Spectrophotometric determination of uranium(vi) by the azide reaction

Azide has been investigated as a spectrophotometric reagent for uranium(VI). The system is more sensitive than the thiocyanate reaction. It obeys Beer's law in the range 2–180 p.p.m. of uranium. The colour is sensitive to hydrogen ion concentration ; maximum absorbance and stability are attained at pH 5–5.5. Iron(III) interferes seriously, but can be masked by EDTA. Fe⁺², Cr⁺³, Ni⁺², Th⁺⁴, Cr₂O₇^-2, WO₄^-2, VO₃^- and F^- interfere. The deep yellow colour cannot be extracted with organic solvents. A mono-azido-uranium(Vl) ion is present in dilute solutions; its dissociation constant is 2.3 ±20.27·10^-3.     

Preconcentration of U(VI) from aqueous solutions after sorption using Sorel’s cement in dynamic mode

Summary Mg(OH)₂ was identified as a component of Sorel’s cement being a very strong sorbent for uranium. Sorel’s cement is a mixture of MgO, MgCl₂ and water. The optimal conditions for the adsorption of U(VI) was studied by the batch method. A contact time of 2 hours was found to be optimum. Maximum U(VI) uptake was observed in a pH range of 5.5-6.5 with a sorption constant of K_ads = 0.9 h^-1 at initial concentration of 20 ppm. Polypropylene columns filled with 2 g of Sorel’s cement at a mesh size of 35 were used for the preconcentration of uranium by passing 8 l of water containing 10 ppb U(VI). A flow rate of 0.25 ml/min and a bed height of 5 cm were found to be the optimum for the U(VI) separation. A 5 wt% triphenylphosphine oxide solution in toluene was used as an organic solvent for the separation of uranium from interfering elements such as iron(III) and thorium(IV), prior to spectrophotometric analysis. The determination of U(VI) was accomplished by adding Arsenazo III as a coloring reagent to the solution and using a UV-160A spectrophotometer.     

A fast and sensitive method for the determination of uranium in the Thorex Process streams

This paper presents a simple, rapid and sensitive radiometric method for the determination of uranium in Thorex Process stream containing large amount of thorium. This method involves the extraction of uranium into 0.05M tri-n-octyl phosphine oxide (TOPO) in xylene at 2M HNO₃. The extraction of thorium is prevented by masking them with suitable quantity of fluoride ions. The optimum experimental parameters for extraction of ²³³U were evaluated and using the most suitable experimental conditions the extracted uranium is radiometrically determined by α-counting in proportional counter with a prior knowledge of specific activity of uranium. Simultaneously in the same sample uranium was determined by spectrophotometric method using 2-(5bromo-2 pyridylazo)-5-diethylaminophenol (Bromo-PADAP) as chromogenic reagents. Simulated as well as actual samples of dissolver, conditioner and raffinate tank of Thorex stream have been analyzed by both these methods. The method was tested for as low as 0.15 μg of uranium and the results of these analyses were found to be satisfactory within the experimental limits.     

Determination of Ultra Trace Amounts of Uranium (VI) by Adsorptive Stripping Voltammetry Using L-3-(3, 4-dihydroxy phenyl) Alanine as a Selective Complexing Agent

Abstract

The spectrophotometric behavior of uranium (VI) with L-3-(3, 4-dihydroxy phenyl) alanine (LDOPA) reagent revealed that the uranium can form a ML₂ complex with LDOPA in solution. Thus a highly sensitive adsorptive stripping voltammetric protocol for measuring of trace uranium, in which the preconcentration was achieved by adsorption of the uranium-LDOPA complex at hanging mercury drop electrode (HMDE), is described. Optimal conditions were found to be a 0.02 M ammonium buffer (pH 9.5) containing 2.0 × 10^?5 M (LDOPA), an accumulation potential of ? 0.1 V (versus Ag/AgCl) and an accumulation time of 120 sec.

The peak current and concentration of uranium accorded with linear relationship in the range of 0.5–300 ng ml^?1. The relative standard deviation (at 10 ng ml^?1) is 3.6% and the detection limit is 0.27 ng ml^?1. The interference of some common ions was studied. Applicability to different real samples is illustrated. The attractive behavior of this reagent holds great promise for routine environmental and industrial monitoring of uranium.     

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     

The application of strongly reducing agents in flow injection analysis: Part 4. Uranium(III)

The application of uranium(III) in acidic medium as a powerful reducing reagent in flow injection analysis in detail. Results of the determination of a number of organic and inorganic substances are presented. With spectrophotometric detection based on the absorption by uranium(III) at 350 nm, limits of determination were of the order of 10^?5 mol 1^?1. For nitrate and nitrite, similar limits of determination were achieve with amperometric detection. This limit of determination is lower than in the case of chromium(II) and vanadium(II).     

