Environmental monitoring as an important tool for safeguards of nuclear material and nuclear forensics

Summary The use of environmental monitoring as a technique to identify activities related to the nuclear fuel cycle has been proposed by international safeguards organizations. The elements specific for each kind of nuclear activity, or “nuclear signatures”, inserted in the ecosystem can be intercepted by different live organisms. This work demonstrates the technical viability of using pine needles as bioindicators of nuclear signatures associated with uranium enrichment activities. Additionally, it proposes the use of HR-ICP-MS to identify the signature corresponding to that kind of activities in the ecosystem. Nitric acid solutions, used to wash pine needles sampled near nuclear facilities and containing only 0.1 mg ^. kg^-1 of uranium, exhibit a n(²³⁵U)/n(²³⁸U) isotopic abundance ratio of 0.0092±0.0002, while solutions originated from samples collected at places located more than 200 km far from activities related to the nuclear fuel cycle exhibit a value of 0.0074±0.0002. Similar results were obtained for sample solutions prepared using the acid leaching process. The different values of n(²³⁵U)/n(²³⁸U) isotopic abundance ratio obtained permit to confirm the presence of anthropogenic uranium and demonstrate the viability of using the methodology proposed in this work.     

Isotopic “fingerprints” for natural uranium ore samples

A set of six samples, collected worldwide from various uranium ore mining facilities, was analysed for uranium isotopic composition by high accuracy isotope mass spectrometry. The goal of this article was twofold: to measure isotopic variations between samples of different geographical origin and to produce calibrated isotope ratios with the smallest achievable uncertainty (as defined according to the ISO Guide to the Expression of Uncertainty in Measurement). In the first step, the molar ratio of the isotopes ²³⁵U and ²³⁸U, n(²³⁵U)/n(²³⁸U), was measured using a UF₆-gas-inlet isotope mass spectrometer (VARIAN MAT 511). This instrument was calibrated against gravimetrically prepared synthetic isotope mixtures thus allowing SI-traceable measurements to be made. The ratios of the “minor isotopes” to ²³⁸U [n(²³⁴U)/n(²³⁸U) and n(²³⁶U)/n(²³⁸U)] were determined in a second step using a thermal ionisation mass spectrometer with high abundance sensitivity (Finnigan MAT262-RPQ-PLUS). The mass-fractionation correction was done internally using the result of the n(²³⁵U)/n(²³⁸U) measurement. As a result, the complete measured uranium isotopic composition is traceable to the SI system. For all ratios n(²³⁴U)/n(²³⁸U), n(²³⁵U)/n(²³⁸U), and n(²³⁶U)/n(²³⁸U) significant differences for samples of different origin were found. Regarding the n(²³⁶U)/n(²³⁸U) results, only two samples, one of them from the Oklo reactor in Gabon, showed significant presence of ²³⁶U. For all other samples an upper limit for n(²³⁶U)/n(²³⁸U) of about 6 × 10⁻¹⁰, mainly dependent on the instrumentation, was found. As a result of this study we propose values for the isotope abundances of natural uranium for the “Best Measurement from a Single Terrestrial Source” and the “Range of Natural Variations” in the IUPAC-table of the “Isotopic Composition of the Elements.”     

Measurement of non-separated U/Pu samples: optimization of TIMS procedures for safeguards purposes at Rokkasho on-site laboratory

The on-site laboratory (OSL) at Rokkasho Reprocessing Plant (RRP) is jointly operated by the Japanese authority Nuclear Material Control Centre and the International Atomic Energy Agency (IAEA) and provides, together with the Nuclear Material Laboratory (NML) at Seibersdorf, analytical services to the IAEA’s inspectorate. OSL deals with a variety of samples typical to a reprocessing plant including pure product solutions of uranium and plutonium but also mixed U/Pu solutions originating from various stages of the chemical process. For a significant proportion of the samples, the requirement on measurement accuracy and precision from the Inspectorate makes the use of thermal ionization mass spectrometry (TIMS) indispensible. Until recently, all samples intended for TIMS had to undergo time-consuming U/Pu separation before isotope dilution measurement. The need for rapid reporting of analytical results for certain safeguards samples evoked the idea of performing TIMS measurements without prior U/Pu separation for mixed U/Pu products as they are obtained from the PUREX process at RRP. For this purpose, a systematic study was initiated to probe the figure of merits and limitations of conducting TIMS analyses on mixed U/Pu samples and, in particular, whether the accuracy and precision of the main ratios of interest, n(²³⁵U)/n(²³⁸U) and n(²⁴⁰Pu)/n(²³⁹Pu), are influenced by the presence of larger amounts of the other element. A series of synthetic mixtures with U/Pu ratios ranging from 1:10 up to 100:1 were prepared and measured in both laboratories—OSL and NML—using ThermoFisher TRITON multi-collector TIMS instruments. For the n(²³⁵U)/n(²³⁸U) ratio, interference due to ²³⁸Pu was observed which can be significant depending on the U/Pu ratio and the ²³⁸Pu abundance. However, for the n(²⁴⁰Pu)/n(²³⁹Pu) ratio, which is of premier importance for safeguarding RRP, no significant interference arising from the concomitant U was detected independently of enrichment. Even in samples with an excess of U (U/Pu ratio of 100:1), compliance with International Target Values (ITV2010) was demonstrated for n(²⁴⁰Pu)/n(²³⁹Pu) results with a relative difference to certified not exceeding 0.01 %.     

