Absorptiometric determination of microgram amounts of uranium with Rhodamine B

Uranium (VI) can be extracted as a complex with rhodamine B into a benzeneetherhexone solvent from a benzoate buffered solution. Optimum conditions for the colour development are defined, leading to a molar absorptivity of 102700 mmol^-1 cm² at 555 nm, the highest yet reported for a uranium complex. The determination of uranium in the range 0.02–3 μg/ml in nitrate samples is described. The relative standard deviation ranges from 20 to 0.6%. The interference of several ions is investigated.     

Extraction-photometric determination of uranium(IV) with chlorophosphonazo-III

A sensitive spectrophotometric method has been developed for the determination of uranium. The uranium(IV)-chlorophosphonazo-III complex is extracted into 3-methyl-1-butanol from 1.5–3.0 M hydrochloric acid solution. Maximal absorbance occurs at 673 nm and Beer's law is obeyed over the range of 0–15 μg per 10 ml of the organic phase. The molar absorptivity is 12.1·10⁴ 1 mole^?1 cm^?1. Uranium can be determined in the presence of fluoride. sulfate and phosphate. Nitrate ion and elements (chromium, copper, iron) which affect the reduction of uranium(VI) or stability of uranium(IV) interfere.     

Spectrophotometric determination of uranium in natural waters

A method for the spectrophotometric determination of uranium in samples of natural water is described. Ion exchange with Amberlite IR-120 (H⁺) to concentrate the metal was used. The absorption properties of the complex formed between uranium and the chromogenic reagent Arsenazo III, its stability over several hours, the effect of the pH on the ability of the resin to retain uranium, the reproducibility of the method and the effects of ionic interferences were considered. The sensitivity was 0.67 and 0.05 μg l^?1 of uranium for the direct and the addition methods, respectively. Uranium concentrations for the samples analysed were between 0.10 and 0.50 μg l^?1.     

Determination of natural uranium in biological samples using the solid state nuclear track detector method

For the solution of most of the problems which are connected to the biological and physiological role of natural uranium in plants and animal organisms about 10⁻¹⁴ g uranium should be determined. However most of the physico-chemical methods for the determination of natural uranium in biomaterials are time-consuming and possess considerable error. On the basis of addition and inner standard methods a version of Solid State Nuclear Track Detectors (SSNTD) method has been developed in order to determine the natural uranium in biospecimens. According to the experimental data simple relations have been obtained for the calculation of uranium concentration in biomaterial and minium uranium concentration in biosolution which can be measured by the detector used. Under irradiation of SSNTD at a thermal neutron flux of (3–5)·10¹⁵n·cm⁻² the detector sensitivity is 2.30·10⁻⁹ g U/ml for glass detectors; 9.60·10⁻¹⁰g U/ml for the detectors made from artificial mica.     

Determination of uranium isotopic composition in aqueous solutions by combined gamma-spectrometry and X-ray fluorescence

The possibility of use of combined gamma spectrometry and X-ray fluorescence for uranium isotopic analysis in dilute aqueous solutions has been studied. Uranium K X-rays were excited by gamma-rays of⁵⁷Co radionuclide source and were measured together with 185.7 keV gamma-rays of²³⁵U using a planar pure Ge detector. Uranium K_α1 fluorescent X-rays were used for the evaluation. The method was proved to be independent of total uranium concentration in the region of 8–20 mg U/ml. The procedure making use of measurement of 7 ml samples and allowing to achieve an accuracy better then 1% in the region of 0.4–4.5 at. % of²³⁵U is proposed.     

Precise isotope ratio measurements for uranium, thorium and plutonium by quadrupole-based inductively coupled plasma mass spectrometry

Precise long-term measurements of uranium and thorium isotope ratios was carried out in 1 μg/L solutions using a quadrupole inductively coupled plasma mass spectrometer (ICP-QMS). The isotopic ratios of uranium (²³⁵U/ ²³⁸U = 1, 0.02 and 0.00725) were determined using a cross-flow nebulizer (CFN, at solution uptake rate of 1 mL/min) and a low-flow microconcentric nebulizer (MCN, at solution uptake rate of 0.2 mL/min) over 20 h. For 1 μg/L uranium solution (²³⁵U/²³⁸U = 1) relative external standard deviations (RESDs) of 0.05% and 0.044% using CFN and MCN, respectively, can be achieved. Additional short term isotope ratio measurements using a direct injection high-efficiency nebulizer (DIHEN) of 1 μg/L uranium solution (²³⁵U/²³⁸U = 1) at a solution uptake rate of 0.1 mL/min yielded an RSD of 0.06–0.08%. The sensitivity of solution introduction by DIHEN for uranium, thorium and plutonium (145 MHz/ppm, 150 MHz/ppm and 177 MHz/ppm, respectively) increased significantly compared to CFN and MCN and the solution uptake rate can be reduced to 1 μL/ min in DIHEN-ICP-MS. Isotope ratio measurements at an ultralow concentration level (e.g. determination of ²⁴⁰Pu/ ²³⁹Pu isotope ratio in a 10 ng/L Pu waste solution) were carried out for the characterization of radioactive waste and environmental samples.     

