A separation method to overcome the interference of calcium on the uranium determination by ICP-ES

The accurate determination of uranium by Inductively Coupled Plasma Emission Spectrometry (ICP-ES) in calcium phosphate matrix suffers from a severe ionization interference due to the high calcium content of the samples. This leads to a signal depression up to 30%. For reliable determinations an extraction method based on anion exchange resin column chromatography is described which separates uranium for the needs in ICP-ES measurements. The results are comparable with results obtained by other determination methods. In addition, reference materials were measured to verify this extraction procedure.     

A spectrophotometric method for uranium determination

A very sensitive extraction spectrophotometric method for the analysis of uranium based on the extraction of a uranium—benzoate—crystal violet complex by a mixture of xylene and benzene is described. The absorbance maximum is at 606 nm and molar absorptivity is 4.28·10⁴ l·mol⁻¹·cm⁻¹. The interference due to a number of anions and cations studied without any pre-extraction was found to be within permissible limits. The method has been used for determining uranium in a synthetic solution, i.e., uranium in the presence of various other ions. The interference due to some cations was eliminated by the use of a masking agent (boric acid).     

A potentiometric method for the determination of uranium by stannous chloride reduction

A potentiometric method has been developed for the determination of uranium using stannous chloride as reductant. The oxidation of excess stannous chloride was accomplished with an excess of sodium nitrite, the excess of which was destroyed by sulfamic acid. The U(IV) was then determined by potentiometric titration with standard potassium dichromate. For 3–5 mg amounts of uranium the precision obtained was better than 0.3%.     

Influence of digestion methods on the determination of total Al in food samples by ICP-ES

Summary To determine total Al in a variety of food and total diet samples using ICP-ES, HF pre-treatment, prior to wet digestion (HNO₃/HClO₄) seems to be necessary. Compared with results obtained after HF pre-treatment, the determination of Al using pressure microwave digestion with HNO₃ or HNO₃/HClO₄ digestion recovered only between 25–50% Al for dried spinach and flour and 40–75% for total diet samples, respectively. In most cases the addition of 0.25 ml HF (40%) per gram dry mass resulted in maximum Al yield. The results are in acceptable agreement with those obtained by neutron activation analysis (NAA).     

A novel method for the determination of a PCB sum value by enzyme immunoassay to overcome the cross-reactivity problem

Many attempts have been made to detect polychlorinated biphenyls (PCBs) by enzyme immunoassay (ELISA). All known ELISAs to PCBs show characteristic cross-reactivity problems. Without any prior information about the composition of the sample, no quantification of the total PCB content is possible. A chemical approach is shown to solve the cross-reactivity problem by the quantitative dechlorination of all PCB congeners to the single compound biphenyl. For the reductive dechlorination palladium on barium sulfate and ammonium formate were used. The dechlorination procedure was optimized to be performed at room temperature in methanol without the exclusion of oxygen or water. For the development of polyclonal biphenyl-antibodies the synthesis of the hapten biphenylhexanoic acid via Grignard cross-coupling is described and an immunization protocol is given. The purity of the used immunological reagents proved to be very crucial. The whole procedure was tested with spiked soil samples. The detection limit for PCBs (Clophen A50) in soil was 1 mg/kg (3.1 μmol/kg). This corresponds to a biphenyl concentration in methanol of 0.1 mg/L (0.6 μmol/L).     

A novel method for the determination of a PCB sum value by enzyme immunoassay to overcome the cross-reactivity problem

Many attempts have been made to detect polychlorinated biphenyls (PCBs) by enzyme immunoassay (ELISA). All known ELISAs to PCBs show characteristic cross-reactivity problems. Without any prior information about the composition of the sample, no quantification of the total PCB content is possible. A chemical approach is shown to solve the cross-reactivity problem by the quantitative dechlorination of all PCB congeners to the single compound biphenyl. For the reductive dechlorination palladium on barium sulfate and ammonium formate were used. The dechlorination procedure was optimized to be performed at room temperature in methanol without the exclusion of oxygen or water. For the development of polyclonal biphenyl-antibodies the synthesis of the hapten biphenylhexanoic acid via Grignard cross-coupling is described and an immunization protocol is given. The purity of the used immunological reagents proved to be very crucial. The whole procedure was tested with spiked soil samples. The detection limit for PCBs (Clophen A50) in soil was 1 mg/kg (3.1 μmol/kg). This corresponds to a biphenyl concentration in methanol of 0.1 mg/L (0.6 μmol/L). Received: 25 September 1998 / Revised: 1 December 1998 / Accepted: 4 December 1998     

The spectrophotometric determination of uranium by the 1-pyrrolidinecarbodithioate method

Summary A spectrophotometric method for the determination of uranyl ion is proposed which is based on the use of ammonium 1-pyrrolidinecarbodithioate as the chromogenic reagent. Conformity to Beer's law was observed for the range between 0 to 50 ppm of uranium when spectrophotometric measurements are made at 385 nm.