The use of LA-SF-ICP-MS for nuclear forensics purposes: uranium isotope ratio analysis

This work describes the utilization of the laser ablation sector field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS) technique for the determination of uranium isotopic composition in a highly enriched uranium sample. The measurements were performed on a continuous ablation with low energy density and defocusing, which demonstrated to be the optimum to reach the best signal stability. The measurements were improved by adjusting the following parameters: RF power, laser beam diameter, defocusing of laser beam, laser energy, laser energy density, auxiliary gas and sample gas. The ²³⁵U/²³⁸U isotope ratio with its respective uncertainty was 16.36 ± 0.15 and its precision was 1.12 % relative standard deviation. The uncertainties were estimated following the ISO GUM, with a confidence level of 95.45 % (k = 2.00). When compared the isotope abundances to the Round Robin Exercise Number 3’s average results a difference of 0.46 % has been found and when compared to supplier’s value, the difference was 0.41 %. The results presented by the measurements revealed that the LA-ICP-MS technique offers a rapid and accurate alternative to measure uranium isotope ratios without any sample preparation, since it allows carrying out the measurements straight on the sample. Moreover, it preserves the testimony—very important for safeguards and nuclear forensics purposes.     

Experimental k 0 and k 0-fission factors for the determination of the n(235U)/n(238U) enrichment levels and correction for 235U fission interferences in samples containing uranium

In 2010 we investigated the applicability of the current k ₀ and k ₀-fission factors for the determination of the n(²³⁵U)/n(²³⁸U) isotopic ratio in multi-elemental samples containing uranium. An overestimation 3–4 % was observed in our determinations when employing the recommended 2003 k ₀-literature. After a recalibration of all our laboratory instruments, a 3 % overestimation was still observed in this work when employing this nuclear data. Therefore we aimed at the experimental re-determination of these composite nuclear constants in order to enhance the reliability of the isotopic ratio determination method and the accuracy of our data-filtering algorithms. New k ₀-fission factors are given for 7 nuclides that are not currently present in the 2012 k ₀-database. Several additional k ₀ factors are introduced for some nuclides in this library. Our k ₀ results are also compared with those recently reported by Blaauw et al.     

Using the 186-keV peak for 226Ra activity concentration determination in Hungarian coal-slag samples by gamma-ray spectroscopy

The uranium isotopic abundance and the ²³⁸U–²²⁶Ra secular equilibrium were determined in nine Hungarian coal slag samples. The ²²⁶Ra activity concentration was measured based on the radon decay products and also the ²²⁶Ra peak at 186 keV. Secular equilibrium existed in eight samples, whereas one sample showed a slight disequilibrium. The direct and fast measurement using only the 186 keV peak was validated which can be used after measuring the uranium isotopic ratio and verifying the ²³⁸U–²²⁶Ra secular equilibrium. This method can be used to measure the ²²⁶Ra content of high number of samples from the same geochemical background.     

Measurement of production date (age) of nanogram amount of uranium

JRC-Karlsruhe obtained a swipe sample from a highly enriched uranium seizure, which had taken place in 2011. Due to the very low amount of uranium (nanograms) a new method needed to be developed to determine the U production date (age). The particles on the swipe were collected on a pyrolytic graphite planchet using a vacuum impactor and they were subsequently leached with ccHNO₃. The “bulk” U isotopic composition (²³⁵U: 72.51?±?0.03 wt%) and the production date (December 1992?±?1 year) determined by MC-ICP-MS indicated that the material showed similarity with two other HEU cases seized earlier in Europe.

