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.     

The determination of natural uranium in human tissues by recovery corrected kinetic phosphorescence analysis

Two typical methods used for the determination of uranium in human autopsy tissues are kinetic phosphorescence analysis (KPA) and alpha-spectrometry, both of which have significant limitations and advantages. KPA is limited because of the amount of sample used (1–10 ml for sample digestion followed by one ml KPA aliquots), no isotopic information is provided, phosphorescence degradation by salts in solution, and even more importantly, it does not provide chemical recovery information. For samples with sub ng uranium concentrations per g of inorganic material, preconcentration is necessary, which may require chemical recovery (other than simple evaporation). While alpha-spectrometry has very good radiometric detection limits for ²³⁸U, the very long half-life of ²³⁸U (4.468·10⁹ y) restricts its mass detection limit (27 ng). KPA, on the other hand, has a detection limit three orders of magnitude lower (0.02 ng) for natural uranium. A recovery corrected method for the determination of natural uranium in human tissues was developed combining preconcentration of human tissues dissolved in 6M HCl by anion exchange with alpha-spectrometry and kinetic phosphorescence analysis, utilizing ²³²U as a tracer. Solution aliquots containing up to 6 g of bone ash were pre-concentrated for KPA measurement thereby allowing the use of up to 25% of the original sample solution weight for analysis by KPA. The radiochemical yield of ²³²U was determined by alpha-spectrometry and the uranium content was determined by KPA. The mean radiochemical yields obtained for human tissue samples range from 65% to 106% with a mean of 85%±8%.     

Activity disequilibrium between 234U and 238U isotopes in natural environment

The aim of this work was to calculate the values of the ²³⁴U/²³⁸U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wi?linka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the ²³⁴U/²³⁸U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the ²³⁴U/²³⁸U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the ²³⁴U/²³⁸U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wi?linka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes ²³⁴U and ²³⁸U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the ²³⁴U/²³⁸U activity ratio really oscillates around unity.     

Determination of234U/238U and235U/238U ratios from commercially available uranium compounds by α-spectrometry

The²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios from uranium compounds by -spectrometry technique have been obtained. Ten commercially available uranium reagents were analyzed. The well-separated peaks corresponding to uranium isotopes are evident, providing an energy spectrum of the -particles of uranium isotopes. It was found that some commerical uranium salts were depleted in²³⁴U and²³⁵U.     

Reagent grade uranium salts: Isotopic composition by neutron activation

A rapid non-destructive neutron activation technique for the determination of the²³⁸U/²³⁵U ratio is described. Reagent grade uranium salts from commercial sources have a widely variable²³⁸U/²³⁵U ratio. The isotopic composition of uranium found in such salts is quite different from the natural value. This difference is largely due to the use of by-product uranium depleted in²³⁵U.     

A new radiochemical procedure for uranium assay in environmental samples

A new and economical method for assay of environmental samples for uranium isotopes is proposed. Separation and radiochemical purification of uranium isotopes (²³⁴U,²³⁵U and²³⁸U) from other elements is achieved on a single anion exchange column by washing with various concentrations of hydrochloric acid. Iron, the principal interfering element is removed from the colum by washing with 4.5M hydrochloric acid with a combination of reducing agents under the conditions described. Weightless samples of uranium are prepared by either evaporation in a polished stainless steel dish or electroplated on a stainless steel planchet. This method is applicable for air particulates, soils, sediments, coal, water, vegetation, and biologicals. Text of the paper presented in the symposium on Practical Applications of Nuclear and Radiochemistry, at Las Vegas, Nevada, August 25–29, 1980. Submitted for publication in Advances in Chemistry Series.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Isotopic uranium analysis in urine samples by alpha spectrometry

Urine assay is the preferred method for monitoring accidental or chronic internal intake of uranium into the human body. A new radiochemical separation procedure has been developed to provide isotopic uranium analysis in urine samples. In the procedure, uranium is co-precipitated with hydrous titanium oxide (HTiO) from urine matrix, and is then purified by anion exchange chromatographic column. Alpha spectrometry is used for isotopic uranium analysis after preparation of a thin-layer counting source by cerium fluoride micro-precipitation. Replicate spike and procedural blank samples were prepared and measured to validate the procedure. The ²³²U tracer was utilized for chemical recovery correction, and an average recovery of 76.2 ± 8.1% was found for 1400 mL urine samples. With 48 h of counting, the minimum detectable activity concentrations were determined to be 0.43, 0.21 and 0.42 mBq/L for ²³⁸U, ²³⁵U and ²³⁴U, respectively.     

