Spectrophotometric determination of uranium using ascorbic acid as a chromogenic reagent

A spectrophotometric method has been developed for the determination of uranium(VI) using ascorbic acid. Uranium in the hexavalent state forms a reddish-brown coloured complex with ascorbic acid. The colour intensity of the complex is maximum at pH 4.2-4.5 and is stable for 24 hr. The absorbances of uranium(VI)-ascorbic acid complex at 360 and 450 nm are used for its quantification. Uranium in the range 8-200 microg/ml has been determined with good precision. The method allows the determination of uranium in the presence of many metal ions present as impurities. The described method is simple, accurate and applicable to uranium concentration relevant to the PUREX process and thus can be used for analytical control purposes.     

Solvent extraction and spectrophotometric determination of uranium(VI) with pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone

Pyridine-2-carboxaldehyde 2-hydroxybenzoylhydrazone (PAHB) is proposed as an extractant for the separation and spectrophotometric determination of uranium(VI). The optimum extraction conditions have been evaluated by studying various parameters such as pH, diluents, equilibration time and reagent concentration. PAHB forms yellow colored complex with uranium(VI) in the pH range of 3.5-4.6 which can be extracted by isobutyl methyl ketone. The extracted complex exhibits an absorption maximum at 375 nm. Beer's law was obeyed in the concentration range 1.0-5.6 ppm of uranium(VI). The nature of the extracted species (1:2) was determined by log D-log c plot. The proposed method permits selective separation of uranium(VI) from its binary mixtures. The method is also applied for the estimation of uranium in multicomponent mixtures and monazite sand.     

Photometric determination of trace uranium(VI), phosphorus(V), arsenic(V), and vanadium(V) in saturated aqueous solutions of poorly soluble compounds

A procedure for extraction-photometric determination of uranium(VI) was developed and procedures for the determination of phosphorus(V), arsenic(V), and vanadium(V) were modernized. The solubility of some poorly soluble uranium compounds in aqueous solutions was determined. Deceased.     

Differential pulse polarographic determination of uranium(VI) in complex materials after adsorption of its trifluoroethylxanthate cetyltrimethylammonium ion-associated complex on naphthalene adsorbent.

Uranium(VI) is adsorbed as a uranium trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion-pair complex on microcrystalline naphthalene quantitatively in the pH range 4.2 - 7.0. Without cetyltrimethylammonium as the counter ion, the adsorption is hardly 70%. The metal has been desorbed with HCI and determined with a differential pulse polarograph. Uranium can alternatively be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1 - 5 ml/min and determined similarly. A well-defined peak has been obtained in this medium at -0.20 V versus a saturated calomel electrode. Cyclic voltammetry, differential pulse polarography and D.C. polarography studies indicate that uranium has been reduced irreversibly under these conditions. The detection limit is 0.30 microg/ml at the minimum instrumental settings (signal-to-noise ratio of 2) (with a preconcentration factor of 10, the detection limit would be 30 ng/ml for uranium when the volume in the cell is 15 ml). However if the volume in the cell is 5 ml, it would have been 10 ng/ml with a preconcentration factor of 30. Linearity is maintained in a concentration range of 0.5 - 19.0 microg/ml (2.1 - 79.83 x 10(-9) M) with a correlation factor of 0.9994 and a relative standard deviation of +/-1.1% (in this case 7.5 microg may be concentrated from 150 ml of the aqueous sample where its concentration is as low as 50 ng/ml). Various parameters, such as the effect of the pH, volume of the aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of uranium, have been studied in detail to optimize the conditions for its trace determination in various complex materials, like alloys, coal fly ash, biological, synthetic, and waste-water samples.     

Improved spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol in the presence of benzyldimethylstearyltrimethylammonium chloride

An improved spectrophotometric determination of uranium(VI) is proposed using 4-(2-pyridylazo)resorcinol(PAR) in the presence of benzyldimethylstearyltrimethylammonium chloride(BSTAC) as a cationic surfactant. The calibration graph is linear in the range of 0.3-60 microg/10 ml uranium(VI), measuring the absorbance at 550 nm. The reproducibility for 19.0 microg/10 ml uranium(VI) is 0.57%. The third-derivative method using the third-derivative distance (d(3)A/dlambda(3)) among lambda(1) 530 nm, lambda(3) 594 nm and lambda(2) 565 nm was also investigated.     

