Calixarene-based Extraction Chromatographic Separation of 135Cs and 137Cs in Environmental and Waste Samples Prior to Sector Field ICP-MS Analysis

226Ra and 137Cs determination by inductively coupled plasma mass spectrometry: state of the art and perspectives including sample pretreatment and separation steps

Achieving precise and accurate quantification of radium (²²⁶Ra) and cesium (¹³⁷Cs) by inductively coupled plasma mass spectrometry (ICP-MS) is of particular interest in the field of radiological monitoring and more widely in environmental and biological sciences. However, the accuracy and sensitivity of the quantification depend on the analytical strategy implemented. Eliminating interferences during the sample handling step and/or during the analysis step is critical since presence of matrix elements can lead to spectral and non-spectral interferences in ICP-MS. Consequently, before the ICP-MS analysis, multiple sample preparation approaches have been applied to purify and/or pre-concentrate environmental and biological samples containing radium and cesium through years, such as (co)-precipitation, solid phase extraction (SPE) or dispersive SPE (dSPE). Separation steps using liquid chromatography and capillary electrophoresis can also be useful in complement with the abovementioned sample preparation techniques. The most attractive sample handling technique remains SPE but efficiency of the extraction procedures is currently limited by sorbent specificity. Indeed, with the recent advances in ICP-MS instrumentation, it becomes indispensable to eliminate residual interferences and improve sensitivity. It is in this direction that it will be possible to meet analytical challenges, e.g. analyzing radium and cesium at concentrations below the pg L^-1 range in complex matrices of small volumes, as they are found for instance in pore waters or in biological samples. Development of new innovative sorbents based for example on hybrid and nanostructured materials has been reported with the aim of enhancing sorbent specificity and/or capacity. In the present review, the performances of the different analytical approaches are discussed, followed by an overview of applications.

Regioisomers of singly bridged calix[6]crown-6 and their heavy alkali metal complexes: a molecular baseball glove for caesium(I)

We report the formation of heavy alkali metal complexes of bicyclic host molecules including the caesium(I) complex that catches the central metal ion with the deep pocket of the host similar to a baseball glove. For this, three regioisomers of singly bridged calix[6]crown-6 [1,2-bridged (H4 L 1,2), 1,3-bridged (H4 L 1,3) and 1,4-bridged (H4 L 1,4)] have been synthesized by alkyl-ation of calix[6]arene with penta-ethyl-ene glycol di-tosyl-ate in the presence of M 2CO3 (M = Na, K, Rb and Cs). The larger the cation size of the metal carbonate, the higher the yield of the H4 L 1,4 isomer, indicating the size-based template effect. A combination of H4 L 1,2 and RbOH allowed isolation of the mononuclear rubidium(I) complex (1) in which the metal center is six-coordinated in a loose fashion, the remaining two oxygen donors in the crown loop and two phenols in the calix rim are uncoordinated. Notably, the complexation of H4 L 1,2 with CsOH yielded the mononuclear caesium(I) complex (2), in which all possible ten binding sites on the deep and good-fit pocket participate in coordination via high cooperativity between the crown loop and calix rim, similar to a baseball glove. In dipolar organic solution, the caesium(I) complex 2 remains intact. H4 L 1,4 afforded a dicesium(I) complex (3) and adjacent complexes are linked by intermolecular cation-π interactions, giving rise to a pseudo one-dimensional coordination polymer. These results provide insight into the metal carbonate-dependent synthesis of calix[6]crowns and the influence of regioisomers on caesium(I) complexation.