Multielement analysis of uraniferous rocks by INAA: Special reference to interferences due to uranium and fission of uranium

The presence of uranium in a sample enhances the true values of La, Ce, Nd, Sm determined by INAA if appropriate corrections are not made for the interference. The enhancement of the true values comes about because the (n, γ) activation products of these elements, viz.¹⁴⁰La,¹⁴¹Ce,¹⁴⁷Nd,¹⁵³Sm, are also produced from the fission of²³⁵U (～0.72% natural isotopic abundance) even when La, Ce, Nd, Sm are totally absent in the given sample. In a 5 hour irradiation 1 μg of U is found to be equal to 0.28 μg of Ce and 0.23 μg of Nd while the equivalent La is found to be dependent upon the delay from end of irradiation to sample counting time. A numerical procedure is given to correct for these interferences. Spectral interferences from fission and (n, γ) β products of uranium in the determination of other trace elements by INAA is also investigated. Uranium is found to be determined best using the 278 keV gamma-ray of²³⁹Np.     

An automatic spectrophotometric method for the determination of uranium(VI) extracted into a liquid ion-exchanger medium

An earlier procedure based on 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol is adapted for use with a Technicon AutoAnalyzer; 60 samples per hour can be analyzed. The range is 0.2–3 g of uranium per litre of extract. The method is readily modified for the determination of uranium (?200 μg l^-1) in ground waters.     

Spectrophotometric determination of uranium in sea water with thiocyanate and rhodamine B

Summary Spectrophotometric Determination of Uranium in Sea-Water with Thiocyanate and Rhodamine B In the presence of a large excess of thiocyanate uranium(VI) forms a violet colour with Rhodamine B. The complex can be stabilized by addition of poly (vinyl alcohol). The calibration graph for measurement at 600 nm is linear in the range 0.5–10g of uranium per 25ml, the molar absorptivity being 3.56×10⁵1-mole^–1·cm^–1. The effect of foreign ions has been studied and the method can be applied to the determination of uranium in sea-water, with reliable results. Uranium is preconcentrated from sea-water by a flotation procedure with toluene in presence of benzoate and Safranine T, with nitrilotriacetic acid as masking agent. The method is highly selective for uranium, with a recovery of 97.9–99.2%.     

Development of method for determination and preconcentration of uranium in water samples using XAD-4 resin loaded with Br-PADAP

In the present work, a minicolumn of XAD-4 loaded with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) is proposed as a preconcentration system for uranium determination in well, tap and mineral water samples by spectrophotometer using arsenazo III as the chromogenic reagent. Initially, a two-level (2³) full factorial design was used for the preliminary evaluation of three factors, involving the following variables: sampling flow rate, elution flow rate, and pH. This design has revealed that, for the studied levels, buffer concentration and pH were significant factors. When the experimental conditions established in the optimization step were pH = 8.6, and an elution flow rate of 8.6 mL min^?1 using 0.5% m/v ascorbic acid, this system has allowed for the determination of uranium with a detection limit (LOD) (3σ/S) of 0.05 μg L^?1 and a quantification limit (LOQ) (10σ/S) of 0.16 μg L^?1. The precision expressed as the relative standard deviation (R.S.D.) of 0.8% and 1.9% at 10.0 and 1.0 μg L^?1, respectively- and a preconcentration factor of 184.5 for a sample volume of 50.0 mL. Accuracy was confirmed by uranium determination in the standard reference material, NIST SRM 1566b trace element units in Oyster Tissue samples, and spike tests with recuperations ranging from 93.2 to 105%; the procedure were applied for uranium determination in tap water, well water, and drinking water samples collected from Caetité and Cruz das Almas Cities, Bahia, Brazil. Five water samples were analyzed the uranium concentrations varied from 0.50 to 2.07 μg L^?1     