     

Alpha spectrometric evaluation of SRM-995 as a potential uranium/thorium double tracer system for age-dating uranium materials

Uranium-233 (t _1/2 ~ 1.59E5 years) is an artificial, fissile isotope of uranium that has significant importance in nuclear forensics. The isotope provides a unique signature in determining the origin and provenance of uranium-bearing materials and is valuable as a mass spectrometric tracer. Alpha spectrometry was employed in the critical evaluation of a ²³³U standard reference material (SRM-995) as a dual tracer system based on the in-growth of ²²⁹Th (t _1/2 ~ 7.34E3 years) for ~35 years following radiochemical purification. Preliminary investigations focused on the isotopic analysis of standards and unmodified fractions of SRM-995; all samples were separated and purified using a multi-column anion-exchange scheme. The ²²⁹Th/²³³U atom ratio for SRM-995 was found to be 1.598E?4 (±4.50 %) using recovery-corrected radiochemical methods. Using the Bateman equations and relevant half-lives, this ratio reflects a material that was purified ~36.8 years prior to this analysis. The calculated age is discussed in contrast with both the date of certification and the recorded date of last purification.     

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.     

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The ²³⁶U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF–ICP–MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF–ICP–MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4×10^–4 and 10^–3 counts per atom were achieved for ²³⁸U in DF–ICP–QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH⁺/U⁺ was 1.2×10^–4 and 1.4×10^–4, respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 μg L^–1 NBS U-020 standard solution was 0.11% (²³⁸U/²³⁵U) and 1.4% (²³⁶U/²³⁸U) using a MicroMist nebulizer and 0.25% (²³⁵U/²³⁸U) and 1.9% (²³⁶U/²³⁸U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the ²³⁶U/²³⁸U ratio ranged from 10^–5 to 10^–3. Results obtained with ICP–MS, α- and γ-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.     

Study of uranium isotopic composition in groundwater and deviation from secular equilibrium condition

Uranium concentration in groundwater reflect both redox conditions and uranium content in host rock. In the present study an attempt has been made to study the uranium concentration and activity ratios of uranium isotopes to present the geochemical conditions of the groundwater in Malwa region of Punjab state, India and the reason for high uranium levels and variation of activity ratios from secular equilibrium conditions. Uranium concentration in groundwater samples was found to be in the range of 13.9 ± 1.2 to 172.8 ± 12.3 μg/l with an average value of 72.9 μg/l which is higher than the national and international guideline values. On the basis of uranium concentration, the groundwater of the study region may be classified as oxidized aquifer on normal uranium content strata (20 %) or oxidized aquifer on enhanced uranium content strata (80 %). The ²³⁸U, ²³⁵U and ²³⁴U isotopic concentration in groundwater samples was found to be in the range of 89.2–1534.5, 4.4–68.5, and 76.4–1386.2 mBq/l, respectively. Activity ratios of ²³⁴U/²³⁸U varies from 0.94 to 1.85 with a mean value of 1.11 which is close to unity that shows secular equilibrium condition. High value of ²³⁴U isotope than ²³⁸U may be due to alpha recoil phenomenon. The plot of AR of ²³⁴U/²³⁸U against the total uranium content in log scale reveals that the groundwaters of the study region either belongs to stable accumulation or normal oxidized aquifer.     

Sorption of uranium using silica gel with benzoylthiourea derivatives

Benzoylthiourea derivatives (N,N-diphenyl-N′-(3-methylbenzoyl)thiourea and diphenyl-N′-(4-methylbenzoyl)thiourea) were impregnated onto silica gel. The preconcentration of uranium(VI) from aqueous solution was investigated. Extraction conditions were optimized in batch method prior to determination by uv–visible absorption spectrometry using arsenazo(III). The optimum pH for quantitative adsorption was found as 3–7. Quantitative recovery of uranium (VI) was achieved by stripping with 0.1 mol L^?1 HCl. Equilibration time was determined as 30 min for 99% sorption of U(VI). Under optimal conditions, dynamic linear range of for U(VI) was found as 0.25–10 μg mL^?1. The relative standard deviation as percentage and detection limit were 5.0% (n = 10) for 10 μg mL^?1 U(VI) solution and 8.7 ng mL^?1, respectively. The method was employed to the preconcentration of U(VI) ions in soil and tap water samples.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

