A simple and reliable method for rapid extraction and determination of uranium in natural waters using octadecyl-bonded silica membrane disks modified with tri-n-octylphosphine oxide (TOPO) and spectrophotometry with dibenzoylmethane is presented. Extraction efficiency and the influence of sample matrix, type, and optimum amount of extractant, flow rates, and type and minimum amount of organic eluent were evaluated. The maximal capacity of the membrane disks modified by 50 mg of TOPO was found to be 4033 μg of uranium. The limit of detection of the proposed method is 100 ng/1000 mL. The method was applied to the extraction and determination of uranium in natural waters.

Solid-Phase Extraction of Ultratrace Uranium(VI) in Natural Waters Using Octadecyl Silica Membrane Disks Modified by Tri-n-octylphosphine Oxide and Its Spectrophotometric Determination with Dibenzoylmethane

The equilibrium solubility of uranyl nitrate in supercritical fluid carbon dioxide (SF-CO 2 ) in the absence and presence of different modifiers was investigated. In the presence of methanol and HNO 3 , uranyl nitrate showed a considerable solubility in SF-CO 2 . SF-CO 2 modified with different co-extractants such as tributylphosphate (TBP), methylisobutyl ketone (MIBK), acetylacetone (AA) and methanol (MeOH) at 60°C and 250 atm was used for the extraction of uranyl nitrate from cellulose-based filter papers. The extraction efficiency of the system for uranyl ion was found to decrease in the order TBP>MIBK>AA>MeOH. The use of eight potential chelating agents bis (2-ethylhexyl)hydrogen phosphate (HDEPH), tri- n -octylphosphine oxide (TOPO), dicyclohexyl-18-crown-6 (DC18C6), dibenzoylmethane (DBM), 8-hydroxyquinoline (HOX), diphenylaminesulfonic acid (DPASA) 1,4- bis -[4-methyl-5-phenyl-2-oxazolyl]benzene (DMPOPOP) and TBP for uranyl ion extraction from filter paper samples by methanol modified SF-CO 2 was investigated. The organophosphorous reagents TOPO and HDEPH showed the highest extraction efficiency in the series. The synergistic extraction of uranyl nitrate with HDEPH and TOPO in the presence of DC18C6 was also studied.

Extraction of uranium from solid matrices using modified supercritical fluid CO2

A simple method for rapid and selective separation of uranyl ion from Th4+ and other accompanying elements by using octadecyl silica membrane disks modified with tri-n-octyl phosphine oxide (TOPO) in the presence of 0.5 M HNO3 is presented. The influences of type and concentration of acid, nature of ligands, flow rates, and nature of stripping agents have been investigated. Maximum capacity of the membrane disks modified by 50 mg TOPO was found to be 938 μg of uranium. The method was applied to the recovery of uranyl ion from two different soil samples.

A Rapid Method for the Extraction and Separation of Uranium from Thorium and Other Accompanying Elements Using Octadecyl Silica Membrane Disks Modified by Tri-n-octyl Phosphine Oxide

A simple and efficient method for the selective separation and preconcentration of uranium(VI) using homogeneous liquid-liquid extraction was developed. Tri-n-octylphosphine oxide (TOPO) and tri-n-butylphosphate (TBP) were investigated as complexing ligands, and perfluorooctanoate ion (PFOA-) was applied as a phase separator agent under strongly acidic conditions. Under the optimal conditions ([PFOA-] = 1.7 x 10(-3) M, [TOPO] = 5.4 x 10(-4) M, [HNO3] = 0.3 M, [acetone] = 3.2% v/v) 10 microg of uranium in 40 ml aqueous phase could be extracted quantitatively into 8 microl of the sedimented phase. The maximum concentration factor was 5000-fold. However, an effort for the quantitative extraction using TBP was inefficient and the percent recovery was at most 56.7. The influence of the type and concentration of acid solution, optimum amount of the ligand, type and volume of the organic solvent, concentration of PFOA, volume of the aqueous sample and effect of different diverse ions on the extraction and determination of uranium(VI) were investigated. The proposed method was applied to the extraction and determination of uranium(VI) in natural water samples.

Homogeneous liquid-liquid extraction of uranium(VI) using tri-n-octylphosphine oxide.

Extractive electrospray ionization (EESI) mass spectrometry (MS), a typical MS platform for detection of organic compounds, has been used for quantitative detection of uranium isotopic ratio (235U/238U) in uranyl nitrate solution samples, which were prepared from various samples including natural water samples, uranium ore samples and soil samples using nitric acid. This method requires minimal sample pretreatment and no high resolution instruments. The typical time for analysis of a single liquid sample was about 5 min since the prepared sample solutions were directly infused into the EESI source without separation or preconcentration. The relative errors for uranium isotope measurements were in the range of 0.21%–0.25% and the corresponding relative standard deviation (RSD) values were 1.54%–1.81% for the ore samples. The results obtained by EESI-MS for direct analysis of 5 soil samples were validated by using ICP-MS. These findings confirmed that EESI-MS can be employed for quantitative measurement inorganic compounds present in a complex matrix. The fast detection of uranium isotopes shows potential applications of EESI-MS in nuclear research laboratories and the nuclear energy industry.

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Determination of uranium isotopic ratio (235U/238U) using extractive electrospray ionization tandem mass spectrometry

A method is described for the determination of trace amounts of uranium (down to 10 µg l–1) in natural waters by differential-pulse polarography of a cyclohexane-trioctylphosphine oxide extract. Studies on the effect of possible interferences are included.

R. L. Deutscher

Papers

Determination of uranium in natural waters by differential-pulse polarography of a trioctyl-phosphine oxide extract