the case where one or several laboratories either underestimate their measurement uncertainties or do not identify all measurement biases. This statistical method has been applied to a new CETAMA plutonium reference material certified by interlaboratory comparison and has been compared to the classical weighted mean approach described in ISO Guide 35. This paper shows the benefits of using an “excess variance” approach for the certification of reference material by interlaboratory comparison.     

Characterization of a wheat flour reference material (ARC/CL) for twelve elements

Summary An ARC/CL coded wheat flour reference material (ARC/CL RM) with established recommended concentration values for 12 elements [1,2] was further characterized for P, K and Cr contents by means of an intercomparison study. Minor corrections were made to earlier recommended values in accordance with new results obtained. Fifteen laboratories using a total of 11 methods based on six entirely different analytical principles participated in the intercomparison study. The medians and standard deviations were calculated for the results of the intercomparison study. After rejecting as outliers values falling outside the median ± sd, the present recommended values were obtained by recalculating the median and 95% confidence limits. Recommended values were established for the major elements Ca, K, Mg, P, the minor elements Cu, Fe, Mn, Zn, and the trace elements Mo, Cr, Ni and Se. The relative standard deviations for the 95% confidence limits of the medians were lower than 10% for major and minor elements, 11% for Mo and 18% for Cr. All of the recommended concentration values fell into category A, having a high degree of confidence. The present RM, with its 16 recommended concentrations, is of value for use in nutritional, food composition and contaminant monitoring studies.     

Preparation of the bovine liver 12-02-01 reference material and the certification of element contents from an interlaboratory comparison

Summary The preparation of the bovine liver 12-02-01 reference material, its stabilization and homogeneity testing is presented. Evaluation of an interlaboratory comparison in which 31 laboratories took part using several analytical methods is described. From the results of the intercomparison, the contents of the elements Cd, Cu, Hg, Mn, Pb, Se, and Zn were certified, while for the elements Br, Co, Fe, K, Mo, Na, and Rb, information values were derived. Non-recommended values for the elements Ag, As, Ca, Cl, Cr, Cs, La, Mg, S, Sb, Sn, Sr, and V were also evaluated.Denoted as CZIM-liver in the report [23]     

Standard reference materials (SRMs) for determination of organic contaminants in environmental samples

For the past 25 years the National Institute of Standards and Technology (NIST) has developed certified reference materials (CRMs), known as standard reference materials (SRMs), for determination of organic contaminants in environmental matrices. Assignment of certified concentrations has usually been based on combining results from two or more independent analytical methods. The first-generation environmental-matrix SRMs were issued with certified concentrations for a limited number (5 to 10) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Improvements in the analytical certification approach significantly expanded the number and classes of contaminants determined. Environmental-matrix SRMs currently available include air and diesel particulate matter, coal tar, marine and river sediment, mussel tissue, fish oil and tissue, and human serum, with concentrations typically assigned for 50 to 90 organic contaminants, for example PAHs, nitro-substituted PAHs, PCBs, chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs). Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Certification of methylmercury in cod fish tissue certified reference material by species-specific isotope dilution mass spectrometric analysis

A new cod fish tissue certified reference material, NMIJ CRM 7402-a, for methylmercury analysis was certified by the National Metrological Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Cod fish was collected from the sea close to Japan. The cod muscle was powdered by freeze-pulverization and was placed into 600 glass bottles (10 g each), which were sterilized with γ-ray irradiation. The certification was carried out using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), where ²⁰²Hg-enriched methylmercury (MeHg) was used as the spike compound. In order to avoid any possible analytical biases caused by nonquantitative extraction, degradation and/or formation of MeHg in sample preparations, two different extraction methods (KOH/methanol and HCl/methanol extractions) were performed, and one of these extraction methods utilized two different derivatization methods (ethylation and phenylation). A double ID method was adopted to minimize the uncertainty arising from the analyses. In order to ensure not only the reliability of the analytical results but also traceability to SI units, the standard solution of MeHg used for the reverse-ID was prepared from high-purity MeHg chloride and was carefully assayed as follows: the total mercury was determined by ID–ICPMS following aqua regia digestion, and the ratio of Hg as MeHg to the total Hg content was estimated by GC–ICPMS. The certified value given for MeHg is 0.58 ± 0.02 mg kg⁻¹ as Hg. Figure NMIJ CRM 7402-a: cod fish tissue for MeHg analysis     

Some difficult problems still existing in the preparation and certification of CRMs

Differences between particle size measurements of CRMs by various methods are discussed and the importance of the reliability of such data for proper estimation of the homogeneity of the material is emphasized. On the basis of a very simple model, the dependence of the Ingamells' sampling constant on the average mass of a single particle of the material is derived, and theoretical predictions are compared with the experimental results. Various approaches to the certification of the candidate RMs are briefly reviewed. The merits of the approach being used in this laboratory to evaluate data obtained in the interlaboratory comparison, and to assign certified and information values, is discussed. The conclusions are supported by results obtained for selected trace elements by use of "definitive" (primary) and "very accurate" methods. Some observations on the unusual resistance of some biological materials to wet ashing and the resulting possibility of making analytical errors are mentioned.     

