Environmental Reference Materials Research Articles

Dual-carbon isotope analysis of benzene polycarboxylic acids for tracking black carbon across different environments

Black carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (δ13C and Δ14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Δ14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure δ13C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-δ13C and BPCA-Δ14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired δ13C-Δ14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different δ13C-Δ14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages.

Establishing reference material for the quest towards standardization in environmental microbial metagenomic studies

Breakthroughs in DNA-based technologies, especially in metagenomic sequencing, have drastically enhanced researchers’ ability to explore environmental microbiome and the associated interplays within. However, as new methodologies are being actively developed for improvements in different aspects, metagenomic workflows become diversified and heterogeneous. Through a single-variable control approach, we quantified the microbial profiling variations arising from 6 common technical variables associated with metagenomic workflows for both simple and complex samples. The incurred variations were constantly the lowest in replicates of DNA isolation and DNA sequencing library construction. Different DNA extraction kits often caused the highest variation among all the tested variables. Additionally, sequencing run batch was an important source of variability for targeted platforms. As such, the development of an environmental reference material for complex environmental samples could be beneficial in benchmarking accrued non-biological variability within and between protocols and insuring reliable and reproducible sequencing outputs immediately upstream of bioinformatic analysis. To develop an environment reference material, sequencing of a well-homogenized environmental sample composed of activated sludge was performed using different pre-analytical assays in replications. In parallel, a certified mock community was processed and sequenced. Assays were ranked based on the reconstruction of the theoretical mock community profile. The reproducibility of the best-performing assay and the microbial profile of the reference material were further ascertained. We propose the adoption of our complex environmental reference material, which could reflect the degree of diversity in environmental microbiome studies, to facilitate accurate, reproducible, and comparable environmental metagenomics-based studies.

Geostandards and Geoanalytical Research Bibliographic Review 2021

This GGR Bibliographic Review is a survey of approximately 5200 geoanalytical publications for the year 2021. Selected articles, numbering over 340, containing measurement results for relevant geological and environmental reference materials are listed with individual summaries of target analytes, relevant reference materials and producers. A brief summary of a selection of these publications is included that highlights notable developments in geoanalytical studies, newly developed or characterised RMs, and new datasets of established reference materials that have been re‐analysed using improved or state‐of‐the‐art measurement techniques.

Cadmium Isotope Analysis Of Environmental Reference Materials Via Microwave Digestion–Resin Purification–Double-Spike MC-ICP-MS

Cadmium Isotope Analysis Of Environmental Reference Materials Via Microwave Digestion–Resin Purification–Double-Spike MC-ICP-MS

High-precision measurement of U-Pu-Np-Am concentrations and isotope ratios in environmental reference materials by mass spectrometry

We report results of precise and sensitive mass spectrometric measurements of uranium, plutonium, neptunium, and americium concentrations and isotope ratios in a variety of environmental reference materials. Most of our work has been done on NIST SRM 4350b, River Sediment, but we also present results for NIST SRM 4354, Lake Sediment; NIST SRMs 4355 and 4355a, Peruvian Soil; NIST SRM 4357, Ocean Sediment; NIST SRM 1648a, Urban Particulate Material; NIST SRM 1649b, Urban Dust; IAEA CRM 385, Ocean Sediment; USGS BCR-2, Columbia River Basalt; and USGS BHVO-2, Hawaiian Volcanic Observatory Basalt. These materials reflect a wide range in long-lived actinide concentrations (e.g. 1E4 to 1E10 atoms 239Pu/g) and isotope ratios. Measurements were performed in a clean laboratory by isotope dilution, multi-collector thermal ionization and multi-collector inductively coupled plasma mass spectrometry. In general, our results are in agreement with, but lower the uncertainty of, literature or certificate values for these reference materials. Our uranium results for the basalts also confirm previously reported high-precision mass spectrometric results from our laboratory. In many cases our measurements of U-Pu-Np-Am nuclides appear to be novel.Extensive results for NIST SRM 4350b, River Sediment, indicate that this material is heterogeneous for Pu-Np-Am concentrations and isotope ratios at a sample size of 5 g or lower. Pu–Np isotope ratios and a241Pu-241Am model age of 1954 reflect a mix of plutonium production operations at the nearby Hanford, Washington site, and global atmospheric fallout from nuclear weapons testing. Results for the oceanic sediment materials (NIST SRM 4357 and IAEA 385) collected near Sellafield, U.K. vary but are also indicative of local anthropogenic sources of varying Pu isotopic composition and a mean 241Pu-241Am model age of 1964. Large environmental fractionation between Pu and Np is observed for the ocean, river, and lake sediment reference materials. Novel measurements for the two air particulate SRMs indicate high U, Pu and Np concentrations for these collections in 1976–1977 with an anomalous regional fallout Pu isotopic signature. Results for BHVO-2 and other Hawaiian basalts indicate that those which erupted before or during the period of abundant atmospheric nuclear weapons testing (1950–1970) contain significant levels of Pu (on the order of 1E7 atoms 239Pu/g) with a global fallout Pu isotopic composition, compared to more recent eruptions which incorporated less Pu. Hence, Hawaiian basalts may provide an integrated temporal record of anthropogenic actinide fallout deposition from the atmosphere since eruption.

