Colloidal transport of uranium in soil: Size fractionation and characterization by field-flow fractionation–multi-detection

The aim of this study was to characterize colloids associated with uranium by using an on-line fractionation/multi-detection technique based on asymmetrical flow field-flow fractionation (As-Fl-FFF) hyphenated with UV detector, multi angle laser light scattering (MALLS) and inductively coupling plasma-mass spectrometry (ICP-MS). Moreover, thanks to the As-Fl-FFF, the different colloidal fractions were collected and characterized by a total organic carbon analyzer (TOC). Thus it is possible to determine the nature (organic or inorganic colloids), molar mass, size (gyration and hydrodynamic radii) and quantitative uranium distribution over the whole colloidal phase. In the case of the site studied, two populations are highlighted. The first population corresponds to humic-like substances with a molar mass of (1500 ± 300) g mol⁻¹ and a hydrodynamic diameter of (2.0 ± 0.2) nm. The second one has been identified as a mix of carbonated nanoparticles or clays with organic particles (aggregates and/or coating of the inorganic particles) with a size range hydrodynamic diameter between 30 and 450 nm. Each population is implied in the colloidal transport of uranium: maximum 1% of the uranium content in soil leachate is transported by the colloids in the site studied, according to the depth in the soil. Indeed, humic substances are the main responsible of this transport in sub-surface conditions whereas nanoparticles drive the phenomenon in depth conditions.     

Uranium colloid analysis by single particle inductively coupled plasma-mass spectrometry

Uranium single particle analysis has been performed by inductively coupled plasma-mass spectrometry (ICP-MS) and the performances are compared with that provided by scanning electron microsopy and single particle counting. The transient signal induced by the flash of ions due to the ionisation of an uranium colloidal particle in the plasma torch can be detected and measured for selected uranium ion masses (²³⁸U⁺, ²³⁵U⁺ or ²⁵⁴[²³⁸U¹⁶O]⁺) by the mass spectrometer. The signals recorded via time scanning are analysed as a function of particle size or fraction of the studied element or isotope in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. The feasibility tests were performed on uranium dioxide particles. The study also describes the experimental conditions and the choice of mass to detect uranium colloids in a single particle analysis mode.     

Comparison of ICP-MS and SIMS techniques for determining uranium isotope ratios in individual particles

The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 μm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.     

Characterisation of River Po particles by sedimentation field-flow fractionation coupled to GFAAS and ICP-MS

A procedure for elemental composition determination of water-borne river particles (Po River) on both size-fractionated and unfractionated submicron particles (0.1–1 μm) by graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma-mass spectrometry (ICP-MS) is reported. Sample fractionation was performed using sedimentation field-flow fractionation (SdFFF). The distribution of relative mass vs. particle size was determined using UV detection. Fractions were collected over a narrow size range for scanning electron microscopy. With this combination of techniques the mass, elemental composition, and shape distributions can be obtained across the size spectrum of the sample.

The size distributions of the major elements (Al, Fe) were determined by coupling both GFAAS and ICP-MS techniques to the SdFFF. The procedure was validated using a reference clay sample. Satisfactory agreement was found between both the GFAAS and ICP-MS aluminium signal and the UV detector signal. Some discrepancies were observed in the Fe/Al ratios when comparing GFAAS and ICP-MS. Thus further investigation is in order to fully assess the role of SdFFF-ICP-MS and SdFFF-GFAAS techniques for elemental characterisation of aquatic colloids. Both GFAAS and ICP-MS signals unambiguously indicate a significantly higher Fe content in the lower size range, which is consistent with previous investigations.

Trace element levels in unfractionated Po River particles, determined by both GFAAS and ICP-MS, show good agreement. The high levels of Cu, Pb, Cr and Cd found associated with the colloidal particles underlines the significance of the environmental role played by the suspended matter in rivers in both highly industrialised and intensively cultivated areas.     

Determination of 237Np and Pu isotopes in large soil samples by inductively coupled plasma mass spectrometry

A new method for the determination of (237)Np and Pu isotopes in large soil samples has been developed that provides enhanced uranium removal to facilitate assay by inductively coupled plasma mass spectrometry (ICP-MS). This method allows rapid preconcentration and separation of plutonium and neptunium in large soil samples for the measurement of (237)Np and Pu isotopes by ICP-MS. (238)U can interfere with (239)Pu measurement by ICP-MS as (238)UH(+) mass overlap and (237)Np via (238)U peak tailing. The method provides enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then transferring Pu to DGA resin for additional purification. The decontamination factor for removal of uranium from plutonium for this method is greater than 1×10(6). Alpha spectrometry can also be applied so that the shorter-lived (238)Pu isotope can be measured successfully. (239) Pu, (242)Pu and (237)Np were measured by ICP-MS, while (236)Pu and (238)Pu were measured by alpha spectrometry.     

