Working Reference Materials Research Articles

Assessing the performance of international laboratories analysing the stable isotope composition (δ15 N, δ18 O, δ17 O) of nitrate in environmental waters.

Stable-isotope analyses of nitrate (NO3 - ) in various water sources are crucial for understanding nitrogen pollution and its impact on aquatic ecosystems. We evaluated the accuracy and precision of stable-isotope analyses of nitrate conducted by international laboratories. Six samples with nitrate (2 mg L-1 NO3 - -N) were sent to 47 laboratories. The NO3 - had a 30-50 ‰ range of δ values for δ15 N, δ18 O and δ17 O. One blind duplicate evaluated reproducibility and the effect of water δ18 O. Laboratories used diverse methods to convert nitrate to N2 O, N2 , CO or O2 for stable-isotopic measurements (microbial, cadmium, titanium and elemental analysis) and isotope-ratio mass spectrometry or laser-based technologies. Thirty-six international laboratories (83 %) reported results; however, 23 % did not analyze the test samples due to technical difficulties. Of the reporting laboratories, 79 % and 84 % produced accurate δ15 N and δ18 O results falling within ±0.8 ‰ and ±1.1 ‰ of the benchmark values, respectively. Three laboratories produced only outliers. The duplicate revealed most laboratories gave internally reproducible results at appropriate analytical precision. For δ17 O, six laboratories reported results, but 67 % could not reproduce results within their claimed analytical measurement precision. One complication is a lack of nitrate reference materials for δ17 O. Analyst experience contributed to better performance, and underperformance was from compromised standards or inappropriate δ range of working reference materials. The stable isotope community must develop new nitrate reference materials for δ15 N spanning -20 ‰ to +80 ‰ and new materials for δ17 O.

Spatially Resolved Characterisation of Low Mass Fraction Uranium Glass Working Reference Materials

We present the results of a study to generate reference glasses that reflect an environment analogous to historic nuclear fallout samples of interest for post‐detonation nuclear forensics. The glasses were generated by melting and then quenching SiO2, Al2O3 and CaCO3 powders. Two suites of glasses with three distinct U isotopic ratios were successfully made with enrichments in the 235U isotope (~ natural [0.72%], ~ 53% and 94%), but the bulk elemental data showed heterogeneity (~ 10% RSD) with U mass fractions ranging from 331.47 to 373.63 μg g‐1. Spatially resolved U isotopic measurements were performed using three mass spectrometry techniques (secondary ion mass spectrometry‐single stage accelerator mass spectrometry [SIMS‐SSAMS], large geometry [LG] ‐ SIMS, and laser ablation‐inductively coupled plasma‐mass spectrometry [LA‐ICP‐MS]) across five National Laboratories. The results showed good agreement with the bulk U isotopic data for the low, medium, and high U mass fractions. We conclude that despite elemental heterogeneity, these samples can serve as useful working reference materials for spatially resolved nuclear fallout analyses, as well as for other related spatially resolved analyses.

Cloud point extraction assisted spectrophotometric quantification of trace boron impurity in uranium-based nuclear fuels

The separation of boron in nuclear fuels by cloud point extraction (CPE) has been a challenge due to high acidity of digested sample solutions. High acidity hampers the coacervation of micelles. As a result, the cloud point temperature increases and thus could cause the inevitable loss of boron as volatile species. Herein we have proposed a novel CPE-assisted colorimetric method for the quantification of traces of boron (B) in uranium-based fuels. A 1:1 mixture of 2-ethyl hexane-1,3-diol (EHD) and curcumin dispersed in Triton X-114 surfactant was used in the proposed CPE process. We had investigated several compounds to act as micelle surface modifiers. Among them, only bromine water (Br2) was found not only to lower the cloud point temperature (CPT, from 80 °C to 42 ± 2 °C) but also resulted in the quantitative recovery of boron (≥95%). The CPE of boron from uranium matrix in a 2.0 mol L−1 HCl medium was suitable for direct chemical quality assurance of routine uranium-based fuels. The molar extinction coefficient of the boron-EHD-curcumin complex was found to be 4.75 × 105 L mol−1 cm−1 (λmax at 458 nm) in N,N-dimethyl formamide medium. The linear dynamic range and detection limit of the proposed analytical procedure were calculated to be 10–150 ng mL−1 and 0.8 ng mL−1 respectively. The proposed analytical methodology was validated by analysis of three in-house working reference materials of uranium. Determination of traces of boron in two uranium dioxide and two metallic uranium samples were found to demonstrate the applicability of the method. The relative standard deviation of the proposed method was found to be of 3–5%.