Characterizing the geogenic background of the Midwest: a detailed mineralogical and geochemical investigation of a glacial till in southwestern Ohio

The state of Ohio has a long history of industrial pollution over numerous decades. Scientific investigations of the sources and impacts of this pollution are becoming increasingly common, particularly in the southwest region of the state, with a strong focus of recent studies being carried out within the context of air, urban soil and sediment quality, and aquatic environments. A key supporting issue in these, and future pollution investigations, is understanding the contribution from, and background concentrations of, natural geogenic materials. A glacial till sampled from Peffer Park, a publicly accessible site in Butler County southwest Ohio, was studied in detail to characterize its mineralogical and geochemical properties. The till sampled, a result of Wisconsin-aged glaciation, represents the regionally extensive glacial drift across the region and is the ideal candidate for targeting in efforts to quantify the background, geogenic environment. Samples were characterized for their elemental abundances using ICP-OES and ICP-MS, while mineralogy was investigated using powder X-ray diffraction, transmission electron microscopy, X-ray computed tomography, and reflective spectroscopy. Chemically, the till sampled is akin to the Earth’s bulk continental crust with characteristic light REE (LREE) enrichment and depleted middle/heavy REE signatures. Of the 39 minor and trace elements analyzed, 74% (n = 29) vary by less than 10 ppm between the 20 sites sampled, and of the ten major element oxides, there is a < 3 wt. % variation with a < 1 wt. % variation observed for seven of the major element oxides. All standard deviations (reported at 2σ) are < 1. Major minerals detected by powder XRD include illite, chlorite (ripidolite), quartz, calcite, dolomite and feldspar minerals with lesser amounts of amphibole, consistent with inferences from bulk chemistry. X-ray computed tomography on a selected sample highlights five orders of magnitude variation with respect to particle size, which is demonstrably skewed toward fine particle size. Accompanying reflective spectral features are dominated by signatures from the high clay mineral (e.g., illite) and carbonate contents, consistent with inferred source materials from the regionally extensive Ordovician stratigraphy associated with the Cincinnati Arch and the ancient crystalline continental basement of Canada. Through a wide variety of analytical techniques, it is demonstrated that the Peffer Park till of southwest Ohio has a remarkably low variation in composition and is highly representative of the geogenic background of this region of the USA. Its characteristics reported here therefore justify its use and application as a broad environmental reference material for the Midwest.

Fluorine determination in biological and environmental samples with INAA using fast neutrons from a p(19 MeV) + Be neutron generator

We present a new activation method based on the 19F(n,2n)18F reaction using fast neutrons produced by a p(19 MeV) + Be accelerator-driven fast neutron source providing continuous neutron spectrum up to 17 MeV with a neutron fluence rate of approximately 9 × 1010 cm−2 s−1 at a 12-µA proton beam current. We describe elimination of interferences in measurement of 18F, a pure positron emitter with T1/2 = 1.83 h. We present results of fluorine determination for several biological and environmental reference materials with the new procedure and compare them with those achieved by other methods in terms of limits of detection, accuracy and precision, where available.

