Sequential Injection Method for Rapid and Simultaneous Determination of 236U, 237Np, and Pu Isotopes in Seawater

Comparison for the simultaneous determination of 237Np and Pu isotopes between TEVA and TK200 resin

A reliable and stable method was developed to accurately analyze neptunium (237Np) and plutonium isotopes in environmental samples using 242Pu or 236Pu as a tracer. Key parameters, including the valence adjustment conditions and the stabilities of Pu and Np in the different resins, were investigated using TK200 and TEVA resin. It was found that Pu and Np could be efficiently extracted simultaneously using TK200 resin under the optimal loading conditions (6-12 M HNO3) with the addition of 0.01-0.12 M NaNO2 for valence adjustment. These isotopes were subsequently stripped out using a solution containing 0.1 M HCl, 0.05 M HF, and 0.01 M NH2OH·HCl. The separation efficiencies of Pu and Np were >93%, and the chemical yield ratio between Np and Pu was maintained steady at an average of 1.00 ± 0.03 (n > 50) under the optimal conditions. The analytical method was validated by analyzing environmental soil samples spiked with known amounts of 239Pu and 237Np standard solutions or certified reference materials. The measured values of 237Np, 239Pu, and 240Pu obtained by inductively coupled plasma tandem mass spectrometry were consistent with their International Atomic Energy Agency literature values within a 95% confidence interval. These results confirm the reliability and high analytical precision (<6%) of this developed method using Pu as a non-isotopic tracer for monitoring the chemical yield of 237Np. The developed method can also be used for environmental pollutant monitoring and for tracer studies of the 237Np and Pu isotopes.

Rapid Method To Determine 137Cs, 237Np, and Pu Isotopes in Seawater by SF-ICP-MS

Neptunium-237, owing to its long half-life (t1/2 = 2.14 × 106 year) and similar conservatism to 137Cs, has the potential to replace 137Cs for water mass circulation studies on decades and even longer time scales. A new method for the determination of 137Cs, 237Np, and Pu isotopes in seawater samples was proposed to solve the difficulty of 237Np analysis in seawater. The developed method includes the separation technique of ammonium phosphomolybdate (AMP) adsorption for 137Cs and anion exchange chromatography for 237Np and Pu, a measurement technique of gamma spectrometry for 137Cs and SF-ICP-MS for 237Np and Pu isotopes. 242Pu as a pseudo isotope dilution tracer for Np, the negligible chemical fractionation between 237Np and 242Pu of 1.02 ± 0.06 (k = 2) was obtained by implementing sophisticated control of the redox system and chromatographic elution optimization. The analytical results for the International Atomic Energy Agency Certified Reference Materials (IAEA-443) agreed with the reference values, showing chemical yields of 65-88%, U decontamination factor above 106 level, and improved sample throughput (5 days for 12 samples). Meanwhile, the lower method detection limits (MDLs) of 237Np, 239Pu, and 240Pu were 1.3 × 10-3, 0.065, and 0.15 μBq L-1 for 15 L seawater, respectively. Results obtained by the developed method can be used to evaluate the impact on the marine ecological system of the planned marine discharge of Fukushima decontaminated wastewater. Working toward that purpose, we are the first to report the 237Np activity concentration in Pacific Ocean seawater sampled near the station site, and we obtained the value of 0.122-0.154 μBq L-1.

Simultaneous determination of femtogram levels of 237Np, 239Pu, and 240Pu in environmental solid samples using extraction chromatography and ICP-MS/MS

An analytical method based on triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) was developed for simultaneous determination of femtogram levels of ²³⁷Np, ²³⁹Pu, and ²⁴⁰Pu in environmental samples. By carefully controlling the valence states of Np and Pu in the entire separation procedure using a simple single extraction chromatographic column (TK200), the consistent behavior of Np and Pu was achieved, allowing for the reliable application of ²⁴²Pu as the chemical yield tracer for ²³⁷Np, ²³⁹Pu, and ²⁴⁰Pu. A high decontamination factor of 3.2 × 10⁷ for the most critical interfering element, uranium, was achieved in the chemical separation step. The interferences of ²³⁸U¹H⁺ and peak tailing of ²³⁸U⁺ during the measurement of plutonium isotopes were effectively eliminated by utilizing 7.5 mL/min He-1.1 mL/min CO₂ as reaction gases in the octupole collision/reaction cell and employing sequential quadrupole mode for mass separation in ICP-MS/MS. Specifically, the interference of ²³⁸U¹H⁺ was reduced to 10^-6 and the peak tailing of ²³⁸U⁺ to 10^-10, surpassing the performance of measurement method without reaction gases by 3 orders of magnitude. The developed method enables the accurate determination of femtogram levels of ²³⁷Np, ²³⁹Pu, and ²⁴⁰Pu in the samples with U/Np and U/Pu atom ratios of up to 10¹⁷ and 10¹², respectively. The developed method was validated by analyzing standard reference materials and spiked soil samples.