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 x 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 x 10(-4) and 1.4 x 10(-4), respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 microg 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/P38U) 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, alpha- and gamma-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.     

煤中碘的淋滤行为研究

用不同pH值溶液对煤进行动态淋滤实验,用电感耦合等离子体质谱(ICP-MS)测定不同pH值淋滤液在不同时间段获取的淋出液中碘的浓度,以及煤和淋滤后残留煤的高温热水解溶液中碘的含量。结果表明,淋滤液pH值、淋滤时间、煤中碘的赋存形态及在煤中的赋存部位对碘的淋出有重要影响。淋滤液的酸性越强,煤中碘的淋出越多,pH值为2.0和pH值为4.0溶液对煤中碘的淋出率(η)分别为7.22%和6.20%;但pH值为2.0溶液的淋出液中碘的量小于pH值为4.0溶液的淋出液中碘的量,其百分率(w_x)分别为1.920 0%和5.420 0%。pH 2.0淋滤液,在前30 h内淋出液中碘的平均浓度为10.9 μg/L;而pH值为4.0淋滤液,在前110 h内淋出液中碘的平均浓度为10.6 μg/L;pH值为6.0和pH值为7.5溶液能淋出煤中碘很少。在酸性溶液作用下,首先被淋出的碘是存在煤颗粒表面少量的水溶态和离子交换态碘及大部分碳酸盐态和铁锰氧化物结合态碘,然后煤基质内部的部分水溶态和离子交换态碘及少量的碳酸盐结合态及铁锰氧化物结合态碘等才被淋出。     

Selenium speciation analysis in a sediment using strong anion exchange and reversed phase chromatography coupled with inductively coupled plasma-mass spectrometry

An analytical procedure for selenium speciation of analysis of selenourea (SeU), selenoethionine (SeE), selenomethionine (SeM), Se(VI), Se(IV), dimethylselenide (dMeSe) and dimethyldiselenide (dMedSe) was developed, based on two complementary liquid chromatography (LC) techniques coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Specifically, strong anion exchange (SAX) chromatography coupled with ICP-MS was used for the separation and quantification of all the earlier mentioned Se compounds, except for the two methyl selenides, which could be separated and determined by reversed phase chromatography coupled with ICP-MS. This procedure was applied to a soil sample from the warm springs area of Thermopyles (Greece). For leaching the Se species from the soil sample, four extraction methods, using water at ambient temperature, hot water, methanol and 0.5 M HCl, were tested for their efficiency of extracting the different Se species. The speciation results obtained by the LC-ICP-MS methods were compared with those obtained by voltammetric techniques. The determination of total selenium in the sample was achieved by graphite furnace atomic absorption spectrometry, as well as by ICP-atomic emission spectrometry, after suitable digestion of the sediment sample.     

Use of chromatographic pre-concentration for routine uranium bioassay analysis by ICP-MS

Routine monitoring of urine is an effective way to detect occupational intake of radioactive material. Historically, determinations of uranium isotopic ratios have been performed by radiochemical separation followed by alpha spectrometry. With recent advancements in technology, inductively coupled plasma-mass spectrometry (ICP-MS) has become widely available for the determination of trace metals as well as radioactive nuclides with long half-lives, such as ²³⁸U in urine. Furthermore, ICP-MS measurements of ²³⁸U do not require radiochemical separation since the number of atoms in the sample is determined instead of the number of alpha particles emitted. However, this method does not provide good sensitivity for the determination of ²³⁵U due to its shorter half-life. An improved procedure using pre-concentration of uranium and determination by ICP-MS decreases the detection limit by a factor of ten or greater with only slight increase in total analysis time. The method also has the capability of accurately determining the isotopic ratio of the sample, which is very important in cases where enriched or depleted uranium is involved.     

逆流色谱分离感应耦合等离子质谱在线测量超痕量钚

将逆流色谱（CCC）与感应耦合等离子质谱（ICP-MS）相联,研究了几种两相体系在CCC中的固定相保留率,从中选择1％TNOA-正庚烷作固定相,通过CCC富集分离钚并去除基体及干扰元素,通过研究在线分离条件及定量方法等,建成了CCC分离ICP—MS在线测量超痕量钚的方法。采用该方法分析得到实际土壤样品中^239Pu的含量与由传统的分离方法给出的结果相吻合。     

Determination of uranium in tap water by ICP-MS

A fast and accurate procedure has been developed for the determination of uranium at microg L(-1) level in tap and mineral water. The method is based on the direct introduction of samples, without any chemical pre-treatment, into an inductively coupled plasma mass spectrometer (ICP-MS). Uranium was determined at the mass number 238 using Rh as internal standard. The method provides a limit of detection of 2 ng L(-1) and a good repeatability with relative standard deviation values (RSD) about 3% for five independent analyses of samples containing 73 microg L(-1) of uranium. Recovery percentage values found for the determination of uranium in spiked natural samples varied between 91% and 106%. Results obtained are comparable with those found by radiochemical methods for natural samples and of the same order for the certified content of a reference material, thus indicating the accuracy of the ICP-MS procedure without the need of using isotope dilution. A series of mineral and tap waters from different parts of Spain and Morocco were analysed.     