Production of spiked vegetation samples containing γ-emitting radionuclides for proficiency testing

The production of environmental reference materials such as soil, sediment, water and vegetation containing radionuclides for interlaboratory comparison is a vitally important contribution to environmental monitoring. Laboratories that carry out such monitoring need to demonstrate that their results are reliable. The IRD National Intercomparison Program (PNI) produces and distributes reference materials used to check laboratory performance. This work demonstrates the feasibility of producing vegetation (grass) samples containing 60Co, 65Zn, 134Cs, and 137Cs by the spiked sample method. The preparation and the statistical testing of the material followed ISO Guide 35 recommendations (ABNT ISO GUIA 35, 2012). Grass samples were prepared by two different spiking procedures. The activity concentration in the grass for each radionuclidehad a range of 593–683 Bq/kg with uncertainty between 0.6 and 6.2%. Both procedures showed similar results.

Fifteenth International Symposium on Biological and Environmental Reference Materials (BERM-15)

The 15th International Symposium on Biological and Environmental Reference Materials (BERM-15), organized by BAM, took place at in Berlin in September 2018. An overview on main topics of the conference is given.

High‐precision magnesium isotope analysis of geological and environmental reference materials by multiple‐collector inductively coupled plasma mass spectrometry

High-precision magnesium (Mg) isotopic analysis for geological and environmental reference materials is a prerequisite to ensure data quality before using Mg isotopes to trace geochemical and environmental processes. However, the Mg-isotopic ratios of many commonly used reference materials, especially sediments, have rarely been reported. Furthermore, published values for some commonly used reference materials exhibit a significant inconsistency across laboratories and thus need more data comparison. We developed different Mg purification schemes for silicate rocks, high-Ca carbonates and carbonatites, and high-Mn samples because of their significantly different matrices. We then used synthetic solutions to evaluate potential effects on measurement using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The accuracy and precision of our procedures were assessed by measurement on both synthetic solutions and well-studied geostandards. The three different schemes for routine, high-Ca, and high-Mn samples can remove matrices efficiently with nearly 100% Mg yield. However, the presence of acid molarity and concentration mismatch, matrix elements, and fluctuations in room temperature can significantly affect the precision and accuracy of Mg isotope analysis, and must be avoided. The Mg isotopic ratios of reference materials obtained in this study are identical to the previously published values within ±0.06‰, verifying that our procedures are robust. This study presented a thorough set of tests for high precision and accuracy of Mg isotope measurements using MC-ICP-MS, which demonstrate reproducibility and accuracy better than 0.05‰ for δ25 Mg values and 0.06‰ for δ26 Mg values. We reported high-quality Mg isotopic data for 16 geological and environmental reference materials to aid the inter-laboratory calibration of Mg isotope measurements in the future.

Sequential chemical separations and multiple ion counting ICP-MS for 241Pu–241Am–237Np dating of environmental collections on a single aliquot

We have developed a combined sequential chemical separation procedure and multiple ion counting ICP-MS measurement method for isotopic measurements of Am in environmental samples. This, in conjunction with established resin bead TIMS measurements for Pu and Np, allows us to measure long-lived Pu–Np–Am nuclides in environmental samples on a single solution aliquot. This single aliquot method reduces time lines and maximizes sample utility for the measurements, improving sensitivity, precision, and accuracy over prior methods. We have evaluated this new method with environmental reference materials and have obtained accurate results on samples with > 3E6 atoms 241Am.