Determination of uranium(VI) in seawater by means of automated flow constant-current cathodic stripping at carbon fibre electrodes

Uranium(VI) is determined in an automated flow system by means of constant-current reductive stripping with a mercury film-coated carbon fibre electrode and catechol as adsorptive reagent at pH 8.6 Interference from iron(III) is eliminated by addition of sulphite. Increased linear range between stripping signal and sample uranium(VI) concentration can be obtained by adding, in the computer, several stripping curves, each obtained after a short period of adsorptive accumulation. It is shown that the hanging mercury drop electrode can be used for the determination of uranium(VI) by means of computerized constant current stripping without the need for inert gas bubbling. The results obtained for uranium(VI) in two reference seawater samples, NASS-1 and CASS-1, were 2.90 and 2.68 μg l^?1 with standard deviations (n = 8) of 0.57 and 0.75 μg l^?1, respectively.     

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%.     

Selective spectrophotometric determination of uranium

Uranium(VI) (10–100 μg) is extracted with 2% dibenzoylmethane in benzene at pH 6–7 while other cations are masked with CDTA (maximum of 8 μg/100 ml). Shaking with 6 M hydrochloric acid reintroduces uranium(VI) into the aqueous phase, where after evaporation and complexation with Arsenazo III in 0.02 M hydrochloric acid the final measurement of absorbance at 650 nm is performed. Iron(III), copper(II), aluminum, and zinc do not interfere even if present in amounts of 15–19 mmol.     

Spectrophotometric determination of trace uranium in geological samples by flow injection analysis with on-line levextrel resin separation and preconcentration

A flow-injection system with on-line separation and preconcentration is described for the spectrophotometric determination of trace uranium in geological samples. Uranium is selctively adsorbed from 0.7 mol l^?1 nitric acid on a microcolumn (40 mm long, 4.4 mm i.d.) containing levextrel CL-5209 resin (120–200 mesh) and separated from the sample matrix and most of the co-existing ions; 10-fold concentration is obtained. Eluted uranium is determined spectrophotometrically with arsenazo-III. The detection limit is μg l^?1 uranium and calibration is linear up to 0.3 mg l^?1 uranium With dual columns operated alternately for adsorption and elution, 30 samples can be analyzed per hour. Masking agents are added to eliminate interferences from thorium and iron. The method is sensitive and highly selective, easy to operate and suitable for routine analysis of geological samples for uranium.     

Determination of uranium using a flow system with reagent injection. Application to the determination of uranium in ore leachates

The determination of uranium by a flow system with reagent injection is based on the reaction of U(IV) with Arsenazo III in 3.6 M HCl; U(IV) is generated by reduction of uranyl ion in a lead reductor minicolumn installed in the sample channel of the manifold. The interference effect caused by several ions is studied. The calibration graph is linear up to 1.0 × 10^?5 M (2.4 mg l^?1) and the detection limit is 2.8 × 10^?8 M (6.6 μg l^?1). The modification of the manifold by including a second valve to by-pass the reducing column allows the measurement of the difference in peak heights, which makes the method specific for uranium.     

Determining of trace metals in nuclear-grade uranium dioxide by x-ray fluorescence spectrometry

A method is described for the simultaneous determination of low concentration of Ca, Cr, Cu, Fe, Mn and Ni in nuclear-grade uranium dioxide by x-ray fluroescence spectrometry, without the use of chemical treatment. The lower limits of detection range from 2 μg g^?1 for nickel and manganese to 5 μg g^?1 for copper. Samples are prepared in the form of double-layer pellets with boric acid as a binding agent. Standards are prepared in a U₃O₈ matrix, which is more chemically stable than UO₂ and has similar matrix behaviour. The correlation coefficients for calibration curves are better than 0.999. Errors range from 2.4% for chromium to 6.8% for nickel.     