Progress and challenges in dual- and triple-isotope (δ18 O, δ2 H, Δ17 O) analyses of environmental waters: An international assessment of laboratory performance.

Stable isotope analyses of environmental waters (δ2 H, δ18 O) are an important assay in hydrology and environmental research with rising interest in δ17 O, which requires ultra-precise assays. We evaluated isotope analyses of six test water samples for 281 laboratory submissions measuring δ2 H and δ18 O along with a subset analyzing δ17 O and Δ17 O by laser spectrometry and isotope ratio mass spectrometry (IRMS). Six test waters were distributed to laboratories spanning a wide δ range of natural waters for δ2 H, δ18 O and δ17 O and Δ17 O. One sample was a blind duplicate to test reproducibility and claims of analytical precision. Results showed that ca 83% of the submissions produced acceptable δ18 O and δ2 H results within 0.2‰ (mUr) and 1.6‰ of the benchmark values, respectively. However, 17% of the submissions gave questionable to unacceptable results. A blind duplicate revealed many laboratories reported overly optimistic precision, and many could not replicate within their claimed precision. For Δ17 O, dual-inlet results for IRMS using quantitative O2 conversion were accurate and highly precise, but the results for laser spectrometry ranged by ca 200 per meg (μUr) for each sample, with ca 70% unable to replicate the duplicate to their claimed Δ17 O precision. One complicating factor is the lack of certified primary reference waters for δ17 O. No single factor or combination of factors was identifiable for poor or good performance, and underperformance came from issues like data normalization including inadequate memory and drift corrections, compromised working reference materials and underperforming instrumentation. We recommend isotope laboratories include high and low δ value controls of known isotope composition in each run. Progress in Δ17 O analyses by laser spectrometry requires extraordinary proof of performance claims and would benefit from the development of adoptable and systematic advanced data processing procedures to correct for memory and drift.

Performance of low-cost stainless-steel beverage kegs for long-term storage integrity and easy dispensing of water isotope (δ18 O, δ2 H) reference materials.

A widespread problem observed in global water isotope (δ18 O, δ2 H) proficiency tests is compromised working reference materials due to storage-dispensing evaporation effects. Proper storage requires no evaporation or leakage, which causes isotopic drift and bias. Surveys by the International Atomic Energy Agency (IAEA) show most isotope laboratories use glass or plastic bottles to store working reference materials, with frequent opening and closings that pose evaporation risks. Practical small (ca. 2-5 L) storage-dispensing solutions free of air exposure, evaporation, and leakage are needed. We also tested several smaller-scale bottles for day-to-day aliquots. We tested low-cost, conveniently sized (4 L) adaptations of a common stainless-steel beverage keg with a liquid dispenser, with minor modifications to facilitate low-flow dispensing and pressurization (1-2bar) with Ar or N2 . We tested three kegs (100%, 75%, 50% initial fills) for a 2-year period along with monthly dispensing to assess long-term storage viability for maintaining δ18 O and δ2 H integrity and dispensing, and day-to-day aliquot bottles for 6months. Test results showed these small keg storage systems fully maintained the isotopic integrity of water over the 2-year testing period with no trend in the isotopic data that would reveal evaporative loss or leakage (e.g., pressure or mass loss) regardless of starting fill level. However, evaporated water in the outlet tube assembly must be eliminated by discarding 15-20 mL before dispensing into appropriate daily-use laboratory standard bottles (30-100 mL). Glass bottles for daily aliquots showed good integrity properties, but only if their fill level was >50%. The use of a low-cost pressurized metal beverage keg dispensing system provides a robust solution to enable laboratories to maintain the integrity of their water isotope working reference materials over several years.

International reference preparations for standardization of biological medicinal products.

International standards are prepared as materials assigned an arbitrary unitage for a biological activity by the Expert Committee on Biological Standardization of the World Health Organization. Working reference materials are calibrated against international standards giving a common unit of measurement between laboratories. The references are assessed by a collaborative study including all relevant assays rather than by a single reference method as in the SI (Le Système international d'unités) system and the unitage assigned is an arbitrary value derived from a consensus of all valid methods. The process has proved valuable in assaying the activity of therapeutic biological medicines and in standardizing certain types of diagnostics. Issues arise with maintaining the unit when the primary reference must be replaced and to some extent in assessing the commutability of the reference with real life analytes.