A novel strategy for Pu determination in water samples by automated separation in combination with direct ICP-MS/MS measurement

Methods for Pu determination in water samples has been longtime studied but they generally involved tedious manual operations. In this context, we proposed a novel strategy for accurate determination of ultra-trace Pu in water samples by the combination of fully automated separation with direct ICP-MS/MS measurement. A recently commercialized extraction resin TK200 was used for single-column separation due to its distinctive nature. Acidified waters up to 1 L were directly loaded to the resin at high flow rate (15 mL min^-1) with omitting the frequently used co-precipitation process. Small volumes of dilute HNO₃ were used for column washing, and Pu was efficiently eluted within only 2 mL 0.5 mol L^-1 HCl-0.1 mol L^-1 HF with a stable recovery (65%). This separation procedure was fully automated under the control of user program, meanwhile the final eluent was compatible for direct ICP-MS/MS measurement without extra sample treatment. In that way, both the labor intensity and reagent consumption were minimized compared with existing methods. With the high decontamination (10⁴ to 10⁵) of U in the chemical separation and the further elimination of uranium hydrides under oxygen reaction model during ICP-MS/MS measurement, the overall interference yields of UH⁺/U⁺ and UH₂⁺/U⁺ were down to 10^-15. The limits of detection (LODs) of this method reached 0.32 μBq L^-1 for ²³⁹Pu and 2.00 μBq L^-1 for ²⁴⁰Pu, which were much lower than those stipulated in the general guidelines for drinking water standards, suggesting this method was promising in routine or emergency radiation monitoring. Furthermore, the established method was successfully applied in a pilot study to determine global fallout derived Pu in surface glacier samples with extremely low concentrations of ^239+240Pu, which suggested the method would also be feasible in glacial chronology studies in the future.

Determination of uranium isotopes in marine sediments and seawaters by SF ICP-MS after rapid chemical separation using TK200 resin

This work provided a novel analytical procedure for rapid and precise uranium isotopic determination in marine sediment and seawater, using a new type of extraction resin, TK200 resin, in combination with microwave digestion (for marine sediments), Fe(OH)₃ co-precipitation (for seawater), and single collector sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) measurement. The removal ability of TK200 extraction chromatography for the interfering elements (IEs) Hg, Pb, Th, Pt, Tl, and the matrix rare earth elements (REEs) was carefully investigated. High decontamination factors (DFs) were obtained for IEs and REEs. Accurate quantification of uranium isotope ratios was accomplished based on a "double-cycle" ICP-MS measurement method. The analytical method was optimized and validated with isotopic standards (IRMM-187), matrix-containing certified reference marine sediments (IAEA-384, IAEA-385, and IAEA-412), and seawater reference material (IAEA-443). A stable chemical recovery of ~ 90% was obtained for both types of marine environmental samples, and the method showed great efficiency with a total analytical time of less than 6 h. The proposed procedure was validated following ISO/IEC 17025 guidelines. The important factors affecting the isotope ratio results (instrument background, procedural blank, memory effects, peak tailing, mass discrimination, dead time, and hydride interferences) were considered in the estimation of combined uncertainties. This work provides an alternative way for the determination of trace uranium isotope ratios and can be applied in the emergency monitoring of nuclear accidents and marine environmental analysis.

A review of anthropogenic radionuclide 236U: Environmental application and analytical advances

²³⁶U is an anthropogenic radionuclide that is produced from nuclear reactions of ²³⁵U(n, γ) and ²³⁸U(n, 3n). It has gained extensive attention in the field of environment, geology, nuclear emergency, and nuclear forensics. Due to the unique physical and chemical character and the distinct fingerprint character from different sources, ²³⁶U has been successfully applied in the environmental tracer, nuclear material source appointment, and environmental assessment. Until now, few reviews were published about the database, application, and the latest analytical technology development of ²³⁶U. In this review, the ²³⁶U concentration and ²³⁶U/²³⁸U isotope ratio were summarized, and the data were classified into four categories, including soil and seawater samples affected by global fallout and nuclear incidents. Furthermore, the development of environmental application and pretreatment methods were also summarized. The advanced pretreatment technology using alkali fusion and flow injection was especially discussed to introduce the development of a rapid analytical method. Finally, the research challenge and direction of ²³⁶U were proposed for further research, such as the tracer application combining ²³⁶U with other radionuclides in the terrestrial environment and the precise analysis of minor isotopes in ultra-trace uranium samples. We hope this review will help scholars to have a deep research on the analysis and application of ²³⁶U.