Comparison of NAA and ICP-MS for the determination of major and trace elements in environmental sample

Summary Major and trace elements in soil and plant samples, including standard reference materials were determined by means of neutron activation analysis (NAA) and inductively coupled plasma-mass spectrometry (ICP-MS). The analytical procedure for NAA utilized dried powder samples. The concentration of iodine in soil samples was determined by radiochemical NAA. The irradiated samples were cooled and then counted with a Ge gamma-ray detector connected to a multi-channel analyzer. For ICP-MS analysis, the samples were decomposed by microwave digestion with an acid mixture. The concentration of I in the soil samples was measured by ICP-MS after separation by ignition. The analytical values for most elements in the environmental samples by both methods were in good agreement, whereas sample treatments were different. Measured value of Zr in the soil samples by ICP-MS was about 50% lower than that by NAA. It should be assumed that some minerals of Zr in soil particles were not entirely dissolved by the acid mixture. Analytical results of Cd for three different Cd levels in unpolished rice flour samples (NIES 10-a, b and c) determined by ICP-MS were in agreement with certified values. The concentration of Cd in the sample with the lowest Cd level, as determined by NAA with 57% counting error, was 3 times higher than the certified value.     

Thorium colloid analysis by single particle inductively coupled plasma-mass spectrometry

Thorium colloid analysis in water has been carried out by a single particle mode using inductively coupled plasma mass spectrometry (ICP-MS). The flash of ions due to the ionisation of a thorium colloidal particle in the plasma torch can be detected and measured in a time scan for ²³²Th⁺ or ²⁴⁸[ThO]⁺ according to the sensitivity required by the mass spectrometer. The peaks of the recorded intensity of the MS signal can be analysed as a function of the particle size or fraction of the studied element in the colloid phase. The frequency of the flashes is directly proportional to the concentration of particles in the colloidal suspension. After discussing Th colloid detection, on the basis of the intensity of the ion flashes generated in the plasma torch, tests were performed on thorium dioxide colloidal particles. This feasibility study also describes the experimental conditions and the limitation of the plasma design to detect thorium colloids in a single particle analysis mode down to about 10 fg.     

Separation of uranium from uraniferous coaly clays using a selective ion-exchange two-step elution system

Summary An ion-exchange process for the selective separation and enrichment of uranium from the main elements Si, Al, Fe, Ca, Mg, Na, K as well as from Mo and V, which are present in uraniferous coaly clays, has been developed. After a selective carbonate leaching of the roasted ore, a 0.5 mol/l Na₂CO₃/0.5 mol/l NaHCO₃ solution was passed through the macroporous ion-exchanger AG MP-1, which at pH10 absorbed uranium quantitatively in form of a carbonato complex. Remaining absorbed amounts of Mo and V were eluted with 0.1 mol/l EDTA in 0.5 mol/l Na₂CO₃/0.5 mol/l NaHCO₃, while U was quantitatively separated by a second elution step with 0.5 mol/l HNO₃ and was afterwards precipitated with NH₄OH as a high-grade yellow cake. Differential pulse polarography (DPP), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS) had been used to determine the uranium content in the raw materials and to investigate the effectivity of the different steps of the developed process.     

Isotopic analysis of single uranium and plutonium particles by chemical treatment and mass spectrometry

The isotopic composition of single uranium and plutonium particles was measured with an inductively coupled plasma mass spectrometer (ICP-MS) and a thermal ionization mass spectrometer (TIMS). Particles deposited on a carbon planchet were first analyzed with an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope (SEM) and then transferred on to a silicon wafer using a manipulator. The particle on the silicon wafer was dissolved with nitric acid and the isotopic ratios of U and Pu were measured with ICP-MS and TIMS. The results obtained by both methods for particles of certified reference materials showed good agreement with the certified values within the expected uncertainty. The measurement uncertainties obtained in this study were similar for both mass spectrometric methods. This study was performed to establish the method of particle analysis with SEM, EDX, the particle manipulation and chemical preparation technique, and the measurement of isotopic ratios of U and Pu in a single particle by mass spectrometry.     