Reference measurements of cadmium and lead contents in candidates for new environmental certified materials by isotope dilution inductively coupled plasma mass spectrometry

The analytical procedures for the reference measurements of cadmium and lead concentrations in four candidates for new environmental certified reference materials were developed. Cadmium and lead content was determined in bottom sediment (M-2 BotSed), Baltic herring tissue (M-3 HerTis), cormorant tissue (M-4 CormTis) and codfish tissue (M-5 CodTis). The measurements were carried out with the use of a direct isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The isotope dilution approach and the combined uncertainty of results are based on the mathematical equations as from definition of a primary method of measurement. All factors influencing the final results included: the procedural blank, the moisture content in the materials, the factors affecting the blend ratio measurements (instrumental background, spectral interferences, dead time, mass discrimination effects and the repeatability of measured isotopic ratios) as well as the isotopic equilibrium were systematically investigated and included in the uncertainty budget. The content of cadmium in candidates for new environmental reference materials, after correction for moisture contents, matrix separation on ion-exchange resin AG1-X8 of the blended samples and after using for the ICP-MS measurements ratio of pair of isotopes n(110Cd)/n(111Cd) was found to be: (2.18 ± 0.06) μg g−1 in M-2 BotSed, (337 ± 2) ng g−1 in HerTis, (16.4 ± 0.6) ng g−1 in CormTis) and (2.7 ± 0.4) ng g−1 in CodTis, respectively. The content of lead in candidates for new environmental reference materials, after correction for moisture contents, matrix separation on ion-exchange resin AG1-X8 of the blended samples and after using for the ICP-MS measurements ratio of pair of isotopes n(208Pb)/n(207Pb) was found to be: (108 ± 5) ng g−1 in M-3 HerTis, (2.34 ± 0.12) μg g−1 in M-4 CormTis and (43 ± 2) ng g−1 in M-5 CodTis, respectively. The Cd and Pb contents determined in this work were used as a contribution of the Faculty of Chemistry, Biological and Chemical Research Centre University of Warsaw in the characterisation of the abovementioned candidates for new certified reference materials in the frame of the Inter-Laboratory Comparison, organized by the Institute Nuclear Chemistry and Technology (Warsaw, Poland). The obtained excellent agreement within uncertainties with the reference values further validated the methods developed in this study.

Determination of the Mercury Isotopic Ratio by Cold Vapor Generation Sector Field–Inductively Coupled Plasma–Mass Spectrometry Using Lead as the Internal Standard

ABSTRACTLead was applied as an internal standard for the determination of Hg isotopic ratios. Cold vapor generation (CV) coupled with sector field–inductively coupled plasma–mass spectrometry (CV-SF-ICP-MS) was used for determination of Hg. It was effective to avoid interferences of Pb from samples while improving the sensitivity of Hg isotopic analysis by an approximate factor of 45 times higher than the aerosol mode. CV-SF-ICP-MS system was constructed and operational parameters were optimized. Research showed that the long stability of the system was limited by SF-ICP-MS and had no relationship with CV under the optimized conditions. The optimized precision of Hg isotopic ratio analysis was approximately 0.1% during 4 h. Five models were applied for the mass bias correction and the Baxter model obtained the smallest relative difference, 0.52‰. The results showed that the mean value of NIST SRM 3133 Hg isotopic ratios obtained by Pb internal standard was nearly identical with the value for Tl. The same performance was also obtained in two environmental reference materials. The results show that Pb may be used as the internal standard for determination of Hg isotopic ratio instead of Tl.

Multivariate methods for analysis of environmental reference materials using laser-induced breakdown spectroscopy

Analysis of emission from laser-induced plasma has a unique capability for quantifying the major and minor elements present in any type of samples under optimal analysis conditions. Chemometric techniques are very effective and reliable tools for quantification of multiple components in complex matrices. The feasibility of laser-induced breakdown spectroscopy (LIBS) in combination with multivariate analysis was investigated for the analysis of environmental reference materials (RMs). In the present work, different (Certified/Standard) Reference Materials of soil and plant origin were analyzed using LIBS and the presence of Al, Ca, Mg, Fe, K, Mn and Si were identified in the LIBS spectra of these materials. Multivariate statistical methods (Partial Least Square Regression and Partial Least Square Discriminant Analysis) were employed for quantitative analysis of the constituent elements using the LIBS spectral data. Calibration models were used to predict the concentrations of the different elements of test samples and subsequently, the concentrations were compared with certified concentrations to check the authenticity of models. The non-destructive analytical method namely Instrumental Neutron Activation Analysis (INAA) using high flux reactor neutrons and high resolution gamma-ray spectrometry was also used for intercomparison of results of two RMs by LIBS.

