Total Reflection X-ray Fluorescence Spectrometric Analysis of Ten Lanthanides at the Ultratrace Level Having a High Degree of Overlap in the Emission Lines.

The extensive use of lanthanide elements in the medical, electrical, agricultural, and nuclear fields has increased their contamination in the environment. The detrimental effect of lanthanides on human health can be reduced or eliminated by their fast determination in the concerned specimen. For this purpose, an offline conjugation of the cloud point extraction (CPE) process with total reflection X-ray fluorescence (TXRF) spectrometry was done. This process was found to provide simple, quick, and precise simultaneous determination of ten lanthanides whose emission lines have a high degree of overlap at the ultratrace level. N,N,N',N'-tetra-octyl-diglycolamide in triton X-114 micelles was found to offer a selective CPE of all of the lanthanides in the presence of higher concentrations of naturally abundant cations and anions. A multivariative partial least-squares regression (PLSR) calibration approach was preferred due to the complex overlapped spectra of L lines of the lanthanides. Ten lanthanides, viz., La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, and Lu, were simultaneously determined by this method, having concentrations in the range from 10 to 5 × 103 µg L-1. The proposed method was validated by analyzing three certified reference materials (CRMs), viz., NASS-7 seawater, SRLS-6 river water, and NIST 1640a natural water, via standard addition with the relative standard deviations of ≤10%.

Selective Extraction of Thorium(IV) from Uranium and Rare Earth Elements Using Tetraphenylethane-1,2-diylbis(phosphoramidate).

Tetraphenylethane-1,2-diylbis(phosphoramidate) in conjugation with a room temperature ionic liquid in chloroform medium is reported for the first time in the liquid-liquid extraction of thorium (Th). The extracted Th(IV) is collected as a white solid in the organic medium, thereby facilitating its easy separation. A high distribution ratio (D) of (12.4 ± 0.1) × 103 in 2-8 mol L-1 acidity range and high decontamination factors (α) of Th(IV) from uranium, lanthanides, and a number of transition elements makes this extraction process versatile and selective. A number of experimental investigations in synergism with extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) studies are interpreted to confirm the structure of the chelated complex. A 1:2 metal/ligand complex in which the two oxygen and two nitrogen atoms of each bis(phosphoramidate) molecule satisfying the eight coordination sites of Th(IV) is found to be formed. The extracted white solid thorium complex is easily converted to ThO2 after washing and heating at 1300 °C under O2 atmosphere. This work is expected to find direct application in the thorium fuel cycle, especially in the mining process of thorium from its ores and in the separation of fissile 233U from fertile 232Th in irradiated fuel.

Cloud point extraction assisted spectrophotometric quantification of trace boron impurity in uranium-based nuclear fuels.

The separation of boron in nuclear fuels by cloud point extraction (CPE) has been a challenge due to high acidity of digested sample solutions. High acidity hampers the coacervation of micelles. As a result, the cloud point temperature increases and thus could cause the inevitable loss of boron as volatile species. Herein we have proposed a novel CPE-assisted colorimetric method for the quantification of traces of boron (B) in uranium-based fuels. A 1:1 mixture of 2-ethyl hexane-1,3-diol (EHD) and curcumin dispersed in Triton X-114 surfactant was used in the proposed CPE process. We had investigated several compounds to act as micelle surface modifiers. Among them, only bromine water (Br2) was found not only to lower the cloud point temperature (CPT, from 80 °C to 42 ± 2 °C) but also resulted in the quantitative recovery of boron (≥95%). The CPE of boron from uranium matrix in a 2.0 mol L-1 HCl medium was suitable for direct chemical quality assurance of routine uranium-based fuels. The molar extinction coefficient of the boron-EHD-curcumin complex was found to be 4.75 × 105 L mol-1 cm-1 (λmax at 458 nm) in N,N-dimethyl formamide medium. The linear dynamic range and detection limit of the proposed analytical procedure were calculated to be 10-150 ng mL-1 and 0.8 ng mL-1 respectively. The proposed analytical methodology was validated by analysis of three in-house working reference materials of uranium. Determination of traces of boron in two uranium dioxide and two metallic uranium samples were found to demonstrate the applicability of the method. The relative standard deviation of the proposed method was found to be of 3-5%.