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Zusammenfassung Ein spektrophotometrisches Verfahren zur Uranylbestimmung mit Ammonium-1-pyrrolidindithiocarbamat als Farbreagens wurde vorgeschlagen. Zwischen 0 und 50 ppm ist das Beersche Gesetz bei 385 nm erfüllt.

     

A specific method for the determination of uranium in ores by cathode ray polarography

A method is presented for the specific determination of uranium in ores by cathode my polarography. The uranium is separated by a simple and rapid mercury-cathode electrolysis, then determined polarographically in a base electrolyte in which vanadium, titanium and tungsten do not interfere. Application of the method to the analysis of ten standard uranium ores is shown.     

A simple method for the determination of uranium and thorium by delayed neutron counting

A simple method for the determination of uranium and thorium by delayed neutron counting is described. One portion of the sample is irradiated in a reactor and the delayed neutrons are counted. Another portion of the sample is mixed with B₄ C powder absorbing the thermal neutrons, and irradiated in the same position. From those data, both uranium and thorium can be calculated when a quantitative calibration has been made beforehand. The detection limits for the pure elements are 0.07 ppm for uranium and 2 ppm for thorium with the minimum analyzing time being 2 min. The accuracy of the method is investigated by comparing results obtained by the method described here with results obtained by epithermal activation analysis.     

A simplified determination of uranium in phosphate rock and phosphogypsum by alpha-spectroscopy after its separation by liquid-extraction

A relatively rapid, economic and robust procedure is described for the radiometric analysis of uranium in phosphate rock and phosphogypsum. The analysis is performed by alpha spectroscopy after pre-concentration and separation of uranium by liquid-extraction using tributyl-phosphate (30% TBP in dodecan) and finally its electrodeposition on stainless steel discs. The method has been successfully applied to 0.1 g samples of phosphate rock and phosphogypsum resulting in high-quality spectra for measurement times ≥15 h. The main advantage of the procedure is the use of tracer solution (²³²U) that allows reliable measurements and evaluation of the separation procedure. The separation efficiency of the proposed method has been estimated to be (75 ± 20)%.     

Gamma-spectrometric determination of uranium enrichment: A review of the method

Gamma-spectrometric determination of the uranium enrichment is reviewed and two main point are analyzed: (a) The correlation between the enrichment factor and the mass of the sample and (b) the intensity of the -ray used in the method, which had to be changed from previous works. Furthermore a X² minimization has been included into the method, improving its reliability.     

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.     

A method for the determination of the uranium content in U-Al alloys

The paper describes a method for the determination of uranium content in enriched U–Al alloys. The mass-spectrometric isotope dilution method was proposed and verified for the determination of uranium in these materials. A solution of natural uranylnitrate, prepared by dissolution of standard reference material NBS-U-960, was used as a spike. Uranium was separated from aluminium in the form of chloro complexes by sorption on anion exchange resin Dowex 1-X8 from 9M HCl. The error of determination lies in an interval 0.03–0.07% rel. for uranium contents 18.2–22.8 wt%.     

Universal method for the anion exchange separation of uranium and its application to the determination of uranium in sea water, marine sediments and other geological samples

Summary Before the fluorimetric determination of uranium in sea water, marine sediments and other geological samples an ion exchange procedure is used to separate uranium from interfering elements. This separation is best performed on Dowex 1 in a medium consisting of 90% methyl glycol and 10% 6 N hydrochloric acid. By means of this method easily reproducible and accurate results of determinations of uranium in as little as 250 ml of sea water or in about 0.1 g amounts of solid samples can be obtained. Because of its universal applicability this technique is to be recommended whenever g but also mg quantities of uranium have to be determined.

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Zusammenfassung Vor der fluorimetrischen Bestimmung von Uran in Meerwasser, Meeressedimenten und anderen geologischen Proben wird das Uran durch ein Ionenaustauschverfahren von störenden Elementen getrennt. Diese Trennung wird am besten auf Dowex l in einem Medium aus 90% Methylglykol und 10% 6 n Salzsäure ausgeführt. Mit dieser Methode lassen sich leicht reproduzierbare und genaue Uranbestimmungen im Meerwasser und in festen Proben durchführen, selbst wenn deren Mengen 250ml bzw. 0,1 g nicht überschreiten. Infolge ihrer allgemeinen Anwendbarkeit wird die Methode zur Bestimmung von g- und mg-Mengen Uran empfohlen.