Traceable Determination of the Absolute <newline/>Neutron Emission Yields of <formula formulatype="inline"><tex Notation="TeX">${{\rm UO}_2}{{\rm F}_2}$</tex></formula> <newline/>Working Reference Materials

The nuclear material contained in the process equipment of a uranium enrichment plant (referred to as holdup) is an important component of the overall nuclear material inventory for the plant. Accurate quantification and verification of holdup is needed to improve international safeguards and nuclear material accountancy. This is also needed for criticality safety and waste disposition. Passive neutron and gamma-ray nondestructive assay (NDA) methods are used to measure the holdup in process equipment. A key advantage of neutron measurements is that neutrons are highly penetrating and can be measured through thick walled equipment. The dominant source of neutrons in the UO2F2 holdup is from the 19F(α,n)22Na reaction resulting from 234U alpha decay when uranium is enriched. There is a considerable spread between different historic determinations of the 19F(α,n) yield from uranium which limits the accuracy of modeling and the calibration of NDA instruments. Furthermore, the compound form and presence of water also significantly affects the neutron emission rate from the holdup. This paper describes a series of experimental measurements performed at Los Alamos National Laboratory (LANL) to determine the absolute neutron emission yield from 10 different UO2F2 working reference materials (WRMs) fabricated at the Portsmouth Gaseous Diffusion Plant (PGDP). The Mini Epithermal Neutron Multiplicity Counter (Mini ENMC) and a NIST certified 252Cf neutron source were used for these measurements. The high efficiency and short die-away time of the Mini ENMC provides the high measurement precision needed to certify the neutron emission yield. The experiment was designed to achieve sub 1% accuracy in the net counting rate on each item and to provide assurance that important factors such as instrument stability, item placement and background were well understood. The traceable neutron yields measured from the WRMs were used to determine a more accurate neutron yield for the UO2F2 material. The results were compared to historical neutron emission rates. The F(α,n) data obtained from these measurements directly supports nuclear safeguards for NDA of uranium holdup and provides a more accurate calibration for new and existing NDA detector systems.

Offline oxygen isotope analysis of organic compounds with high N:O

Although the advantages of online δ(18)O analysis of organic compounds make its broad application desirable, researchers have encountered NO(+) isobaric interference with CO(+) at m/z 30 (e.g. (14)N(16)O(+), (12)C(18)O(+)) when analyzing nitrogenous substrates. If the δ(18)O value of inter-laboratory standards for substrates with high N:O value could be confirmed offline, these materials could be analyzed periodically and used to evaluate δ(18)O data produced online for nitrogenous unknowns. To this end, we present an offline method based on modifications of the methods of Schimmelmann and Deniro (Anal. Chem. 1985; 57: 2644) and Sauer and Sternberg (Anal. Chem. 1994; 66: 2409), whereby all the N(2) from the gas products of a chlorinated pyrolysis was eliminated, resulting in purified CO(2) for analysis via a dual-inlet isotope ratio mass spectrometry system. We evaluated our method by comparing observed δ(18)O values with previously published or inter-laboratory calibrated δ(18)O values for five nitrogen-free working reference materials; finding isotopic agreement to within ±0.2‰ for SIGMA® cellulose, IAEA-CH3 cellulose (C(6)H(10)O(5)) and IAEA-CH6 sucrose (C(12)H(22)O(11)), and within ±1.8‰ for IAEA-601 and IAEA-602 benzoic acids (C(7)H(6)O(2)). We also compared the δ(18)O values of IAEA-CH3 cellulose and IAEA-CH6 sucrose that was nitrogen-'doped' with adenine (C(5)H(5)N(5)), imidazole (C(3)H(4)N(2)) and 2-aminopyrimidine (C(4)H(5)N(3)) with the undoped δ(18)O values for the same substrates; yielding isotopic agreement to within ±0.7‰. Finally, we provide an independent analysis of the δ(18)O value of IAEA-600 caffeine (C(8)H(10)N(4)O(2)), previously characterized using online systems exclusively, and discuss the reasons for an average 1.4‰ enrichment in δ(18)O observed offline relative to the consensus online δ(18)O value.

