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.     

Sensitive analyses of agricultural chemicals by capillary electrochromatography

Capillary electrochromatography using a monolithic matrix was employed to develop a rapid and highly efficient separation methodology for the analyses of mixtures of agrochemical importance. Using this method, ppm‐ppb detection limits for urea, carbamate, and phenoxy acid herbicides were achieved without a preconcentration technique. The detection limits were further decreased to low‐ppb levels for the same class of compounds using an on‐column preconcentration technique.     

Uranium determination at ppb levels by X-ray fluorescence after its preconcentration on polyurethane foam

A sensitive method based on the preconcentration of uranium on powdered polyurethane foam (PUF) has been developed to determinate this element in water samples by X-ray florescence. Uranium at ppb levels was sorbed as the salicylate complex on powdered PUF at pH 4.0. The resulting PUF was filtered through a filter paper and used for X-ray fluorescence measurements. For 50 μg/l of uranium the coefficient of variation for five measurements is 5% and the detection limit is 5.5 μg/l. The interference level of various ions and ligands was studied and optimum conditions were developed to determine uranium in reference materials, waste water, mine drainage, and sea water.     

Voltammetric analysis of europium at screen-printed electrodes modified with salicylamide self-assembled on mesoporous silica

Mercury-free sensors for europium (Eu(3+)) assay based on the chemical modification of screen-printed carbon electrodes (SPCEs) with self-assembled salicylamide on mesoporous silica (Sal-SAMMS) have been developed. The preconcentration of Eu(3+) at SAMMS-based sensors utilizes the binding affinity of the salicylamide and Eu(3+), accomplished at open circuit potential without electrolyte and solution de-gassing. Optimal Eu detection was obtained after 3-5 min preconcentration in Eu solution (pH 2-6), electrolysis at -0.9 V for 60 s in a new medium (0.1-0.2 M NH(4)Cl, pH 3.5), followed by a square-wave voltammetric detection of Eu in the same electrolyte. Attributed to the strong covalent bonding of the functional groups on mesoporous silica and silane cross-linking, the SAMMS-modified SPCEs with a built-in 3-electrode system can be re-used for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. A linear calibration curve was found in the range of 75 to at least 500 ppb Eu(3+) after 5 min preconcentration. The experimental detection limit was 10 ppb after 10 min preconcentration, which can be improved with increased preconcentration time. Reproducibility (% RSD) of 100 ppb Eu(2+) was 10% for a single sensor and 10% for 5 sensors, which can be improved through the precision of sensor manufacturing, in which SAMMS modification can be made in-situ.     

Solid Phase Extraction of Uranium by Naphthalene‐Methyltrioctylammonium Chloride and Arsenazo(III) Adsorbent and Subsequent Spectrophotometric Determination

A simple and effective method has been presented for the preconcentration of uranium by solid phase extraction. For this purpose arsenazo(III) supported on naphthalene‐methyltrioctylammonium chloride was used as an adsorbent and uranium solution at pH 3.5 with flow rate of 1 mL·min⁻¹ was passed through the column. Therefore, uranium‐arsenazo(III) complex was formed onto column. Uranium was quantitatively eluted with 5 mL of a 0.1% ammonium tetraphenylborate and determined by spectrophotometric method at 652 nm. Several parameters such as pH, amount of reagents, sample volume, etc. were investigated. The effect of diverse ions on the preconcentration has also been studied and the optimized conditions developed have been utilized for the trace determination of uranium. A preconcentration factor of 100 was achieved. The relative standard deviation (N=8) was 0.5% for 3 ng· mL⁻¹ of uranium. The three sigma detection limit (36) was 0.045 ng·mL⁻¹     

Electrochromatography on acrylate‐based monolith in cyclic olefin copolymer microchip: A cost‐effective and easy‐to‐use technology