Uranium in natural waters sampled within former uranium mining sites in Kazakhstan and Kyrgyzstan

New data are presented on ²³⁸U concentrations in surface and ground waters sampled at selected uranium mining sites in Kazakhstan and Kyrgyzstan and in water supplies of settlements located in the vicinity of these sites. Radiochemical neutron activation analysis (RNAA) was used for ²³⁸U determination in all cases. In addition, for data accuracy assessments purposes, a sub-set of these samples was analysed by high-resolution alpha spectrometry, following standard radiochemical separation and purification. Our data show that drinking waters sampled at various settlements located close to the uranium mining sites are characterised by relatively low uranium concentrations (1.9–35.9 μg L⁻¹) compared to surface waters sampled within the same sites. The latter show high concentrations of total uranium, reflecting the influence from the radioactive waste generated as a result of uranium ore production.     

Distribution of uranium in sediment of creek ecosystem

The present study was carried on distribution of uranium isotopes and Thorium in marine sediment from creek of Mumbai Harbour Bay (MHB) using radiochemical separation followed by alpha spectrometry. The activity concentration of uranium and thorium in sediment of MHB has ranged between 1–4 and 1.8–4.5 ppm respectively. The activity ratio of ²³⁴U/²³⁸U in sediment was found close to unity at most of the locations of creek suggesting a conservative behaviour. The observed Th/U ratio (0.9) in comparison to global Th/U ratio (?3.5) in the creek sediment indicates that it receives low radiogenic nature of terronenous input.     

Uranium analysis in urine by inductively coupled plasma dynamic reaction cell mass spectrometry

Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of ²³⁵U/²³⁸U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uraniums ²³⁵U/²³⁸U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the ²³⁵U/²³⁸U ratio. The quantitative analysis was achieved using ²³³U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized ²³⁵U⁺ and ²³⁸U⁺ into ²³⁵UO₂⁺ (m/z=267) and ²³⁸UO₂⁺ (m/z=270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the ²³⁵U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL^–1 urine and an average coefficient of variation (CV) of 1–2% within the sample measurements. The method detection limit for determining ²³⁵U/²³⁸U ratio was 3.0 pg U mL^–1 urine. An additional 21 patient samples were analyzed with no information about medical history. The measured ²³⁵U/²³⁸U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.The opinions and assertions expressed herein are those of the authors and are not to be construed as official or as representing the views of the Armed Forces Institute of Pathology, the Department of the Army, or the Department of Defense     

Isotopic analysis of uranium in NIST SRM glass by femtosecond laser ablation MC-ICPMS

We employed femtosecond Laser Ablation Multicollector Inductively Coupled Mass Spectrometry for the determination of uranium isotope ratios in a series of standard reference material glasses (NIST 610, 612, 614, and 616). The uranium in this series of SRM glasses is a combination of isotopically natural uranium in the materials used to make the glass matrix and isotopically depleted uranium added to increase the uranium elemental concentration across the series. Results for NIST 610 are in excellent agreement with literature values. However, other than atom percent ²³⁵U, little information is available for the remaining glasses. We present atom percent and isotope ratios for ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U for all four glasses. Our results show deviations from the certificate values for the atom percent ²³⁵U, indicating the need for further examination of the uranium isotopes in NIST 610-616.     