     

Selective ion exchange separation of uranium from concomitant impurities in uranium materials and subsequent determination of the impurities by ICP-OES

An ion exchange method has been developed for the separation of uranium from trace level metallic impurities prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in uranium materials. Selective separation of uranium from trace level metallic impurities consisting Cr, Co, Cu, Fe, Mn, Cd, Gd, Dy, Ni, and Ca was achieved on anion exchange resin Dowex 1 × 8 in sulphate medium. The resin (100–200 mesh, in chloride form) was packed in a small Teflon column (7.8 cm × 0.8 cm I.D.) and brought into sulphate form by passing 0.2 N ammonium sulphate solution. Optimum experimental conditions including pH and concentration of sulphate in the liquid phase were investigated for the effective uptake of uranium by the column. Uranium was selectively retained on the column as anionic complex with sulphate, while impurities were passed through the column. Post column solution was collected and analyzed by ICP-OES for the determination of metallic impurities. Up to 2,500 μg/mL of uranium was retained with >99% efficiency after passing 25 mL sample through the column at pH 3. Percentage recoveries obtained for most of the metallic impurities were >95% with relative standard deviations <5%. The method established was applied for the determination of gadolinium in urania–gadolinia (UO₂–Gd₂O₃) ceramic nuclear fuel and excellent results were achieved. Solvent extraction method using tributylphosphate (TBP) as extractant was also applied for the separation of uranium in urania–gadolinia nuclear fuel samples prior to the determination of gadolinium by ICP-OES. The results obtained with the present method were found very comparable with those of the solvent extraction method.     

A new volumetric method for the determination of uranium(VI)

Summary A new volumetric method for the estimation of uranium(VI) salt based on its photoreduction in the presence of diethyl ether has been developed. The recommended procedure consists of exposing uranium(VI) solution in about 1 N sulphuric acid solution with an excess of saturated aqueous ether solution in a glass vessel to the light from a Phillips repro lamp or sun light for 1 hour. The uranium(IV) salt formed is estimated by titration with a standard solution of sodium vanadate.The reduction does not proceed to uranium(III) stage under any conditions of exposure. Fluoride, phosphate, arsenate and perchlorate are not found to interfere either with the photochemical reduction or with the subsequent oxidimetric titration. But chloride and bromide ions markedly inhibit the photochemical reaction.     

A gravimetric method for the determination of oxygen in uranium oxides and ternary uranium oxides by addition of alkaline earth compounds

A simple gravimetric determination of oxygen in uranium oxides and ternary uranium oxides is described. In alkaline earth uranates which are formed by heating in air at 800–1100°C, uranium is in the hexavalent state over certain continuous ranges of alkaline earth-to-uranium ratios. Thus, if an alkaline earth uranate or a compound containing an alkaline earth element, e.g. MgO, is mixed with the oxide sample and heated in air under suitable conditions, oxygen can be determined from the weight change before and after the reaction. The standard deviation of the O:U ratio for a UO_2+x test sample is ±0.0008–0.001, if a correction is applied for atmospheric moisture absorbed during mixing.     

A new approach to overcome natural cholesterol interference during simultaneous determination of two stable isotope-enriched cholesterol tracers in human plasma

We have developed a validated gas chromatography/mass spectrometry (GC/MS) method with two labelled cholesterol tracers, i.e. (2)H(4) ([2H4]-Chol) and (2)H(7) ([2H7]-Chol) enriched moieties, with a new way of calculating the abundance of labelled cholesterol in plasma without natural cholesterol interference. The isotopomers of the analytes could interfere during analysis. Elimination of these interferences can be performed by the blank or mathematical subtraction method. Validation was performed with the two interference elimination methods. For both methods, linearity was obtained in the range 5 x 10(-4) to 10(-2) mM for both labelled cholesterol moieties. In the same range, repeatability and reproducibility were less than 6.5% and 7.5% for [2H4]-Chol and [2H7]-Chol, respectively. Accuracy was about 100% and recoveries always included 100% for the two labelled cholesterols. We demonstrate that measurement of blank plasma is not necessary when using the validated abundance isotope calculation method. This saves time, reagent and samples. This calculation strategy can be extrapolated to comparable tracer approaches.     

ICP-AES determination of silver after chemical separation from uranium matrix

The separation of silver from a uranium matrix has been carried out using Cyanex-471X (triisobutylphosphine sulphide) in xylene. The effects of various parameters such as the Cyanex-471X concentration, the nitric acid molarity, the contact time and the nitrate ion concentration on the extraction of silver have been studied. The silver metal ion species extracted into the organic phase was found to be Ag(NO₃)·2S (where S is Cyanex-471X). The stripping of silver into an aqueous medium was carried out with 5% NaHSO₃, followed by its determination using ICP-AES.