Spectrophotometric method for the determination of vanadium in uranium rich hydrogeochemical samples using pyridyl azo resorcinol (PAR)

A simple and precise method has been developed for the determination of traces of vanadium(V), using 4-(2 pyridyl azo) resorcinol, in natural water samples, containing very high concentrations of uranium. CDTA-pyrophosphate buffer has been used for masking interferants, including uranium which otherwise interferes above 125 ppb. The reaction of vanadium with PAR in the presence of buffer requires a waiting period of 45 min. The Sandell sensitivity of the method is 0.003 microg/ml, at 545 nm at an optimum pH of 6.5 +/- 0.2. The precision of the method is +/- 15% at the 100 ppb level of vanadium(V). The method has been successfully applied to a number of natural water samples during hydrogeochemical exploration.     

Spectrophotometric determination of vanadium in different oxidation states with pyrogallol

Determination of vanadium at low concentrations is easily performed with pyrogallol as a ligand which forms a bluish-violet complex with vanadium(III), (IV) or (V). The colour of the bluish-violet complex (lambda(max) = 580 nm) contrasts well with the colour of both pyrogallol and vanadium. The complexes are stable for several hours. Beer's law is obeyed over the range 0-14 mug/ml vanadium at pH 6. The apparent molar absorptivity at 580 nm is (7.75 +/- 0.25) x 10(3)1.mole(-1).cm(-1). The effects of diverse ions on the determination of vanadium have been fully studied. Only Mo(VI) and W(VI) interfere seriously. The method is selective, sensitive and can be applied to the determination of total vanadium in a variety of samples.     

Liquid-liquid extraction of niobium(V) in the presence of other metals with high molecular mass amines and ascorbic acid

A novel method is proposed for the solvent extraction of niobium(V). A 0.1M solution of Aliquat 336S in xylene quantitatively extracts microgram quantities of niobium(V) from 0.01M ascorbic acid at pH 3.5-6.5. Niobium from the organic phase is stripped with 0.5M nitric acid and determined spectrophotometrically in the aqueous phase as its complex with TAR. The method permits separation of niobium not only from tantalum(V) but also from vanadium(IV), titanium(IV), zirconium(IV), thorium(IV), chromium(III), molybdenum(VI), uranium(VI), iron(III), etc. Niobium from stainless steel was determined with a precision of 0.42%.     

Preconcentration and determination of uranyl ions on electrodes modified by tri-n-octylphosphine oxide

The application of electrodes modified by tri-n-octylphosphine oxide (TOPO) to the determination of uranium in aqueous solutions is investigated. Selective preconcentration of uranium(VI) by chemical reaction with the modifying molecule is followed by cyclic voltammetry. A hanging mercury drop electrode (HMDE) can be modified easily but the reproducibility of results is not good. When a TOPO-modified glassy carbon electrode is used, uranium(VI) can be preconcentrated from stirred solutions, and the cathodic voltammograms show an increase of current or a peak at about -0.75 V vs. SCE, depending on the uranium concentration of the solution. The effects of preconcentration time, pH and electrode potential during the preconcentration are discussed. The detection limit is in the 10^-9 M range for 45 min of preconcentration. The procedure is fairly selective for uranyl ions, but oxidizing agents interfere. Some tests on sea water are reported.     

Flow-injection spectrophotometric determination of trace vanadium based on catalysis of the gallic acid bromate reaction

High sensitivity is obtained by using high concentrations of gallic acid and bromate, although the uncatalyzed reaction is significant. Various reactant concentrations, reaction temperature, pH and residence times can be used to alter the linear calibration ranges and sensitivity for vanadium. With reagent streams of 1.76 M bromate and 0.06 M gallic acid at pH 3.8 (each at 1 ml min^?1), 0.2–20 ng of vanadium (20-μl injections) can be determined at 30°C. Oxidized gallic acid is detected at 380 nm. When the bromate concentration is decreased to 0.5 M and the temperature is 65°C, 0.05–4 ng of vanadium can be determined; the relative standard deviation is ca. 5% for 0.6 ng of vanadium. The toleranes for Al(III), Fe(III), Mo(VI) and iodide are 10 ng, 10 ng, 50 ng and 200 ng, respectively, for the determination of 1 ng of vanadium. About 12 samples can be injected per hour.     

Simultaneous determination of trace uranium and vanadium in biological samples by radiochemical neutron activation analysis

Summary A radiochemical neutron activation analysis (RNAA) for simultaneous determination of uranium and vanadium in a single sample at trace levels is described. The method is based on post-irradiation wet-ashing and solvent extraction of vanadium with N-benzoyl-N-phenyl-hydroxylamine reagent. From the remaining aqueous phase, uranium is extracted into a toluene solution of tri-n-butyl phosphate. The chemical yields are determined spectrophotometrically for vanadium and by gamma-counting of the added natural uranium carrier for uranium. The method was evaluated by the analysis of reference materials and the results showed a good agreement with the certified values. The method was applied to the determination of vanadium and uranium in five military total diet samples in Slovenia.     