Measurements of Rare Earth Element and Other Element Mass Fractions in Environmental Reference Materials (NIST SRM 1646a, NIST SRM 1400, IAEA‐395 and IAEA‐450) by INAA, ICP‐AES and ICP‐MS

INAA, ICP‐AES and ICP‐MS were used to elementally characterise four environmental reference materials – NIST SRM 1646a (Estuarine Sediment), NIST SRM 1400 (Bone Ash), IAEA‐395 (Urban Dust) and IAEA‐450 (Algae). An analytical scheme consisting of the three methods was first applied to NIST SRM 1646a to validate the methodology because it has been extensively analysed and has certified values for many elements. With repeated analyses of NIST SRM 1646a, the accuracy and measurement repeatability of the data obtained were evaluated based on two statistical calculations (zeta‐score and Horwitz ratio) and were observed to be good enough for the analytical scheme to be applied to similar sorts of environmental/geochemical samples. Applying the same approach to NIST SRM 1400, IAEA‐395 and IAEA‐450, enabled mass fractions of 29, 38 and 28 elements to be determined, respectively. Among these results, the data for rare earth elements are of particular interest, not only for IAEA‐450 but also for the other three reference samples. The data for Pr, Gd, Dy, Ho, Er and Tm in NIST SRM 1646a are newly reported in this study. By using small test portions (&lt; 100 mg) for NIST SRM 1646a and IAEA‐395, and recommended minimum amounts for NIST SRM 1400 and IAEA‐450, sample homogeneity was evaluated.

Chemical vapor generation coupled with atomic fluorescence spectrometry for the determination of manganese in food samples

A novel method based on chemical vapor generation (CVG) coupled with atomic fluorescence spectrometry (AFS) for the determination of manganese was developed. Room temperature ionic liquids (RTILs) combined with ammonium pyrroldinedithiocarbamate (APDC) were used to synergetically enhance the CVG of Mn. Volatile species of Mn were effectively generated through reduction of acidified analyte solutions in the presence of 0.1% (m/v) APDC and 0.1% (v/v) 1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM]PF6) with 2.0% (m/v) KBH4 and 0.1% (m/v) phenanthroline mixed solution. The efficiency for the CVG of manganese was 44%. Some parameters that influenced CVG and subsequent determination were evaluated in detail, such as the concentrations of RTILs, APDC, phenanthroline, nitric acid (HNO3) and KBH4; lengths of reaction tube and transfer tube, as well as interferences. Under optimized experimental conditions, the detection limit (LOD) of Mn(II) was 1.5ngmL−1. Relative standard deviations for five replicate determinations of the standard solution containing 100ngmL−1 Mn(II) was 4.3%. The proposed method was successfully applied to the determination of Mn in water sample and certified environmental reference materials with satisfactory results.

Roadmap for radioanalytical reference and performance evaluation materials for current and emerging issues

Reference materials are fundamental tools for radiochemistry measurements laboratories to establish and evaluate analytical methods, test measurement capabilities, quantify radionuclides, compare analytical results, and establish legal confidence defensibility in measurement results. Over the past decades the focus of low-level environmental reference material producers have adapted to evolving national and international priorities and needs. This document provides a Roadmap of high priority current and future low-level radionuclide Certified Reference and Performance Evaluation Materials that subject-matter experts have identified at NIST and other public workshops (Blueprints) as crucial to metrologists and program directors to address national and international issues.