Comprehensive inter‐laboratory calibration of reference materials for δ18O versus VSMOW using various on‐line high‐temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high-temperature conversion techniques (HTC)a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125 per thousand, an artificially enriched reference water (delta(18)O of +78.91 per thousand) and two barium sulfates (one depleted and one enriched in (18)O) were prepared and calibrated relative to VSMOW2b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded: Reference material delta(18)O and estimated combined uncertainty IAEA-602 benzoic acid+71.28 +/- 0.36 per thousand USGS 35 sodium nitrate+56.81 +/- 0.31 per thousand IAEA-NO-3 potassium nitrate+25.32 +/- 0.29 per thousand IAEA-601 benzoic acid+23.14 +/- 0.19 per thousand IAEA-SO-5 barium sulfate+12.13 +/- 0.33 per thousand NBS 127 barium sulfate+8.59 +/- 0.26 per thousand VSMOW2 water 0 per thousand IAEA-600 caffeine-3.48 +/- 0.53 per thousand IAEA-SO-6 barium sulfate-11.35 +/- 0.31 per thousand USGS 34 potassium nitrate-27.78 +/- 0.37 per thousand SLAP water-55.5 per thousand The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3-fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for delta(18)O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen-isotope ratios (delta(18)O) of nitrates, sulfates, or organic material should explicitly state in their reports the delta(18)O values of two or more internationally distributed nitrates (USGS 34, IAEA-NO-3, and USGS 35), sulfates (IAEA-SO-5, IAEA-SO-6, and NBS 127), or organic material (IAEA-601 benzoic acid, IAEA-602 benzoic acid, and IAEA-600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the delta(18)O values at a later time should it become necessary.The high-temperature reduction technique for analyzing delta(18)O and delta(2)H is not as widely applicable as the well-established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible.

Development of working reference materials for clinical virology

Nucleic acid amplification technique (NAT)-based assays are replacing traditional diagnostic methods in clinical laboratories. However, many of these assays are developed in-house and the lack of standardised reference materials has hindered assay implementation and control. Consequently, in the UK, the Clinical Virology Network (CVN), the National Institute for Biological Standards and Control (NIBSC), and the Health Protection Agency (HPA), are working in collaboration to develop working standards or ‘run controls’ for diagnostic NAT-based assays, particularly real-time PCR. These run controls are intended for use in microbiology laboratories and are designed to be extracted and amplified in the same way as clinical samples and included in each assay run. The aim is to enable clinical laboratories to continuously monitor the performance of their diagnostic NAT assays on a run-by-run basis allowing inter-laboratory comparisons, and ultimately improving the consistency of results. At present, eight candidate run controls representing clinically relevant viral targets have been prepared for evaluation by CVN laboratories. Data have been returned on the performance of each run control in routine diagnostic assays. Preliminary results presented here indicate a high level of variability in intra- and inter-assay detection of these targets, highlighting the need for standardisation of assays within molecular diagnostics.

Summary of ISO/TC 201 Standard: XIX ISO 17331:2004—Surface chemical analysis—Chemical methods for the collection of elements from the surface of silicon‐wafer working reference materials and their determination by total‐reflection x‐ray fluorescence (TXRF) spectroscopy

AbstractThis international standard specifies chemical methods for the collection of iron and/or nickel from the surface of silicon‐wafer working reference materials by the vapour‐phase decomposition method or the direct acid droplet decomposition method. The determination of the elements collected may be carried out by total‐reflection x‐ray fluorescence spectroscopy, as well as by graphite‐furnace atomic absorption spectroscopy or inductively coupled plasma mass spectroscopy. This international standard applies to iron and/or nickel atomic surface densities from 6 × 109 to 5 × 1011 atoms cm−2. Copyright © 2005 John Wiley & Sons, Ltd.

Radiometric measurements on non-destructive assay standards fabrication for WIPP Performance Demonstration Program

The Inorganic Elemental Analysis Group of LANL has prepared several different sets of working reference materials (WRMs). These WRMs are prepared by blending quantities of nuclear materials (plutonium, americium, and enriched uranium) with diatomaceous earth. The blends are encapsulated in stainless steel cylinders. These WRMs are being measured as blind controls in neutron and gamma based non-destructive assay (NDA) instruments. Radiometric measurements on the blending homogeneity and verification on a set of sixty-three plutonium based WRMs are discussed in this paper.

Determination of Hydrogen in Steel by Using a Levitation Melting Method

A new quantitative technique for determination of hydrogen in steels has been developed using levitation, which permits flotation and melting of samples by magnetic pressure under application of a high-frequency magnetic field to steel specimens. Steel samples are melted in a state of levitation in a flow of nitrogen gas. The discharged hydrogen gas is detected and measured quantitatively with a thermal conductivity detector. This method needs no crucible because the melting occurs in flotation. A cylindrical-shaped steel sample of 6 mm diameter and 6 mm length (about 1.5 g) was melted using the levitation melting technique. Radio frequency power of 1.5 kW with 200 kHz was applied to the levitation coil. Hydrogen was completely extracted within 1 min after melting. Working reference materials of stainless steel samples were analyzed in order to evaluate the present analytical method. The calibration curve showed an excellent linearity in a range of 0.4−6.7 μg/g, with a relative standard deviation of about...