This article shows that there is great interest in using an electrochromatographic microchip made of hexyl acrylate (HA) based porous monolith cast within the channel of a cyclic olefin copolymer (COC) device. The monolith is simultaneously in situ synthesized and anchored to the inner walls of the channel in less than 10 min. By appropriate choice of light intensity used during the synthesis, the separation efficiency obtained for nonpolar solutes such as polycyclic aromatic hydrocarbons (PAH) is increased up to 250 000 plates/m. The performance of this HA‐filled COC microchip was investigated for a wide range of analytes of varying nature. The reversed‐phase separation of four aflatoxins is obtained in less than 2 min. The baseline separation of a mixture of neurotransmitters including six amino acids and two catecholamines is possible thanks to the superimposition of the differences in electrophoretic mobility on the chromatographic process. The durability of the system at pH 13 allows the separation of five biogenic amines and the quantitative determination of two of them in numerous wine samples. The feasibility of on‐line preconcentration is also demonstrated. Hydrophilic surface modification of COC channel via UV‐photografting with poly(ethylene glycol) methacrylate (PEGMA) before in situ synthesis of HA, is necessary to reduce the adsorption of very hydrophobic solutes such as PAH during enrichment. The detection limit of fluoranthene is decreased down to less than 1 ppb with a preconcentration of 4.5 h on the HA‐filled PEGMA functionalized COC microchip.     

Reduction of uranium concentration in well water by Chlorella (Chlorella pyrendoidosa) a fresh water algae immobilized in calcium alginate

A great deal of research has been directed towards the problem of reduction of uranium concentration from few hundreds of ppb to less than 20 ppb, a limit of uranium in drinking water from ground water resources fixed in Dec, 2001 by US, Environmental Protection Agency. Laboratory simulated experiments were carried out for the reduction of U(VI) concentration in well water from few thousands of ppb to less than 20 ppb. Well water samples were spiked with U(IV) ranging from 1000 to 2000 ppb. The contaminated solutions were passed through a glass column containing of chlorella impregnated beads of calcium alginate. Chlorella(Chlorella pyrendoidosa), a fresh water algae, was immobilized in sodium alginate in the form of beads by using 0.2M calcium chloride solution. The solution was passed again through a charcoal solution to remove any trace of impurities. The concentration of uranium after treatment ranged from 10 to 20 ppb. The concentration of other major cations and anions in the solution were also monitored. This low cost kit was proposed for on-line removal of uranium from ground water used for drinking purposes. For taking care of waste disposal, 99-100% of the adsorbed uranium on beads was recovered by 0.1M HNO₃. The desorption results suggest that the uptake of uranium by Chlorella is a physico-chemical adsorption on the cell surface, not a biological activity. The uranium in the algal cells is coupled to the ligand, which can be easily substituted with NO₃ ^-. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of uranium concentration in water by liquid anion exchange-delayed neutron analysis

Dissolved uranium is selectively removed from 11 of filtered, acidified water using a liquid anion exchange resin (Amberlite LA-1) dissolved in 10 ml of purified kerosene. The organic phase is then analyzed by a standard delayed neutron counting technique. Yields of removed uranium are consistently greater than 90 percent over a measured concentration range of 1.0 to 100 ppb uranium. The absolute detection limit based on 11 of water is 0.06 ppb. Elemental interferences are minimal and the results compare favorably with fluorometric analyses of natural waters.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

天然水中痕量铜的荧光测定

8-苯胺基-1-萘磺酸(ANS)可作为蛋白质研究的荧光探针^[1~3],ANS与可溶性的聚乙烯亚胺在微酸性溶液中以缔合物的形式结合,产生强烈的荧光并使ANS在水中的荧光激发和发射光谱分别产生红移和紫移,斯托克斯位移减小.当有痕量铜存在时,聚乙烯亚胺将与铜离子键合成聚合阳离子,它同ANS阴离子生成离子对后,由于ANS微环境极性的增强,导致荧光熄灭^[4],利用这一性质将水中痕量和超痕量的铜用巯基棉分离富集后进行测定,获得了满意结果,铜的检测下限为4.7ppb,对5至100ppb含量范围内铜的测定,相对标准偏不大于2.0%。     

Adsorptive Stripping Voltammetric Determination of Trace Uranium with a Bismuth‐Film Electrode Based on the U(VI)→U(V) Reduction Step of the Uranium‐Cupferron Complex

This work reports the use of adsorptive stripping voltammetry (AdSV) for the determination of uranium on a preplated rotating‐disk bismuth‐film electrode (BiFE). The principle of the method relied on the complexation of U(VI) ions with cupferron and the subsequent adsorptive accumulation of the complex on the surface of the BiFE. The uranium in the accumulated complex was then reduced by means of a cathodic voltammetric scan while the analytically useful U(VI)→U(V) reduction signal was monitored. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3σ limit of detection for uranium was 0.1 μg L^?1 at a preconcentration time of 480 s and the relative standard deviation was 4.7% at the 5 μg L^?1 level for a preconcentration time of 120 s (n=8). The accuracy of the method was established by analyzing a reference sea water sample.     