Spectrophotometric Determination of Uranium(VI) with Chlorophosphonazo-mN by Flow Injection Analysis

Abstract

A sensitive and selective spectrophotometric flow injection analysis (FIA) method with chlorophosphonazo-mN has been developed for the determination of uranium(VI) in standard ore samples. Most of interfering ions are effectively eliminated by the masking reagent of diethylenetriaminepentaacetic acid (DTPA). In the U(VI)-chlorophosphonazo-mN system, the maximum absorption wavelength is at 680 nm and Beer's law is obeyed in the range of 1 to 15 μg ml^?1. The correlation coefficient of the calibration curve is 0.9998, the sampling frenquency is 60 h^?1, and the detection limit for uranium(VI) is 0.5 μg ml^?1. The composition of the U(VI)-chlorophosphonazo-nN complex was established to be 1:2 by flow-through spectrophotometric and conventional molar ratios methods.     

Determination of tarce water in non-polar organic solvents with a flow-injection system and tin tetrachloride or antimony pentachloride

Low levels of water (limit of detection 2-5 mg kg^1?)can be determined in a non-polar organic solvents such as benzene, 1,2-dichloroethane (DCE) and n-hexane by utilizing the reaction of water with SnCl₄ or SbCl₅. The reaction results of hydrolysis in halide and is accompanied by a decrease in optical absorption. With SnSl₄, the reaction is monitored near 300 nm and with SbCl₅ it is monitored at lower wavelengths (350-420). Niether reactons proceeds well in media containing only DCE and n-hexane. For this reason, the arrangemens involves a halide reagent dissolved in benzene which is merged with a benzene/n-hexane/DCE carrier stream into which samlpe is injected. A configuration in which only 2μl of a concentrated halide reagent solution is injected into the flowing sample stream is also shown to be viable for the determination of water in benzene. A membrane-permeation-based calibration method for preparing trace water standards is described.     

Repetitive determination of calcium ion and regeneration of a chromogenic reagent using chlorophosphonazo III and an ion exchanger in a circulatory flow injection system.

The spectrophotometric determination of Ca2+ with chlorophosphonazo III (CPN) has been carried out by a circulatory flow injection (FI) method. A cation-exchange mini-column for the on-line regeneration of the main reagent was incorporated in this FT system, allowing a repetitive determination of Ca2+. A solution of 4.0 x 10(-5) M CPN in a 0.05 M acetate buffer (pH 5.0) in a single reservoir (50 ml) was continuously circulated at a constant flow rate of 1.5 ml min(-1). Into the stream, an aliquot (20 microl) of a sample containing Ca2+ was quickly injected by means of a 6-way valve. The complex formed was monitored spectrophotometrically at 670 nm in the flow system. Then, the stream passed through a cation-exchange column, which was introduced after the flow-through cell. A successful ligand-exchange reaction of Ca2+ between the CPN reagent and a cation exchanger, as well as a simultaneous regeneration of the free reagent took place. The stream then returned to the reservoir. The regeneration and recycling of the CPN reagent allowed as many as 300 repetitive determinations of 2.5 mg l(-1) Ca2+ solutions with the same 50 ml circulating solution.     

Flow-injection spectrophotometric determination of aluminium based on chrome azurol S and cetylpyridinium chloride

Acidic aluminium solutions (120 μl) are injected into a buffered (pH 5.7) carrier stream and merge with a chrome azurol S/cetylpyridinium chloride stream; a 2.25-m reaction coil is used with a total flow rate of 4 ml min ^?1. Ethanol (30% v/v) in the reagent stream enhances the absorbance of the ternary complex; the molar absorptivity is then 1.34×10 ⁵ l mol ^?1 cm ^?1 at 625 nm. Calibration is linear over the range 0–400 ng ml^?1 aluminium; the limit of determination is 5 ng ml ^?1. Iron is masked in the usual way; fluoride is tolerated at ˇ1 mg l ^?1. The injection rate is about 45 h^?1. The procedure appears to be applicable to tap water.     

Determination of hydrogen peroxide in a flow system with microperoxidase as catalyst for the luminol chemiluminescence reaction

Hydrogen peroxide is determined by a chemiluminescence method with a reagent containing 100 μM luminol and 3 μM microperoxidase at pH 10 (carbonate buffer). Microperoxidase is superior to hematin as a catalyst. The method uses an automated flow injection system with a throughput of 2 samples per minute. The log—log calibration plot is linear (slope 1.3) from the detection limit, 3 × 10^-9 M up to 10^-5 M H₂O₂. The background emission is low. Impurities in the carrier stream and from some plastics may cause elevated background unless precautions are taken.     

Determination of ultra traces amount of uranium in raffinates of Purex process by laser fluorimetry

A simple and rapid, laser fluorimetric method for the determination of uranium concentration in raffinate stream of Purex process during reprocessing of spent nuclear fuel has been developed. It works on the principle of detection of fluorescence of uranyl complex formed by using fluorescence enhancing reagent like sodium pyrophosphate. The uranium concentration was determined in the range of 0–40 ppb and detection limit of 0.2 ppb. The optimum time discrimination is obtained when the uranyl ion is complexed with sodium pyrophosphate. Need of preconcentration step or separation of uranium from interfering elements is not an essential step.     