Rapid and selective magnetic separation of uranium in seawater and groundwater using novel phosphoramidate functionalized citrate-Fe3O4@Ag nanoparticles.

One-pot magnetic separation of uranium (U) in seawater and groundwater samples has been made possible by synthesizing phosphoramidate functionalized Ag coated citrate-Fe3O4 nanoparticles (NPs). The magnetic saturation value of these functionalized NPs is 27.1 emu g-1. The synergistic extraction mechanism of U(VI) ion by the surface-modified phosphoramidate and citrate molecules make these NPs highly selective towards U(VI). The adsorption kinetics follows a pseudo-second-order model and the adsorption isotherm fits successfully to the Langmuir adsorption model. The functionalized NPs show quantitative extraction efficiency in the pH range of 6.5-8 with a maximum loading capacity (Qm) of 108.7 mg g-1. The equilibration time required by these functionalized NPs to attain the Qm value is 120 s. The recycling of these NPs can be done up to 5-6 times with 1.0 mol L-1 of Na2CO3 or NH4OH for quantitative extraction of U(VI). These functionalized NPs show high resilience towards large number of naturally abundant metal ions.

Colorimetric and visual determination of ultratrace uranium concentrations based on the aggregation of amidoxime functionalized gold nanoparticles.

The authors describe the synthesis and characterization of 3-mercaptopropionylamidoxime functionalized gold nanoparticles (AuNPs) for visual detection of uranium (U) by cloud point extraction. The method is capable of quantifying U at the concentration limits set by the World Health Organization in drinking water i.e., 30.0 ng mL-1. The method is based on the gradual color change from red to blue that occurs as a result of the interaction between uranyl ion and the modified AuNPs leading to particle aggregation. Such analyte-triggered aggregation results in AuNP's peak absorbance quenching as well as red shift in the wavelength range of 520 to 543 nm. The colorimetric response at 520 nm is linear in the 2-100 ng mL-1 U concentration range, and the limit of detection is 0.3 ng mL-1. No interferences by other ions are found, and the relative standard deviation is ≤4% (for n = 5). The method is validated by analyzing a certified reference material (NIST SRM 1640a; natural water), and also applied to the quantification of U in four (spiked) water samples. Graphical abstract Schematic presentation of cloud point extraction (CPE) assisted coloirmetric and visual detection of uranium (U). In CPE of gold nanoparticles (AuNPs) the color of surfactant rich phase (SRP) turns red in absence of U(VI) and blue in presence of U(VI).

Selective Micellar Extraction of Ultratrace Levels of Uranium in Aqueous Samples by Task Specific Ionic Liquid Followed by Its Detection Employing Total Reflection X-ray Fluorescence Spectrometry.

A task specific ionic liquid (TSIL) bearing phosphoramidate group, viz., N-propyl(diphenylphosphoramidate)trimethylammonium bis(trifluoromethanesulfonyl)imide, was synthesized and characterized by 1H NMR, 13C NMR, 31P NMR, and IR spectroscopies, elemental (C H N S) analysis, and electrospray ionization mass spectrometry (ESI-MS). Using this TSIL a cloud point extraction (CPE) or micelle mediated extraction procedure was developed for preconcentration of uranium (U) in environmental aqueous samples. Total reflection X-ray fluorescence spectrometry was utilized to determine the concentration of U in the preconcentrated samples. In order to understand the mechanism of the CPE procedure, complexation study of the TSIL with U was carried out by isothermal calorimetric titration, liquid-liquid extraction, 31P NMR and IR spectroscopies, and ESI-MS. The developed analytical technique resulted in quantitative extraction efficiency of 99.0 ± 0.5% and a preconcentration factor of 99 for U. The linear dynamic range and method detection limit of the procedure were found to be 0.1-1000 ng mL-1 and 0.02 ng mL-1, respectively. The CPE procedure was found to tolerate a higher concentration of commonly available interfering cations and anions, especially the lanthanides. The developed analytical method was validated by determining the concentration of U in a certified reference material, viz., NIST SRM 1640a natural water, which was found to be in good agreement at a 95% confidence limit with the certified value. The method was successfully applied to the U determination in three natural water samples with ≤4% relative standard deviation (1σ).