High‐Sensitivity Determination of Lead(II) and Cadmium(II) Based on the CNTs‐PSS/Bi Composite Film Electrode

A high‐sensitivity sensing platform for lead(II) and cadmium(II) based on the bismuth modified carbon nanotubes (CNTs)‐poly(sodium 4‐styrenesulfonate) composite film electrode (CNTs‐PSS/Bi) was fabricated. The composite film CNTs‐PSS/Bi provided remarkably improved sensitivity and reproducibility compared with previously reported CNTs‐modified electrodes. The detection limits were estimated to be 0.04 ppb for lead(II) and 0.02 ppb for cadmium(II) with a preconcentration time of 120 s, respectively. The linear responses of Cd²⁺ and Pb²⁺ were over the ranges of 0.5–50 ppb and 0.5–90 ppb, respectively. Finally, the practical application of the proposed method was verified in the real water sample with satisfactory results.     

Differential pulse voltammetric determination of uranium in low concentration streams

A differential pulse voltammetric method has been successfully used for the determination of uranium in low concentration streams of a uranium plant. The method gives a precision of about 13% to 7% in the range of 300 ppb to 15 ppm. The accuracy of the results was ascertained by comparing the values with those obtained by a spectrophotometric method. The method is simple, fast, sensitive, fairly accurate and does not require a preconcentration step.     

Column-switching RPLC for the trace-level determination of ethylenethiourea in aqueous samples

Summary Column-switching with two C18 separation columns combined with UV detection at 233 nm has been used to determine ETU in ground water samples. The direct assay of ETU (limit of detection, 1 ppb) takes less than 10 min. For the determination of ETU down to a level of 0.1 ppb, preconcentration of ETU is achieved by a liquid-liquid extraction procedure allowing the analysis of at least 12 water samples per day.For both methods (1-ppb and 0.1-ppb level), the overall recovery (96 and 82%), the repeatability (4.5 and 4.3%) and the reproducibility (5.0 and 7.9%) are satisfactory (n=18 and 28, respectively). More than one hundred samples of ground water were analysed during a 10-month period; over 0.1 ppb of ETU (range, 0.1–300 ppb) was found in 30% of the samples tested.     

Quinoline-8-ol-immobilized Amberlite XAD-4: synthesis,characterization, and uranyl ion uptake properties suitable for analytical applications

Amberlite XAD-4 has been functionalized by coupling it with 5-aminoquinoline-8-ol after acetylation. The resulting resin has been characterized by elemental analysis and IR spectra and has been used for preconcentrating uranyl ions prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption is 4-6, and desorption can be achieved by using 5 mL of 1 mol L(-1) HCl. The sorption capacity of the resin is 11.5 mmol g(-1). The effect of various cations and anions on the preconcentration of uranium in conjunction with the determination procedure has been studied and we have found that none of the ions interfere except thorium. The enrichment factor for preconcentration of uranium was found to be 200. Ten replicate determinations of 40 micro g of uranium present in 1 L of sample gave a mean absorbance of 0.185 with a relative standard deviation of 2.64%. The detection limit corresponding to three times the standard deviation of the bank was found to be 2 micro g L(-1). The validation of the developed preconcentration procedure was carried out by successfully analyzing standard marine sediment reference material. The uranyl content of sediment and soils is estimated by spectrophotometry after its preconcentration with the above chelating resin.     

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.     