Simultaneous analysis of uranium and plutonium using thermal ionization mass spectrometry

Simultaneous isotopic analysis of uranium and plutonium using thermal ionization mass spectrometer coupled to a multi-collector detection assembly with 9 Faraday cups has been reported earlier. Subsequently investigations have been carried out (1) to understand the applicability of correction methodologies available to account for the contribution of²³⁸Pu at²³⁸U and (2) to evaluate the effectiveness of these methodologies on the accuracy of²³⁵U/²³⁸U atom ratio being determined, particularly when samples containing different U/Pu atom ratios. Isotopic fractionation for both U and Pu in the simultaneous isotopic analysis has been compared with the results of the individual analysis of these elements. The different isotopic fractionation factors observed for U were attributed to different conditions of analysis. There was no significant difference in the isotopic fractionation patterns for Pu. The consideration to extend this method to actual samples from our observations on synthetic samples with diferent U/Pu atom ratios containing U and Pu isotopic reference standards is described.     

The determination of235U/238U ratios by activation analysis utilizing high resolution γ-spectrometry

The application of high resolution γ-spectrometry to the direct determination of²³⁵U/²³⁸U isotopic ratios in small uranium samples after neutron activation is reported. The consistency obtained relative to mass spectrometrically determined isotopic ratios is better than 5% for isotopic ratios between 0.06885 and 1.095. The method is not subject to the main disadvantages of the known radiochemical methods for²³⁵U/²³⁸U isotopic ratio determinations, and should be appreciably more rapid compared to the solid-source mass spectrometric method giving the same precision.     

Cross sections of barium isotopes in the interaction of 60 MeV/nucleon 18O with 238U

Barium isotopes were produced by 60 MeV/u ¹⁸O ion bombardment of natural uranium via ²³⁸U (¹⁸O, X) reactions. Ba sources were prepared by radiochemical separation, and measured by a HPGe detector. The cumulative cross sections were obtained by analysis of measured time sequence g-ray spectra. A double peak phenomenon in Ba isotope distribution was observed.     

The microenvironment of iron in (Ba,Ca)(Fe,Co)O3−δ catalyst system: A Mössbauer study

Undisturbed, non-fertilized woodland soil (“loamy sandy soil” type) from 1 m below surface was dry and wet sieved. Sieving fractions of <10–1000 μm were analyzed for total alpha-activity. Thorium and uranium contents were determined by alpha-spectrometry after radiochemical separation. Soluble and insoluble parts of thorium and uranium were determined in the sieved fractions indicating that the isotope distribution in soil correlates with the particle size distribution: The smaller the size fraction the higher the isotope content. Isotope ratios of²²⁸Th/²³²Th, and²³⁴U/²³⁸U are discussed.     

Concentration, distribution and characteristics of depleted uranium (DU) in the Kosovo ecosystem: A comparison with the uranium behavior in the environment uncontaminated by DU

The smear samples of the penetrator were analyzed for the determination of the uranium composition. The obtained relative composition (m/m) of uranium isotopes in all the smear samples is in the range of 99.76-99.78% for ²³⁸U, 0.000659-0.000696% for ²³⁴U, 0.213-0.234% for ²³⁵U, and 0.00274-0.00328% for ²³⁶U, showing characteristics of depleted uranium (DU). The uranium concentrations in Kosovo soil and water samples as well as biological samples were investigated. It was found that the uranium concentrations in the Kosovo soil samples are in the range of 11.3-2.26·10⁵ Bq·kg^-1 for ²³⁸U, 10.3-3.01·10⁴ Bq·kg^-1 for ²³⁴U, 0.60-3251 Bq·kg^-1 for ²³⁵U, and ￡0.019-1309 Bq·kg^-1 for ²³⁶U. The obtained activity ratios are in the range of 0.112-1.086 for ²³⁴U/²³⁸U, 0.0123-0.1144 for ²³⁵U/²³⁸U, and 0-0.0078 for ²³⁶U/²³⁸U, indicating the presence of DU in about 77% of the surface soil samples. At a specific site, the DU inventory in the surface soil is about 140 mg·cm^-2, which is 1.68·10⁶ times higher as the estimated mean DU dispersion rate in the region. The uranium concentrations in Kosovo lichen, mushroom, bark, etc., are in the range of 1.97-4.06·10⁴ Bq·kg^-1 for ²³⁸U, 0.48-5158 Bq·kg^-1 for ²³⁴U, 0.032-617 Bq·kg^-1 for ²³⁵U, and ￡0.019-235 Bq·kg^-1 for ²³⁶U with mean activity ratios of 0.325±0.0223 for ²³⁴U/²³⁸U, of 0.0238±0.0122 for ²³⁵U/²³⁸U, and 0.0034±0.0028 for +U/²³⁸U, indicating the presence of DU in the entire sample. On the contrary, the uranium concentrations in Kosovo water samples are low, compared with the water samples collected in central Italy, indicating the presence of negligible amount of DU. The uranium isotopes in Kosovo waters do not constitute a risk of health at the present time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of U isotope ratios in sediments using ICP-QMS after sample cleanup with anion-exchange and extraction chromatography