Determination of low-level 135Cs and 135Cs/137Cs atomic ratios in large volume of seawater by chemical separation coupled with triple-quadrupole inductively coupled plasma mass spectrometry measurement for its oceanographic applications

Radioisotopes of cesium are powerful tracer for oceanographic studies. In this work, a novel method was developed for determination of ultra-low level ¹³⁵Cs and ¹³⁷Cs in seawater using triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Cesium was pre-concentrated from up to 45 L seawater samples using ammonium molybdophosphate (AMP) adsorption, following a selective leaching of cesium using Sr(OH)₂. The cesium was further purified from interfering elements using AMP-PAN and cation-exchange chromatography. Sr(OH)₂ leaching was found to be an effective approach for selective exchange of cesium from the AMP sorbent without dissolution, which avoids the problem of separation of huge amount of NH₄⁺ and MoO₄^2- in the following steps. The decontamination factors for barium and rubidium with the developed method were more than 4 × 10⁷ and 800, respectively. The separated ¹³⁵Cs and ¹³⁷Cs were measured using ICP-MS/MS by employing N₂O as reaction gas to further elimination of isobaric (i.e. ¹³⁵Ba and ¹³⁷Ba) and polyatomic ions interferences. A detection limit of 1.5 × 10^-16 g L^-1 for ¹³⁵Cs in seawater was achieved. The concentrations of ¹³⁵Cs in seawater from Baltic Sea, Danish straits and Roskilde Fjord were determined using the developed method to identify the sources of ¹³⁵Cs, the water masses exchange in this region was investigated using ¹³⁵Cs and ¹³⁷Cs.

Macrocyclic Pyridone Pentamers for Highly Selective High-Capacity Removal of Caesium Ions from Radioactive High-Salinity Waste

We report here that macrocyclic H-bonded pyridone pentamers, containing five properly and convergently spaced electron-rich O-atoms that decorate a rigid cavity of 2.85 Å across, exhibit an extraordinarily high yet pH-independent capacity and selectivity in Cs⁺ removal. In particular, with [host]=240 μM and [Cs⁺ ]=15 μM, a single extraction efficiently removes more than 91% of Cs⁺ ions from artificial sea water, containing various competitive metal ions at a total concentration of 0.68 M ([total Mⁿ⁺ ]/[Cs⁺ ]=4.5×10⁴ ]). To our best knowledge, these pyridone pentamers represent the best small organic molecule-based extractants that target Cs⁺ ions.

Determination of Ultralow Level 135Cs and 135Cs/137Cs Ratio in Environmental Samples by Chemical Separation and Triple Quadrupole ICP-MS

An analytical method was developed for the determination of ultralow level ¹³⁵Cs in environmental samples by chromatographic separation of cesium with AMP-PAN and AG50W-X8 columns and sensitive measurement of cesium isotopes with triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Cesium was simply released by acid leaching using aqua regia from environmental solid samples and preconcentrated on AMP-PAN column. The cesium adsorbed on the column was effectively eluted with NH₄Cl solution without dissolving the AMP. The excessive amount of NH₄Cl in the eluate was removed by sublimation in the presence of small amount of LiCl. The remaining barium and other interfering elements such as Mo, Sn, Sb, and Li were efficiently removed using cation exchange chromatography (AG50W-X8). The decontamination factors of this procedure are above 4 × 10⁷ for barium and 4 × 10⁵ for molybdenum; the chemical yields of cesium are more than 85% for samples of less than 10 g. This method enables to separate cesium from large size of samples for the determination of ultralow level ¹³⁵Cs, avoiding the problem of removal of a huge amount of Mo in the dissolved AMP. Intrinsic ¹³⁷Cs in the environmental samples measured by gamma spectrometry before and after separation was used as internal isotope dilution standard for quantitative determination of ¹³⁵Cs without complete release and recover of radiocesium. The interference of barium (¹³⁵Ba and ¹³⁷Ba) to the ICP-MS measurement of ¹³⁵Cs and ¹³⁷Cs was further suppressed to 8 × 10^-5 by using N₂O as the reaction gas in ICP-MS/MS at a flow rate of 0.7 mL/min, so a total suppression of 2 × 10^-12 for Ba was achieved, making the isobaric interference of Ba isotopes to the measurement of ¹³⁵Cs and ¹³⁷Cs in environmental samples negligible. A detection limit of 9.1 × 10^-17 g/g for ¹³⁵Cs and ¹³⁷Cs was achieved for 60 g samples. The developed method was validated by analysis of standard reference materials (IAEA-375, IAEA-330, and IAEA-385) and successfully applied for the determination of ¹³⁵Cs concentrations and ¹³⁵Cs/¹³⁷Cs ratios in soil samples collected from Denmark, Sweden, and Ukraine. The ¹³⁵Cs/¹³⁷Cs isotopic ratios in Danish soil (2.08-2.68) were significantly higher than that from Sweden and Ukraine (0.65-0.71), indicating different sources of radiocesium. This work demonstrated the application of ¹³⁵Cs/¹³⁷Cs as a unique fingerprint for discriminating the sources of radioactive contamination and estimating their contribution to the total inventory, which will be useful for nuclear forensics and environmental tracer studies.