Adsorption of cobalt on some natural zeolites occurring in ČSFR

Neutron activation analysis is one of many analytical techniques used at the National Institute of Standards and Technology (NIST) for the certification of NIST Standard Reference Materials (SRMs). NAA competes favorably with all other techniques because of it's unique capabilities for high accuracy even at very low concentrations for many elements. In this paper, instrumental and radiochemical NAA results are described for 25 elements in two new NIST SRMs, SRM 1515 (Apple Leaves) and SRM 1547 (Peach Leaves), and are compared to the certified values for 19 elements in these two new botanical reference materials.     

Feasibility study for the production of certified calibrants for the determination of deoxynivalenol and other B-trichothecenes: intercomparison study

Thirteen European laboratories experienced in the analysis of mycotoxins participated in an intercomparison study within a European Commission-funded project. Goals of the study were to check the fitness for purpose of a small batch of gravimetrically prepared calibrants; to compare individually prepared calibrants with common calibrants; to check the feasibility of toxin mixtures as calibrant solutions; and to give recommendations on the production of future certified reference materials (CRMs) with regard to the nature of the calibrant and the means of certification. Each laboratory received ampules of each common calibrant containing single toxins [solution containing either deoxynivalenol (DON), 3-acetyl-DON (3-Ac-DON), nivalenol (NIV), or 15-acetyl-DON (15-Ac-DON)] and 3 ampules of toxin-mixture (solutions of DON + 3-Ac-DON + NIV in acetonitrile) of known concentrations (about 20 microg/mL). Ampules with single toxins (solution containing either DON, 3-Ac-DON, NIV, or 15-Ac-DON) and a toxin-mixture (solutions of DON + 3-Ac-DON + NIV in acetonitrile) of unknown concentrations were distributed to the participants for quantification. The participating laboratories used mainly high-performance liquid chromatography (HPLC)-diode array detection UV for DON, 3-Ac-DON, NIV, and 15-Ac-DON; gas chromatography-electron capture detection (GC-ECD) and GC-mass spectrometry methods were used sparingly. Linear calibration curves were achieved by >90% of the participants. Relative between-day variation (RSDr) of 26% of the laboratories was greater than the target value of 5% for HPLC, and RSDr of 32% of the laboratories was greater than the desired value of 10% for GC. Relative between-laboratory variation (RSDR) of the GC results obtained with single common calibrants was greater than the target value of 16% for all laboratories. RSDR of the HPLC results for the common unknown single toxin solutions was less than the target value of 8% except for 15-Ac-DON. Generally, better recoveries were observed from common calibrants (102% for mix calibrants and 98% for single calibrants) than from individually prepared calibrants (95%). This international comparison study clearly showed the high scattering of results in the analysis of type-B trichothecenes, particularly when GC was used. Obviously, this intercomparison study was not suited for the certification of B-trichothecenes. A certification of the proposed calibrant material was therefore recommended on the basis of its gravimetrical preparation.     

Certifying the chemical composition of a biological material — a case study

A worldwide laboratory intercomparison was organized by the International Atomic Energy Agency's Analytical Quality Control Services (AQCS) involving the determination of trace elements in plant materials used for human consumption. The National Institute of Standard and Technology (NIST) Standard Reference Materials Program donated 5 kg of spinach designated for the production of the future Standard Reference Material SRM 1570a to this intercomparison; the AQCS provided a similar amount of cabbage. For the study, 150 units of each material were distributed and 114 laboratories reported results on both materials to AQCS. The results for the spinach, encompassing more than forty elements, have been compiled and evaluated; estimates of the elemental concentrations were made based on statistical evaluations, principles of analytical procedures and the laboratory performance indicated by the results on the cabbage material. Satisfactory estimates were obtained for 27 elements. Comparison with IAEA laboratory and NIST reference data did not reveal any significant bias that might have been introduced by the intercomparison approach or its evaluation.     

Certification of a new NIST fly ash standard reference material

In June 1993 the National Institute of Standards and Technology (NIST) released the third version of Constituent Elements in Coal Fly Ash Standard Reference Material (SRM 1633b). This material is intended for quality assurance purposes in evaluating the analytical methods used for the determination of constituent elements in coal fly ash or in materials with similar matrices. It has been certified for 23 major, minor and trace elements using ten different analytical techniques. For an element to be certified in a NIST SRM, its concentration is usually determined by at least two independent analytical techniques. The concentrations of additional 24 elements are provided for information only purposes in the new fly ash. Current plans are to certify the concentrations of a number of rare earths upon completion of additional analytical work now in progress. Homogeneity testing was accomplished using instrumental neutron activation analysis and X-ray fluorescence. This presentation summarizes the preparation of this new material and the analytical results used for certification.     

Some difficult problems still existing in the preparation and certification of CRMs

Differences between particle size measurements of CRMs by various methods are discussed and the importance of the reliability of such data for proper estimation of the homogeneity of the material is emphasized. On the basis of a very simple model, the dependence of the Ingamells’ sampling constant on the average mass of a single particle of the material is derived, and theoretical predictions are compared with the experimental results. Various approaches to the certification of the candidate RMs are briefly reviewed. The merits of the approach being used in this laboratory to evaluate data obtained in the interlaboratory comparison, and to assign certified and information values, is discussed. The conclusions are supported by results obtained for selected trace elements by use of “definitive” (primary) and “very accurate” methods. Some observations on the unusual resistance of some biological materials to wet ashing and the resulting possibility of making analytical errors are mentioned.