The determination of uranium is important for environmental radioactivity monitoring, which investigates the releases of uranium from nuclear facilities and of naturally occurring radioactive materials by the coal, oil, natural gas, mineral, ore refining and phosphate fertilizer industries, and it is also important for studies on the biogeochemical behavior of uranium in the environment. In this paper, we describe a quadrupole ICP-MS (ICP-QMS)-based analytical procedure for the accurate determination of U isotope ratios (²³⁵U/²³⁸U atom ratio and ²³⁴U/²³⁸U activity ratio) in sediment samples. A two-stage sample cleanup using anion-exchange and TEVA extraction chromatography was employed in order to obtain accurate and precise ²³⁴U/²³⁸U activity ratios. The factors that affect the accuracy and precision of U isotope ratio analysis, such as detector dead time, abundance sensitivity, dwell time and mass bias were carefully evaluated and corrected. With natural U, a precision lower than 0.5% R.S.D. for ²³⁵U/²³⁸U atom ratio and lower than 2.0% R.S.D. for ²³⁴U/²³⁸U activity ratio was obtained with less than 90 ng uranium. The developed analytical method was validated using an ocean sediment reference material and applied to an investigation into the uranium isotopic compositions in a sediment core in a brackish lake in the vicinity of U-related nuclear facilities in Japan.     

Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the ²³⁰Th/²³⁴U ratio was calculated from the measured ratios of ²³⁰Th/²³⁴Th and ²³⁴U/²³⁸U and from calculated ²³⁴Th/²³⁸U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The ²³⁴U interference on ²³⁴Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause.

     

Characterization of uranium isotopic abundances in depleted uranium metal assay standard 115

Certified reference material (CRM) 115, Uranium (Depleted) Metal (Uranium Assay Standard), was analyzed using a TRITON Thermal Ionization Mass Spectrometer to characterize the uranium isotope-amount ratios. The certified ²³⁵U/²³⁸U “major” isotope-amount ratio of 0.0020337 (12) in CRM 115 was determined using the total evaporation (TE) and the modified total evaporation (MTE) analytical techniques. In the MTE method, the total evaporation process is interrupted on a regular basis to allow correction of background from peak tailing, internal calibration of the secondary electron multiplier detector versus the Faraday cups, peak-centering, and ion source re-focusing. For the “minor” ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratio measurements using MTE, precision and accuracy comparable to conventional analyses are achieved, without compromising the quality of the ²³⁵U/²³⁸U isotope-amount ratios. Characterized values of the ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratios in CRM 115 are 0.000007545 (10) and 0.000032213 (84), respectively. The ²³³U/²³⁸U isotope-amount ratio in CRM 115 is estimated to be <5 × 10^?9. The homogeneity of the CRM 115 materials is established through the absence of any statistically significant unit-to-unit variation in the uranium isotope-amount ratios. The measurements leading to the certification of uranium isotope-amount ratios are discussed.