Analytical methods for the environmental quantification of uranium isotopes: Method of validation and environmental application

The use of depleted uranium in military ordinance has led to an increasing need to determine isotope-specific uranium concentrations in environmental matrices. To this end, gamma-ray spectrometry, ICP-MS and INAA methods have been validated, in accordance with the ISO 17025 standard. Reporting limits of 0.21 (U-235) and 0.91 (U-238) ng/L were obtained by ICP-MS analysis of water. Higher reporting limits were obtained for INAA (U-238 only) validations of water and gamma-ray spectrometric validations of soil and water. Accredited methods have been used to determine uranium concentration and isotope ratio of samples obtained from the Defence Research and Development Canada Valcartier, Quebec.     

Adsorbed compounds on pine needle surfaces for the environmental monitoring of uranium

In order to examine the feasibility of the adsorbed compounds on the pine needles for environmental monitoring of uranium, the adsorbed compounds were recovered by solvent washing, and the elemental concentrations in the compounds were compared with those of air particles and pine needles. It was found, that the concentration patterns of elements in the compounds corresponded to those of air particles, which meant that the air particles were the main components of the compounds. The analysis by ICP-MS suggested that the uranium in the compounds has a natural composition. Therefore, the adsorbed compounds to the pine needles can be considered as potential indicators for the environmental monitoring of uranium.     

Precise and accurate isotope ratio measurements by ICP-MS

The precise and accurate determination of isotope ratios by inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) is important for quite different application fields (e.g. for isotope ratio measurements of stable isotopes in nature, especially for the investigation of isotope variation in nature or age dating, for determining isotope ratios of radiogenic elements in the nuclear industry, quality assurance of fuel material, for reprocessing plants, nuclear material accounting and radioactive waste control, for tracer experiments using stable isotopes or long-lived radionuclides in biological or medical studies). Thermal ionization mass spectrometry (TIMS), which used to be the dominant analytical technique for precise isotope ratio measurements, is being increasingly replaced for isotope ratio measurements by ICP-MS due to its excellent sensitivity, precision and good accuracy. Instrumental progress in ICP-MS was achieved by the introduction of the collision cell interface in order to dissociate many disturbing argon-based molecular ions, thermalize the ions and neutralize the disturbing argon ions of plasma gas (Ar+). The application of the collision cell in ICP-QMS results in a higher ion transmission, improved sensitivity and better precision of isotope ratio measurements compared to quadrupole ICP-MS without the collision cell [e.g., for 235U/238U approximately 1 (10 microg x L(-1) uranium) 0.07% relative standard deviation (RSD) vs. 0.2% RSD in short-term measurements (n = 5)]. A significant instrumental improvement for ICP-MS is the multicollector device (MC-ICP-MS) in order to obtain a better precision of isotope ratio measurements (with a precision of up to 0.002%, RSD). CE- and HPLC-ICP-MS are used for the separation of isobaric interferences of long-lived radionuclides and stable isotopes by determination of spallation nuclide abundances in an irradiated tantalum target.     

Determination of rare earth elements, thorium and uranium by inductively coupled plasma mass spectrometry and strontium isotopes by thermal ionization mass spectrometry in soil samples of Bryansk region contaminated due to Chernobyl accident

The present paper describes the inductively coupled plasma mass spectrometric (ICP-MS) determination of rare earth elements (REEs), thorium and uranium in forest, pasture, field and kitchen garden soils from a Russian territory and in certified reference materials (JLK-1, JSD-2 and BCR-1). In addition to concentration data, strontium isotopic composition of the soil samples were measured by thermal ionization mass spectrometry. The measurements contributed to the understanding of the background levels of these elements in an area contaminated due to Chernobyl accident. There was not a significant variation in the concentration of REEs at different depth levels in forest soil samples, however, the ratio of Th/U varied from 3.32 to 3.60. Though concentration of U and Th varied to some extent, the ratio did not show much variation. The value of ⁸⁷Sr/⁸⁶Sr ratio, was in the top layer soil sample relatively higher than in the lower layers.     

Development of an integrated flow injection system for the electro-oxidative leaching of uranium from geological samples and its spectrophotometric determination with Arsenazo III

This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric determination of uranium in ore samples. By associating a conventional flow injection system, used for uranium determination with Arsenazo III, with an on-line system for electro-oxidative leaching, a fully integrated system was assembled. The systems were integrated after achieving optimum conditions for uranium determination and leaching. According to the results obtained in the present work, a current density of 280 mA cm⁻² generated enough hypochlorite ions in the electrolyte solution (3.6 mol L⁻¹ HCl + 2% (w/v) NaCl) to promote quantitative oxidation of U(IV) to U(VI) thus improving the extraction efficiency. The slurry density did not significantly affect the performance of the system and the increasing temperature resulted in a decrease in extraction efficiency. This methodology was applied in the determination of U₃O₈ in four ore samples and the results obtained agreed with those obtained by ICP-MS after conventional wet acid digestion of the samples.