Determination of Ultratrace Level 135Cs and 135Cs/137Cs Ratio in Small Volume Seawater by Chemical Separation and Thermal Ionization Mass Spectrometry

The atomic ratio of ¹³⁵Cs/¹³⁷Cs is a powerful fingerprint for distinguishing the source terms of radioactive contamination and tracing the circulation of water masses in the ocean. However, the determination of the ¹³⁵Cs/¹³⁷Cs ratio is very difficult due to the ultratrace level of ¹³⁵Cs (<0.02 mBq/m³) and ¹³⁷Cs (<2 Bq/m³) in the ordinary seawater samples. In this work, a sensitive method was developed for determination of ¹³⁵Cs concentration and ¹³⁵Cs/¹³⁷Cs ratio in seawater using chemical separation combined with thermal ionization mass spectrometry (TIMS) measurement. Cesium was first preconcentrated from seawater using ammonium molybdophosphate-polyacrylonitrile column chromatography and then purified using cation exchange chromatography to remove the interferences. With this method, decontamination factors of 6.0 × 10⁶ for barium and 1800 for rubidium and a chemical yield of more than 60% for cesium were achieved. By using glucose as an activator, the ionization efficiency of cesium was significantly improved to 50.6%, and a constant high current of Cs⁺ (20 V) can be maintained for more than 180 min, which ensures sensitive and reliable measurement of low level ¹³⁵Cs and ¹³⁷Cs. Detection limits of 4.0 × 10^-17 g/L for both ¹³⁵Cs and ¹³⁷Cs for 200 mL seawater were achieved, which enables the accurate determination of ¹³⁵Cs concentration and ¹³⁵Cs/¹³⁷Cs ratio in a small volume of seawater samples (<200 mL). The developed method has been validated by analysis of seawater reference material IAEA-443. Seawater samples collected from the Greenland Sea, Baltic Sea, and Danish Straits have been successfully analyzed for ¹³⁵Cs concentrations and ¹³⁵Cs/¹³⁷Cs ratios, and the results showed that ¹³⁵Cs concentrations in the seawater of the Baltic Sea is much higher than that in the Greenland Sea, which is attributed to the high deposition of Chernobyl accident derived radiocesium in the Baltic Sea region.

Direct Quantitation of 135Cs in Spent Cs Adsorbent Used for the Decontamination of Radiocesium-Containing Water by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

The long-term safety assessment of spent Cs adsorbents produced during the decontamination of radiocesium-containing water at the Fukushima Daiichi nuclear power plant requires one to estimate their ¹³⁵Cs content prior to final disposal. ¹³⁵Cs is usually quantified by inductively coupled plasma mass spectrometry (ICP-MS), which necessitates the elution of Cs from Cs adsorbents. However, this approach suffers from the high radiation dose from ¹³⁷Cs that is present in the contaminated water and Cs adsorption irreversibility. To address these challenges, we herein employed laser ablation ICP-MS for direct quantitation of ¹³⁵Cs in Cs adsorbents and used a model Cs adsorbent prepared by immersion of a commercially available Cs adsorbent into radiocesium-containing liquid waste to verify the developed technique. Crushing and subsequent coating with a nitrocellulose-based curing agent provided a thin flat surface and thus allowed for stable solid sampling during laser ablation. The use of the ¹³⁵Cs/¹³⁷Cs ratio and ¹³⁷Cs radioactivity obtained by gamma spectrometry achieved simple and precise quantitation of ¹³⁵Cs. The obtained ¹³⁵Cs/¹³⁷Cs ratio of 0.41 ± 0.02 well agreed with that obtained for the original liquid waste sample by solution nebulization measurements, and the proposed method was concluded to be suitable for large-scale ¹³⁵Cs quantitation, requiring only very small (<10 mg) samples with total ¹³⁷Cs radioactivity.