A novel isotope analysis of oxygen in uranium oxides: comparison of secondary ion mass spectrometry,glow discharge mass spectrometry and thermal ionization mass spectrometry

The natural variation of the oxygen isotopic composition is used among geologists to determine paleotemperatures and the origin of minerals. In recent studies, oxygen isotopic composition has been recognized as a possible tool for identification of the origin of seized uranium oxides in nuclear forensic science. In the last 10 years, great effort has been made to develop new direct and accurate n(¹⁸O)/n(¹⁶O) measurements methods. Traditionally, n(¹⁸O)/n(¹⁶O) analyses are performed by gas mass spectrometry. In this work, a novel oxygen isotope analysis by thermal ionization mass spectrometry (TIMS), using metal oxide ion species (UO⁺), is compared to the direct methods: glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS). Because of the possible application of the n(¹⁸O)/n(¹⁶O) ratio in nuclear forensics science, the samples were solid, pure UO₂ or U₃O₈ particles. The precision achieved using TIMS analysis was 0.04%, which is similar or even better than the one obtained using the SIMS technique (0.05%), and clearly better if compared to that of GDMS (0.5%). The samples used by TIMS are micrograms in size. The suitability of TIMS as a n(¹⁸O)/n(¹⁶O) measurement method is verified by SIMS measurements. In addition, TIMS results have been confirmed by characterizing the n(¹⁸O)/n(¹⁶O) ratio of UO₂ sample also by the traditional method of static vacuum mass spectrometry at the University of Chicago.     

Rapid separation and purification of uranium and plutonium from dilute-matrix samples

This work describes a streamlined approach to the separation and purification of trace uranium and plutonium in environmental swipe samples that contain a small amount of collected bulk material. We describe key modifications to conventional techniques that result in a relatively rapid, safe, cost-effective, and efficient U and Pu separation process. Simulated samples were produced by loading appropriate ²³⁵U, ²³⁸U, and ²⁴⁰Pu onto high purity cotton swipes. Uranium concentration and isotopic composition were measured by multi-collector inductively coupled mass spectrometry. Corresponding plutonium measurements were conducted with a three stage thermal ionization mass spectrometer. Quantitative U and Pu recoveries were observed with this method.     

Role of alkyl substituent in room temperature ionic liquid on the electrochemical behavior of uranium ion and its local environment

A systematic study was carried out to understand the effect of structural modification of C_nmim⁺ moiety of C_nmimBr (n = 6, 8 or 10) on the electrochemical behavior of uranium. The cyclic voltammetric study of the above room-temperature ionic liquids (RTIL) media revealed that with increase in the chain length the electrochemical window extended more towards the negative potential. This resulted in the possibility of conversion of U(VI) to U(III) or even possibly to, U metal via U(IV) (as UO₂) when n ≥ 10. The diffusion coefficient of U(VI) was found to decrease from n = 6 to 8 to 10 due to the increasing order of viscosity of the RTIL. As a consequence, the activation energy was found to follow reverse order i.e. E _act(C₆mimBr) < E _act(C₈mimBr) < E _act(C₁₀mimBr). The conversion of UO₂ ²⁺ to UO₂ was found to be quasi reversible and also exothermic while the entropy was found to decrease due to the reduction reaction. An UV–Vis spectroscopic study was also carried out to understand the local environment around uranium in aqueous and RTIL media. Among several cationic and anionic species, the predominance of UO₂Cl₄ ^2? in 7 M HCl with D_4h coordination symmetry was observed. The decrease in symmetric stretching frequency of UO₂ ²⁺ in RTILs in comparison with aqueous system indicates that the bond strength of UO₂ ²⁺ in aqueous is less than that of UO₂ ²⁺ in RTILs.     

Performance of laser ablation: quadrupole-based ICP-MS coupling for the analysis of single micrometric uranium particles