Amberlite XAD-4 functionalized with succinic acid for the solid phase extractive preconcentration and separation of uranium(VI)

Amberlite XAD-4 resin has been functionalized with succinic acid by coupling it with dibromosuccinic acid after acetylation. The resulting resin has been characterized by FT-IR, elemental analysis and TGA and has been used for preconcentrative separation of uranium(VI) from host of other inorganic species prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption of uranium(VI) in both batch and column modes is 4.5-8.0 and desorption can be achieved by using 5.0 ml of 1.0 mol l⁻¹ HCl. The sorption capacity of functionalized resin is 12.3 mg g⁻¹. Calibration graphs were rectilinear over the uranium(VI) concentrations in the range 5-200 μg l⁻¹. Five replicate determinations of 50 μg of uranium(VI) present in 1000 ml of solution gave a mean absorbance of 0.10 with a relative standard deviation of 2.56%. The detection limit corresponding to three times the standard deviation of the blank was found to be 2 μg l⁻¹. Various cationic and anionic species at 200-fold amounts do not interfere during the preconcentration of 5.0 μg of uranium(VI) present in 1000 ml (batch) or 100 ml (column) of sample solution. Further, adsorption kinetic and isotherm studies were also carried out by a batch method to understand the nature of sorption of uranium(VI) with the succinic acid functionalized resin. The accuracy of the developed solid phase extractive preconcentration method in conjunction with Arsenazo III procedure was tested by analyzing marine sediment (MESS-3) and soil (IAEA soil-7) reference material. Further, the above procedure has been successfully employed for the analysis of soil and sediment samples.     

Preparation of soluble ternary heteroazo dye complexes for the spectrophotometric determination of trace uranium(VI)

The complexing ability of typical pyridylazo, quinolylazo and thiazolylazo dyes with uranium(VI) in aqueous ethanol media are investigated in the presence and absence of aromatic carboxylic acid. Uranium(VI) forms solubilized ternary complexes with PAN, PAR, TAM, 5-Br-PADAP, 3,5-diBr-PADAP and QADAP in 48% ethanol solution containing sufficient amounts of sulfosalicylic acid and triethanolamine buffer (pH 7.8). Aromatic carboxylic acids contribute to expel the coordinated water molecules from the uranium (VI) moiety and their chelating effects have been explained by ternary complex formation. An increase in molar absorptivity and no shift in the wavelength of maximum absorbance are observed for all uranium(VI) complexes investigated. The 11 stoichiometry of uranuim(VI) and heteroazo dye in the binary complex does not change through ternary complex formation. The molar absorptivity of the uranium(VI)-3,5-diBr-PADAP-sulfosalicylic acid ternary complex at 595 nm is 8.4×10⁴l mol^–1 cm^–1 and Beer's law is valid up to 2.5gmg ml^–1 of uranium(VI). The interferences due to coexisting metal ions can be effectively masked by addition of CyDTA or Ca-CyDTA.     

Optimization of the operating conditions using factorial designs for determination of uranium by inductively coupled plasma optical emission spectrometry

A critical evaluation of the determination of uranium by inductively coupled plasma optical emission spectrometry was performed using factorial designs (2³) involving the factors: acid concentration, radio frequency power and nebulizer gas flow rate. All of the experiments in this study were made for five emission lines, in the presence of nitric and hydrochloric acid. The results demonstrated that, between nitric and hydrochloric acid, the determinations in the presence of nitric acid were most sensitive. The factorial design showed that the nebulizer gas flow rate was the most significant among the factors studied for the five emission lines. Calcium in concentrations of 10 mg L⁻¹ was observed to cause suppression of the emission intensity for some lines. Iron (at least up to 10 mg L⁻¹) did not interfere in the emission intensity of uranium across the five lines studied. Another experiment evaluated simultaneously the effect of 13 other elements, and the results demonstrated that these elements did not affect the emission intensity of uranium for the lines chosen. The optimized method, using the line at 385.957 nm, allows the determination of uranium with limit of quantification of 31 μg L⁻¹ and precision expressed as RSD lower than 2.2% for uranium concentrations of either 500 or 1000 μg L⁻¹. The accuracy was confirmed by analysis of two laboratory reference materials. The developed method was applied to the determination of uranium in an industrial effluent collected from uranium-producing mine in Caetite City, Brazil. The sample was analyzed by inductively coupled plasma mass spectrometry ICP-MS, and the observed recovery was satisfactory.     

Determination of uranium in uranium hexafluoride material

A rapid and precise method has been developed for the determination of uranium in uranium hexafluoride material that contains essentially no non-volatile impurities. Approximately 7 g of uranium hexafluoride is transferred into a tared fluorothene tube, weighed, frozen, and hydrolyzed in 150 ml of ice-cold water in a platinum dish. The solution is evaporated to dryness, and the residue is ignited to urano-uranic oxide and weighed. The precision of a single analysis at the 95% confidence interval is ± 0.06% of the value, with no significant bias