The application of strongly reducing agents in flow injection analysis: Part 1. Chromium(II) and vanadium(II)

Many reagenst cannot easily be applied in quantitative analysis, because of their instability under atmospheric conditions. When such reagents are prepared in a flowing stream, their applicability is very promising; for example, in flow injection analysis, a reagent need be stable only for 20–30 s. The application of chromium(II) and vanadium(II) in flow injection analysis is described. Nitrate and nitrile can be determined in the concentration range 5 × 10^?5?5 × 10^?3. Calibration graphs show good linearity.     

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.     

Simultaneous spectrophotometric determination of uranium and thorium by flow injection analysis using selective masking.

A flow injection system for the simultaneous determination of uranium and thorium has been developed by using selective masking and a spectrophotometric detector with two flow cells aligned with the same optical path. The injected sample solution was first mixed with a reagent solution containing Chromazurol S (CAS) and cetyltrimethylammonium chloride (CTMAC), and the total absorbance of uranium- and thorium-CAS complexes was measured in the first flow cell at 620 nm. The sample stream was then mixed with an EDTA solution in order to convert the thorium-CAS complex to a thorium-EDTA complex, and the absorbance of the uranium-CAS complex was measured in the second flow cell. The detection limits were 10 microg dm(-3) for uranium and 7 microg dm(-3) for thorium. The calibration graphs were linear (r < 0.9998) at least over the ranges of 0.1 to 10 mg dm(-3) for uranium and 0.08 to 8 mg dm(-3) for thorium. The RSDs were less than 1.5% (n = 3) in the calibration range. Uranium and thorium of up to the 6-fold concentration to each other could be determined in admixtures with relative errors of less than 3.3%. The sample throughput was 24 per hour. The proposed system was successfully applied to the analysis of a uranium-thorium ore mock solution by coupling with anion-exchange in a magnesium nitrate medium to eliminate interference from coexisting elements.     

Spectrophotometric determination of di(2-ethylhexyl), di(4-octylphenyl) and mono(4-octylphenyl)phosphoric acids with rhodamine-b

A spectrophotometric method for the determination of di(2-ethylhexyl). di(4-octylphenyl) and mono(4-octylphenyl) phosphoric acids is described. The method was applied for their determination in aqueous raffinates from uranium extraction processes where they are employed as extractants. The reagent was a dichloroethane extract of rhodamine-B prepared from an aqueous phosphate buffer of pH 10. The organophosphoric acids were separated from the aqueous solution by extraction with dichloroethane and this organic extract was mixed with rhodamine-B reagent. The intense colour produced had maximal absorbance at $\text{sol560}\text{565 nm.}$ The molar absorptivity was about 10⁵ in all cases.     

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.     

A titrimetric method for the sequential determination of thorium and uranium

A method for the sequential determination of thorium and uranium has been developed. In the sample solution containing thorium and uranium, thorium is first determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA) and then in the same solution uranium is determined by redox titration employing potentiometry. As EDTA interferes in uranium determination giving positive bias, it is destroyed by fuming with HClO₄ prior to the determination of uranium. A precision and accuracy of better than ±0.15% is obtained for thorium at 10mg level and uranium ranging from 5 mg to 20 mg in the aliquot.     

Separation and preconcentration of U(VI) on XAD-4 modified with 8-hydroxy quinoline

Amberlite XAD-4 adsorber resin was modified with 8-hydroxy quinoline (Oxine) by equilibrating with methanol solution of the reagent and the modified resin was used as a support material for the solid phase extraction and preconcentration of UO₂²⁺ from aqueous solution at pH between 4 and 5.5. Ten micrograms of uranium from 300 ml of aqueous phase could be quantitatively extracted in to 1 g of the modified resin giving an enrichment of 200. Uranium collected in the column could be eluted out with methanol-HCl mixture and determined spectrophotometrically using arsenazo(III) as the chromogenic reagent. The preconcentration could be made selective to uranium by using EDTA as a masking agent for transition metal ions and Th(IV).     

Sensitive and ultra-fast determination of arsenic(III) by gas-diffusion flow injection analysis with chemiluminescence detection

A novel chemiluminescence gas-diffusion flow injection system for the determination of arsenic(III) in aqueous samples is described. The analytical procedure involves injection of arsenic(III) samples and standards into a 0.3 mol L⁻¹ hydrochloric acid carrier stream which is merged with a reagent stream containing 0.2% (w/v) sodium borohydride and 0.015 mol L⁻¹ sodium hydroxide. Arsine, generated in the combined carrier/reagent donor stream, diffuses across the hydrophobic Teflon membrane of the gas-diffusion cell into an argon acceptor stream and then reacts with ozone in the flow-through chemiluminescence measuring cell of the flow system. Under optimal conditions, the method is characterized by a wide linear calibration range from 0.6 μg L⁻¹ to 25 mg L⁻¹, a detection limit of 0.6 μg L⁻¹ and a sample throughput of 300 samples per hour at 25 mg L⁻¹ and 450 samples per hour at 25 μg L⁻¹.