In this paper we describe the application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) coupling to particle analysis, i.e., the determination of the isotopic composition of micrometric uranium particles. The performances of this analysis technique are compared with those of the two reference particle analysis techniques: secondary ion mass spectrometry (SIMS) and fission track-thermo-ionization mass spectrometry (FT-TIMS), based on the measurement of the isotopic ratios of ²³⁵U/²³⁸U in particles present in an inter-comparison particulate sample. The agreement of the results obtained using LA-ICP-MS with target values and with the results obtained using FT-TIMS and SIMS was good. Accuracy was equivalent to that of the other two techniques (±3 % deviation). However, relative experimental uncertainties present with LA-ICP-MS (7 %) were higher than those present with FT-TIMS (4.5 %) and SIMS (3 %). Furthermore, measurement yield of LA-ICP-MS coupling was close to that obtained with the same quadrupole ICP-MS for the measurement of a liquid sample (~10^?4), but lower than that obtained with FT-TIMS and SIMS, respectively, by a factor of 10 and 20, although the particles analyzed using LA-ICP-MS were most likely smaller (diameter ~0.6 μm, containing 4–7 fg of ²³⁵U). Nevertheless, thanks to the brevity of the signals obtained, the detection capacity for low isotopic concentrations by LA-ICP-MS coupling is equivalent to that of FT-TIMS, although it remains well below that of SIMS (×15). However, with more sensitive double focusing ICP-MS, performances equivalent to those achieved using SIMS could be obtained.     

Fission track–secondary ion mass spectrometry as a tool for detecting the isotopic signature of individual uranium containing particles

A fission track technique was used as a sample preparation method for subsequent isotope abundance ratio analysis of individual uranium containing particles with secondary ion mass spectrometry (SIMS) to measure the particles with higher enriched uranium efficiently. A polycarbonate film containing particles was irradiated with thermal neutrons and etched with 6 M NaOH solution. Each uranium containing particle was then identified by observing fission tracks created and a portion of the film having a uranium containing particle was cut out and put onto a glassy carbon planchet. The polycarbonate film, which gave the increases of background signals on the uranium mass region in SIMS analysis, was removed by plasma ashing with 200 W for 20 min. In the analysis of swipe samples having particles containing natural (NBL CRM 950a) or low enriched uranium (NBL CRM U100) with the fission track–SIMS method, uranium isotope abundance ratios were successfully determined. This method was then applied to the analysis of a real inspection swipe sample taken at a nuclear facility. As a consequence, the range of ²³⁵U/²³⁸U isotope abundance ratio between 0.0276 and 0.0438 was obtained, which was higher than that measured by SIMS without using a fission track technique (0.0225 and 0.0341). This indicates that the fission track–SIMS method is a powerful tool to identify the particle with higher enriched uranium in environmental samples efficiently.     

Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore

In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (µ ^max) and doubling time (t _d) were obtained 0.08 h^?1 and 8.66 h, respectively. Parameters such as Fe²⁺ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 ± 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 °C in 48 h with the particles of d ₈₀ = 100 μm. The optimum concentration of supplementary Fe²⁺ was dependent to the PD. This value was 0 and 10 g of FeSO₄·7H₂O/l at the PD of 5 and 15 %, respectively. The effects of time, pH and PD on the bioleaching process were studied using central composite design. New rate equation was improved for the uranium leaching rate. The rate of leaching is controlled with the concentrations of ferric and ferrous ions in solution. This study shows that uranium bioleaching may be an important process for the Saghand U mine at Yazd (Iran).     

Determination of Hg isotopic compositions in certified reference material NIES No. 13 Human Hair by cold vapor generation multi-collector inductively coupled plasma mass spectrometry

Hg isotopic ratios of NIES CRM No. 13 Human Hair were analyzed using cold vapor generation coupled to multi-collector inductively coupled plasma mass spectrometer to meet the growing demand for better understanding of Hg exposure routes by using Hg isotopic compositions in human hair samples. To validate and assure the accuracy of our analytical method, (1) the reproducibility of the Hg isotopic measurement was monitored and (2) the Hg isotopic compositions of four secondary reference materials—IAEA-085, IAEA-086, and CRPG-RL24H—were measured. Our results for NIES CRM No. 13 show the mass-dependent fractionation values of δ ¹⁹⁹Hg = (2.13 ± 0.07) ‰, δ ²⁰⁰Hg = (0.98 ± 0.08) ‰, δ ²⁰¹Hg = (2.77 ± 0.10) ‰, δ ²⁰²Hg = (1.89 ± 0.10) ‰, and δ ²⁰⁴Hg = (2.76 ± 0.16) ‰ (2SD, n = 11) and the mass-independent fractionation values of Δ ¹⁹⁹Hg = (1.65 ± 0.06) ‰, Δ ²⁰⁰Hg = (0.04 ± 0.04) ‰, Δ ²⁰¹Hg = (1.36 ± 0.07) ‰, and Δ ²⁰⁴Hg = (?0.04 ± 0.11) ‰ (2SD, n = 11). Interlaboratory comparison of the CRM performed at the University of Pau showed good agreement with the values obtained at NIES.