Extraction and spectrophotometric determination of molybdenum(VI) with Malachite Green and p-chloromandelic acid

Molybdenum(VI) reacts with p-chloromandelic acid to form a complex extractable into chlorobenzene with Malachite Green, from aqueous solution at pH 2.0-4.0 at room temperature, and can then be determined indirectly by measuring the absorbance of the Malachite Green in the extract, at 630 nm. The calibation graph is linear for molybdenum over the range 0.26-10.0 x 10(-6)M (0.10-4.0 mug); the apparent molar absorptivity is 1.06 x 10(5) l.mole(-1).cm(-1). The method has been applied to the determination of molybdenum in mild steels with satisfactory results.     

Spectrophotometric determination of the oxygen to uranium ratio in uranium oxides based on dissolution in sulphuric acid

The oxygen to uranium ratio in uranium oxides such as U(3)O(8), UO(2+x) powders and UO(2) fuel pellets has been determined by a new spectrophotometric method. The method can be used for determination of O/U ratio in UO(2) pellets and powders on a routine basis. In the described method, uranium oxides in the powder form are dissolved in 2M sulphuric acid containing a few drops of HF. The concentrations of U(IV) and U(VI) are directly determined by means of the absorbances of these species at different wavelengths. For determination of the O/U ratio in U(3)O(8) powder samples, 630 and 310 nm are the wavelengths chosen for U(IV) and U(VI), respectively. For UO(2+x) powder, where the O/U ratio lies between 2.04 to 2.15, U(IV) and U(VI) are determined at 630 and 300 nm respectively, whereas for UO(2) fuel pellets, where the O/U ratio is less than 2.01, 535 and 285 nm are used. The molar absorptivity of U(IV) at 630 and 535 nm is 21.4 and 6.8 l.mole(-1).cm(-1) and that of U(VI) at 310, 300 and 285 nm is 178.1, 278.6 and 585 l.mole(-1).cm(-1), respectively. Standard deviations of +/-0.002 O/U ratio units for pellets and +/-0.004 O/U ratio units for powders have been achieved.     

Comparative study of the masking effect of various complexans in the spectrophotometric determination of uranium with arsenazo III and chlorophosphonazo III

Results are presented for the masking of 35 elements with the complexans DTPA, EGTA and TTHA in the spectrophotometric determination of uranium(VI) with Arsenazo III at pH 1.8 +/- 0.2 and with Chlorophosphonazo III at pH 1.1 +/- 0.2. The complexans EDTA and DCTA were found to be less suitable because at low pH they tended to precipitate. DTPA is shown to be especially attractive for masking other elements in the determination of uranium(VI) at low pH.     

Spectrophotometric procedure for the determination of uranium with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol at a nuclear reprocessing facility

A simple method for the determination of uranium in process- and waste-stream samples at a nuclear fuel reprocessing facility that can be applied entirely in a remote environment is described. The method is both sensitive and selective enough to be applicable for almost any uranium determination. Uranium in aqueous samples is extracted as a nitrate complex into 4-methylpentan-2-one (hexone) from an acid-deficient aluminium nitrate salting solution. An aliquot of the hexone extract is then mixed with a solution containing methanol, pyridine and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The absorbance of the U(VI)-Br- PADAP complex is measured at 580 nm. The detection limit for uranium is 0.8 μg with the linear range extending to 80 μg. Interference studies, modifications for organic samples and solid-containing samples and process laboratory data are presented.     

Determination of uranium, iron, copper, and nickel in rock and water samples by MEKC

A micellar electrokinetic capillary chromatographic (MEKC) procedure has been developed for the separation and determination of dioxouranium (VI), iron(III), copper(II), and nickel(II) using bis(salicylaldehyde)propylenediimine (H2SA2Pn) as chelating reagent with a total run time of <3 min. Sodium dodecyl sulphate (SDS) was used as micellar medium at pH 8.1 with sodium tetraborate buffer (0.1 M). Uncoated fused silica capillary with effective length 38.8 cmx75 microm id was used with an applied voltage of 30 kV and photo-diode array detection at 228 nm. Linear calibrations were established within 0.045-1000 microg/mL of each element with detection limit within 15-122 ng/mL. The method was applied to the analysis of spring water and rock samples. The presence of uranium in rock and spring water samples was established within 1.58-1739.3 microg/g and 0.047-0.712 microg/mL with relative standard deviation within 0.9-2.1% and 1.3-2.6% respectively. Uranium ore and water samples were also assayed by the standard addition technique. Recovery of uranium was >98% with RSD up to 2.7%. Copper, nickel, and iron in their combined matrix were concurrently determined within RSD 0.6-3.6% (n=5) and the results obtained were compared with those of flame AAS.     