Novel and Innovative Interface as Potential Active Layer in Chem-FET Sensor Devices for the Specific Sensing of Cs. ACS APPLIED MATERIALS & INTERFACES 2019;11:47635-47641. [PMID: 31769645 DOI: 10.1021/acsami.9b18188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

An innovative novel interface has been designed and developed to be used as a potential active layer in chemically sensitive field-effect transistor (Chem-FET) sensor devices for the specific sensing of Cs⁺. In this study, the synthesis of a specific Cs⁺ probe based on calix[4]arene benzocrown ether, its photophysical properties, and its grafting onto a single lipid monolayer (SLM) recently used as an efficient ultrathin organic dielectric in Chem-FETs are reported simultaneously. On the basis of both optical and NMR titration experiments, the probe has shown high selectivity and specificity for Cs⁺ compared to interfering cations, even if an admixture is used. Additionally, Attenuated Total Reflectance Fourier Transform Infra Red (ATR-FTIR) spectroscopy was successfully used to characterize and prove the efficient grafting of the probe onto a SLM and the formation of the innovative novel sensing layer.

Recognition and Extraction of Cesium Hydroxide and Carbonate by Using a Neutral Multitopic Ion-Pair Receptor

Current approaches to lowering the pH of basic media rely on the addition of a proton source. An alternative approach is described herein that involves the liquid-liquid extraction-based removal of cesium salts, specifically CsOH and Cs₂ CO₃ , from highly basic media. A multitopic ion-pair receptor (2) is used that can recognize and extract the hydroxide and carbonate anions as their cesium salts, as confirmed by ¹ H NMR spectroscopic titrations, ICP-MS, single-crystal structural analyses, and theoretical calculations. A sharp increase in the pH and cesium concentrations in the receiving phase is observed when receptor 2 is employed as a carrier in U-tube experiments involving the transport of CsOH through an intervening chloroform layer. The pH of the source phase likewise decreases.

Efficient and Selective Enrichment of Ultratrace Cytokinins in Plant Samples by Magnetic Perhydroxy-Cucurbit[8]uril Microspheres

Cytokinins play a critical role in controlling plant growth and development, but it is difficult to be determined in plant samples due to the extremely low concentration level of picomole/gram. So it is important for efficient sample preparation with selective enrichment and rapid separation for accurate analysis of cytokinins. Herein, a supramolecular perhydroxy-cucurbit[8]uril (PCB[8]) was fabricated into the Fe3O4 magnetic particles via chemical bonding assembly and magnetic perhydroxy-cucurbit[8]uril (MPC) materials were obtained. The MPC had good enrichment capability to cytokinins and the enrichment factors were more than 208. The interaction of MPC and cytokinins was investigated by adsorption test and density functional theory (DFT) calculation, the results showed that the main drive forces were the host-guest interaction and hydrogen-bonding interaction between the perhydroxy-cucurbit[8]uril with analytes. Combined with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), the MPC was used as a sorbent of magnetic solid-phase extraction for the analysis of cytokinins in plant samples. A sensitive and selective UPLC-MS/MS method was developed with low detection limits of 0.14-0.32 ng/L for cytokinins analysis. Five cytokinins including zeatin riboside, meta-topolin, kinetin, kinetin riboside, and zip with 6.12-87.3 ng/kg were determined in the soybean sprout and Arabidopsis thaliana. The recoveries were in the range of 76.2-110% with relative standard deviations (n = 5) of 2.3-9.7%. On the basis of these results, magnetic perhydroxy-cucurbit[8]uril materials with selective enrichment capability have good potential on the analysis of ultratrace targets from complicated sample matrixes.