Determination of uranium in seawater by flow-injection preconcentration on dodecylamidoxime-impregnated resin and spectrophotometric detection

A flow injection method has been developed for the determination of uranium in seawater combining the on-line preconcentration with spectrophotometric detection. An aliquot (10 mL) of the seawater sample adjusted to pH 5.5 was injected into the analytical system and uranium was adsorbed on the column packed with styrene-divinylbenzene copolymer resin (Bio-Beads SM-2) modified with dodecylamidoxime which showed high selectivity to uranium. Uranium was then eluted with 0.01 M hydrochloric acid and detected spectrophotometrically after the reaction with Chlorophosphonazo III. Interference from calcium and strontium was masked with cyclohexanediaminetetraacetic acid added to the chromogenic reagent solution. The sample throughput, the detection limit (3σ), and the preconcentration factor were 23 per hour, 0.13 μg/L, and 20, respectively, when the sample injection volume was kept at 10 mL. The precision at the 2 μg/L level was less than 4% (RSD). The proposed method was applied to the determination of uranium in the seawater samples collected off the Boso peninsula, Japan and the uranium concentration was found to be ca. 3 μg/L, which is close to the literature data. The yield of the recovery test ranged from 95% to 99%.     

Voltammetric detection of lead(II) and mercury(II) using a carbon paste electrode modified with thiol self-assembled monolayer on mesoporous silica (SAMMS)

The anodic stripping voltammetry at a carbon paste electrode modified with thiol terminated self-assembled monolayer on mesoporous silica (SH-SAMMS) provides a new sensor for simultaneous detection of lead (Pb2+) and mercury (Hg2+) in aqueous solutions. The overall analysis involved a two-step procedure: an accumulation step at open circuit, followed by medium exchange to a pure electrolyte solution for the stripping analysis. Factors affecting the performance of the SH-SAMMS modified electrodes were investigated, including electrode activation and regeneration, electrode composition, preconcentration time, electrolysis time, and composition of electrolysis and stripping media. The most sensitive and reliable electrode contained 20% SH-SAMMS and 80% carbon paste. The optimal operating conditions were a sequence with a 2 min preconcentration period, then a 60 s electrolysis period of the preconcentrated species in 0.2 M nitric acid, followed by square wave anodic stripping voltammetry from -1.0 V to 0.6 V in 0.2 M nitric acid. The areas of the peak responses were linear with respect to metal ion concentrations in the ranges of 10-1500 ppb Pb2+ and 20-1600 ppb Hg2+. The detection limits for Pb2+ and Hg2+ were 0.5 ppb Pb2+ and 3 ppb Hg2+ after a 20 min preconcentration period.     

Fast sensitive analysis of uranium and thorium in natural samples based on delayed neutron counting using an ultrafast conveyor tube system

A fast, sensitive and routine methode for quantitative analysis of uranium and thorium in natural samples is described. The identification is done by counting the delayed neutrons of mainly the short living fission products after sample-irradiation with and without cadmium shielding. The rabbit system used is installed at the Forschungsreaktor Neuherberg, type TRIGA Mark III. The limits of detection (relative to 2 g of sample weight) were specified to be 20 ppb (U) and 3 ppm (Th) using puls irradiations, 150 ppb (U) and 15 ppm (Th) using 1 MW steady state reactor power. A single determination is done within less than 60 s. The methods were proved by about 3000 measurements also including comparison experiments.     

Analytical procedures for the determination of uranium and thorium traces in aluminium

Summary Different combined procedures involving element preconcentration and ICP-OES or polarography are described for the determination of the alpha emitters uranium and thorium in aluminium. The results are compared with those of instrumental neutron activation analysis.After extraction with ethyl acetate, uranium and thorium can be determined by ICP-OES (uranium detection limit, given as 3so, 12 ng/g, standard deviation 0.95 ng/g at 12.5 ng/g; thorium detection limit 8 ng/g, standard deviation 0.9 ng/g at 12.5 ng/g). After a second extraction with tri-n-octyl phosphine oxide, uranium can be determined by polarography (detection limit 10 ng/g, standard deviation 4.4 ng/g at 200 ng/g). Thorium also can be coprecipitated with Fe(OH)₃ and determined with ICP-OES (detection limit 5 ng/g, standard deviation 0.6 ng/g at 10 ng/g).The results obtained by wet chemical analyses lie within the spread of accuracy of the INAA results obtained by several laboratories. In general, the comparative results indicate that super pure aluminium containing less than 1 ng/g uranium and thorium can be produced.The paper has been presented at 12th Colloquium on Materials Analysis, Institute for Analytical Chemistry, Technical University in Vienna, May 13–15, 1985.