Extraction and separation of uranium(VI) and protactinium(V) with 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone

Summary The extraction of uranium(VI) from aqueous hydrochloric or nitric acid, and the extraction of protactinium from hydrochloric acid by 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone (HY) dissolved in chloroform has been studied. At pH >4, uranium (VI) is quantitatively extracted while at pH < 1 practically all the uranium remains in the aqueous phase. At hydrochloric acid concentrations lower than 1M, protactinium(V) is quantitatively extracted while at hydrochloric acid concentration higher than 5M practically all the protactinium remains in the aqueous phase. This difference in extraction of uranium and protactinium was utilized for their separation. From 0.5M hydrochloric acid, protactinium is quantitatively extracted, and separated from uranium.The composition of the extracted uranium(VI) and protactinium (V) complexes was studied. A uranium complex with the formula UO₂Y₂ · HY was isolated from the chloroform solution. The solution of this complex in chloroform has a maximum absorbance at 319 nm and the molar absorptivity is 3.1×10⁴ l · mole^–1 · cm^–1. Owing to this property uranium can be determined spectro-photometrically directly in the organic phase.

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Zusammenfassung Die Extraktion von Uran(VI) aus wäßriger Salzsäure oder Salpetersäure sowie die Extraktion von Protaktinium aus Salzsäure mit 1-(4-Tolyl)-2-methyl-3-hydroxy-4-pyridon (HY) in chloroformischer Lösung wurde untersucht. Bei pH > 4 wird U(VI) quantitativ extrahiert, während bei pH < 1 praktisch alles Uran in der wäßrigen Phase bleibt. Bei Salzsäurekonzen-trationen unter 1-m wird Protaktinium (V) quantitativ extrahiert, während bei Salzsäurekonzentrationen über 5-m praktisch alles Pa in der wäßrigen Phase bleibt. Dieser Unterschied bei der Extraktion der beiden Elemente wurde für deren Trennung benützt. Pa wird aus 0,5-m Salzsäure quantitativ extrahiert und so von Uran getrennt.Die Zusammensetzung der extrahierten U (VI)- und Pa (V)-Komplexe wurde untersucht. Ein Urankomplex der Formel UO₂ · Y₂ · HY wurde aus der Chloroformlösung isoliert. Die Lösung dieses Komplexes in Chloroform hat ein Absorptionsmaximum bei 319 nm und eine molare Extinktion von 3,1 · 10⁴ l · mol^–1 · cm^–1. Auf Grund dieser Eigenschaft kann Uran spektrophotometrisch direkt in der organischen Phase bestimmt werden.

     

Vanadium(III) as an analytical reagent: The titrimetric determination of iron, copper, thallium, molybdenum, uranium, vanadium, chromium and manganese

Vanadium(III) solutions can be used in direct titrations of iron(III), copper(II), thallium(III), molybdenum(VI), uranium(VI), vanadium(V), chromium(VI) and manganese(VII) in milligram amounts. The titrations are done at 70-80 degrees for iron(III), copper(II), thallium(III), molybdenum(VI) and at room temperature for vanadium(V), chromium(VI) and manganese(VII). Uranium(VI) is titrated at 70-80 degrees in presence of iron(II). The vanadium(III) solution is prepared by reduction of vanadium(V) to vanadium(IV) with sulphur dioxide, followed by addition of phosphoric acid and reduction with iodide, and is reasonably stable.     

Determination of vanadium(V) and molybdenum(VI) by means of a Landolt reaction

The determination of vanadium(V) and molybdenum(VI) by a Landolt-type reaction with bromate, iodide and ascorbic acid is reported. For the determination of vanadium(V) the molybdenum(VI) is masked with citrate-citric acid buffer, which also controls the pH. Molybdenum(VI) is determined in the presence of thiourea as masking agent for vanadium(V).     

High-performance liquid chromatographic determination of uranium using solvent extraction and bis(salicylaldehyde) tetramethylethylenediimine as complexing reagent

The reagent bis(salicylaldehyde)tetramethylethylenediimine has been used for the determination of dioxouranium(VI), based on complexation in aqueous solution at pH 6, followed by extraction in chloroform and HPLC determination on a Hypersil ODS (3 μm) column. The complex was eluted with the ternary mixture methanol-acetonitrile-water (40:30:30, v/v/v), with UV detection at 260 nm. Oxovanadium(IV), iron(III), copper(II), cobalt(II), nickel(II) and palladium(II) were completely separated and did not interfere in the determination of uranium. The linear calibration range and detection limits have been obtained. The method has been applied to the determination of uranium together with copper, iron and nickel in mineral ore samples.