Ion Exchange Chromatography and Mass Bias Correction for Accurate and Precise Zn Isotope Ratio Measurements in Environmental Reference Materials by MC-ICP-MS

Precise and accurate d66/64Zn data for environmental reference materials (RMs) including rocks, sediments, soils and plants are presented in order to improve the metrological traceability and analytical control of Zn isotope ratio determinations in future environmental studies. Previously developed ion exchange chromatography protocols were adjusted to enable faster sample throughput and instrumental mass bias processes were investigated. The improved chromatographic protocol yielded precise and quantitative recoveries (99 ± 7%, σ, n = 16), while the mass bias correction using Cu as external dopant provided precisions better than 0.02‰, 2σ, n = 7. Investigations into spectral and non-spectral interferences identified significant formation of Cr and Ti oxides and hydroxide ionic species. Analysis of six RMs (BHVO-2 basalt (USGS), BCR-2 basalt (USGS), AGV-2 andesite (USGS), 2709 San Joaquin soil (NIST), 1646a estuarine sediment (NIST) and 1573a tomato leaves (NIST)) showed good reproducibility (< 0.01‰, 2s, 5 ≤ n ≥ 1).

Preparation and certification of two freshwater sediments certified reference materials for polycyclic aromatic hydrocarbons

Two freshwater sediments certified reference materials (CRMs) for 16 polycyclic aromatic hydrocarbons (PAHs) have been developed by the Institute for Environmental Reference Materials (IERM) of Ministry of Environmental Protection (MEP) in China. The methodology for preparing the CRMs of PAHs in sediments is described in this paper. The collected natural sediment samples were air-dried, ground, homogenised, packed, sterilised and tested on stability and homogeneity. Homogeneity results showed that the between-unit variation was confirmed to be below 4.5% for each compound. Stability was assessed after storage of samples for 16 months at temperature less than 30°C and in shade. The certification of the natural sediment matrix CRMs for PAHs was based on the agreement of results using different analytical techniques including gas chromatography/mass spectrometry (GC/MS) and reversed-phase liquid chromatography (LC) by no less than eight collaborating laboratories including IERM. Results of the homogeneity showed that the calculated ubb′ was 0.9–2.5% for environmental river standard-4 (ERS-4) and 9–2.3% for environmental lake standard-1 (ELS-1), whereas stability results of total 16 PAHs indicated that the calculated urel,lts was 4.2% for ERS-4 and 2.2% for ELS-1. Certified values of 16 PAHs in ERS-4 varied from 8.5 to 167 μg/kg and ranged from 0.036 to 2.8 mg/kg in ELS-1.The good comparability, together with the independent confirmation of the assigned mass fraction by using different methods, confirmed that the CRMs are suitable for the method validation and quality control in soil or sediments analysis.

Determination of Mercury in One Hundred and Sixteen Geological and Environmental Reference Materials Using a Direct Mercury Analyser

The mercury content of 116 reference materials (RMs) from ten international organisations was determined in this study, which focused on variability within and between batches of RMs. Direct mercury analysis (DMA) was applied to RMs having Hg contents between 1 and 6300 ng g−1 and provided good precision and accuracy. Accuracy was demonstrated by the agreement of our results with certified values, while replicates were made to establish the precision. Low within-batch variability was noted, with precision from 0.1 to 23% (n = 3–5) apparently depending on Hg content and homogeneity, whereas systematic offsets were detected among several batches. Thanks to the analysis of different batches; the homogeneity or heterogeneity of several RMs was shown, and thus, suitable RMs for quality control for Hg determinations could be recommended. La concentration en mercure a ete determinee dans 116 materiaux de reference (RMs) geologiques et environnementaux issus de 10 organisations internationales. Notre etude porte sur la variabilite intra et inter lots de materiaux de reference dont les concentrations en mercure varient de 1 a 6300 ng g−1. Les mesures ont ete effectuees avec un analyseur direct de mercure. La justesse des resultats a ete demontree par comparaison aux valeurs certifiees et la fidelite par la realisation de replicats d'analyse. Une faible variabilite au sein d'un meme lot a ete etablie pour l'ensemble des RMs, apparemment dependante de la concentration en Hg et de l'homogeneite des echantillons, l'ecart-type relatif varie de 0.1 a 23% (n = 3 a 5), alors qu'une dispersion importante a ete constatee pour nombreux d'entre eux entre les bouteilles. L'analyse de lots distincts a permis la mise en evidence de l'homogeneite ou de l'heterogeneite de plusieurs RMs et nous recommandons donc l'utilisation des materiaux de reference adequates pour les controle qualite lors de l'analyse du Hg.