An improved rapid method for the determination of actinides in water

A new rapid method has been developed for the determination of Th, Pu, Np, U, Am and Cm isotopes in water samples of about 1 L. Actinides are pre-concentrated by co-precipitation with Ca phosphate, sequentially separated on stacked TEVA and TK221 cartridges and measured by alpha spectrometry. The TK221 extraction chromatographic resin contains i.e. CMPO and DGA extractants. It has been characterized by measuring the weight distribution ratios (Dw) of actinides which are higher than 1000 for all actinides in 3 M HNO3. The method has been optimized, applied for the analysis of tap and seawater samples and validated by participating in an IAEA proficiency test. Chemical recoveries for all actinides are better than 50%. The method can be performed within one day.

Dynamic Flow Approaches for Automated Radiochemical Analysis in Environmental, Nuclear and Medical Applications

Automated sample processing techniques are desirable in radiochemical analysis for environmental radioactivity monitoring, nuclear emergency preparedness, nuclear waste characterization and management during operation and decommissioning of nuclear facilities, as well as medical isotope production, to achieve fast and cost-effective analysis. Dynamic flow based approaches including flow injection (FI), sequential injection (SI), multi-commuted flow injection (MCFI), multi-syringe flow injection (MSFI), multi-pumping flow system (MPFS), lab-on-valve (LOV) and lab-in-syringe (LIS) techniques have been developed and applied to meet the analytical criteria under different situations. Herein an overall review and discussion on these techniques and methodologies developed for radiochemical separation and measurement of various radionuclides is presented. Different designs of flow systems with combinations of radiochemical separation techniques, such as liquid-liquid extraction (LLE), liquid-liquid microextraction (LLME), solid phase extraction chromatography (SPEC), ion exchange chromatography (IEC), electrochemically modulated separations (EMS), capillary electrophoresis (CE), molecularly imprinted polymer (MIP) separation and online sensing and detection systems, are summarized and reviewed systematically.

Establishing rapid analysis of Pu isotopes in seawater to study the impact of Fukushima nuclear accident in the Northwest Pacific

In order to assess the impact of the Fukushima derived Pu isotopes on seawater, a new analytical method to rapidly determine Pu isotopes in seawater by SF-ICP-MS including Fe(OH)₂ primary co-precipitation, CaF₂/LaF₃ secondary co-precipitation and TEVA+UTEVA+DGA extraction chromatographic separation was established. High concentration efficiency (~100%) and high U decontamination factor (~10⁷) were achieved. The plutonium chemical recoveries were 74–88% with the mean of 83 ± 5%. The precisions for both ²⁴⁰Pu/²³⁹Pu atom ratios and ^239+240Pu activity concentrations were less than 5% when 15 L of seawater samples with the typical ^239+240Pu activity of the Northwest Pacific were measured. It just needs 12 hours to determine plutonium using this new method. The limit of detection (LOD) for ²³⁹Pu and ²⁴⁰Pu were both 0.08 fg/mL, corresponding to 0.01 mBq/m³ for ²³⁹Pu and 0.05 mBq/m³ for ²⁴⁰Pu when a 15 L volume of seawater was measured. This method was applied to determine the seawater samples collected 446–1316 km off the FDNPP accident site in the Northwest Pacific in July of 2013. The obtained ^239+240Pu activity concentrations of 1.21–2.19 mBq/m³ and the ²⁴⁰Pu/²³⁹Pu atom ratios of 0.198–0.322 suggested that there was no significant Pu contamination from the accident to the Northwest Pacific.

Method for (236)U Determination in Seawater Using Flow Injection Extraction Chromatography and Accelerator Mass Spectrometry

An automated analytical method implemented in a flow injection (FI) system was developed for rapid determination of (236)U in 10 L seawater samples. (238)U was used as a chemical yield tracer for the whole procedure, in which extraction chromatography (UTEVA) was exploited to purify uranium, after an effective iron hydroxide coprecipitation. Accelerator mass spectrometry (AMS) was applied for quantifying the (236)U/(238)U ratio, and inductively coupled plasma mass spectrometry (ICPMS) was used to determine the absolute concentration of (238)U; thus, the concentration of (236)U can be calculated. The key experimental parameters affecting the analytical effectiveness were investigated and optimized in order to achieve high chemical yields and simple and rapid analysis as well as low procedure background. Besides, the operational conditions for the target preparation prior to the AMS measurement were optimized, on the basis of studying the coprecipitation behavior of uranium with iron hydroxide. The analytical results indicate that the developed method is simple and robust, providing satisfactory chemical yields (80-100%) and high analysis speed (4 h/sample), which could be an appealing alternative to conventional manual methods for (236)U determination in its tracer application.