Determination of individual rare earth elements in Vietnamese monazite by radiochemical neutron activation analysis

Radiochemical neutron activation analysis (RNAA) has been applied for determination of rare earth elements (REE) in Vietnamese monazite. The chemical separation procedure used is based on the chromatographic elution of rare earth groups, after the separation of²³³Pa(Th) in irradiated monazite samples by coprecipitation with MnO₂, the rare earth elements were retained by Biorad AG1×8 resin column in 10% 15.4M HNO₃-90% methanol solution. The elution of heavy rare earth (HREE) and middle rare earth (MREE) groups was carried out with 10% 1M HNO₃-90% methanol and 10% 0.05M HNO₃-90% methanol solution, respectively; while the light rare earths (LREE) were eluted from the column by 0.1M HNO₃ solution. The accuracy of the method was checked by the analysis of granodiorite GSP-I and the rare earth values were in good agreement.     

Separating Ag, B, Cd, Dy, Eu, and Sm in a Gd matrix using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester extraction chromatography for ICP-AES analysis

The separation procedure for Ag, B, Cd, Dy, Eu and Sm as impurities in Gd matrix using ICP-AES technique with an extraction chromatographic column has been developed. The spectral interference of the Gd matrix on the elements was eliminated using a chromatography technique with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as the mobile phase and XAD-16 resin as the stationary phase. Ag⁺, B₄O₇²⁻, and Cd²⁺ were eluted with 0.1 M HNO₃, while rare earth ions were not. The best eluent for separating Eu and Sm in the Gd matrix was 0.3 M HNO₃. The limit of quantitation for these elements was 0.6-3.0 ng mL⁻¹. The recovery of Ag, B, and Cd was 90-104% using 0.1 M HNO₃ as the eluent, while that of Eu, Gd, and Sm ranged from 100 to 102% with 0.3 M HNO₃. Dy was recovered quantitatively with 4 M HNO₃. The relative standard deviation of the methods for a set of three replicates was between 1.0 and 15.4% for the synthetic and standard Gd solutions. The proposed separation procedure was used to measure Ag, B, Cd, Dy, Eu, and Sm in a standard Gd solution.     

Neutron activation analysis for determination of cerium trace impurity in high purity lanthanum oxide

Cerium trace impurity in high purity lanthanum oxide (99.99%) has been determined by NAA after pre-separation of La matrix. In this method, the sample was dissolved in conc. nitric acid and diluted with water. The final concentration of solution is about 0.1M of nitric acid. It was passed through a MnO₂ column. Under these conditions cerium is retained on the column quantitatively without retaining lathanum. Cerium is eluted with 4M nitric acid. The recoveries of Ce were checked with tracers and by standard addition to lanthanum oxide matrices. Results obtained on a high purity lanthanum oxide are reported here.     

Carbon Nanofibers as Solid‐Phase Extraction Adsorbent for the Preconcentration of Trace Rare Earth Elements and Their Determination by Inductively Coupled Plasma Mass Spectrometry

Abstract

Systematic investigations were carried out into the sorption of rare earth elements (REEs) on carbon nonofibers (CNFs) by inductively coupled plasma mass spectrometry (ICP‐MS). The experimental parameters for preconcentration of REEs, such as pH, sample flow rate and volume, eluent concentration, and interfering ions on preconcentration of REEs have been examined in detail. The studied metal ions can be adsorbed quantitatively on CNFs in a pH range from 2.0 to 5.0, and then eluted completely with 0.5 mol l^?1 HNO₃. Based on the above facts, a novel method using a microcolumn packed with carbon nanofibers as an adsorption material was developed for the separation and preconcentration of REEs prior to their determination by ICP‐MS. The proposed method has been successfully applied to the determination of light (La), medium (Eu and Gd) and heavy (Yb) rare earth elements in real sample with the recovery more than 90%. In order to validate this method, two certified reference materials of tea leaves (GBW 07605) and mussel (GBW 08571) were analyzed, and the determined values are in good agreement with the certified values.     

Trace element analysis of high purity arsenic through vapour phase dissolution and ICP-QMS

Vapour phase dissolution (VPD) has been used for the dissolution of high purity arsenic through acid vapours generated by aquaregia mixture, prior to trace element characterization. Trace impurities in As were determined by employing ion-exchange and volatilization methodologies for quantitative separation of the As matrix. After dissolving the As matrix through VPD procedure, sample solution in 0.1 M HF medium was loaded on Dowex-50WX8. The sorbed elements were then eluted first with a 20 ml aliquot of 4 M HNO₃ followed by another 10 ml of 6 M HNO₃ for the elution of REE (La, Ce, Gd and Lu). In the volatilization procedure, arsenic was removed from H₂SO₄ medium as volatile bromide by three successive additions of HBr at a temperature of about 220 °C. The trace element determinations were carried out by ICP-QMS. In both the matrix separation procedures namely on Dowex-50WX8 in 0.1 M HF medium and volatilization from H₂SO₄+HBr medium showed that the removal of arsenic matrix was nearly quantitative (>99.99%). The recoveries of trace elements were found to be >95%. Good agreement was obtained for many elements in both the procedures. The VPD approach provides considerable reduction of the process blank levels for all the elements when compared with conventional open dissolution approach. The subsequent ion-exchange or volatilization steps, contribute more to the overall process blanks.     

Composite ion exchanger for removal of sodium-24 from mineralizates of biological materials in neutron activation analysis

A composite ion exchanger containing hydrated antimony pentoxide (HAP) in polystyrene-divinylbenzene matrix has been prepared. Its sorption properties with respect to Na, As, Au, Cd, Cu, Ga, Hg, In, K, La, Mn, Mo (Tc), Pd, Pt, Sb, W and Zn have been examined. Sodium is quantitatively retained on the sorbent from 8M HCl solution as well as from a mixture of conc. H₂SO₄+ conc. HNO₃+H₂O (1+1+2). As, W, Cd and Sb are partially retained, while the remaining elements are not retained and can be quantitatively eluted. The composite ion exchanger is stable to oxidizing acid media and it can be directly applied to separation of²⁴Na from mineralizates of neutron-irradiated biological materials.     

Determination of Rare earth elements in environmental samples by solid phase extraction ICP OES

A simple sample pre-treatment method for rare earth elements enrichment from environmental water samples prior to optical emission spectrometry determination with inductively coupled plasma (ICP OES) is proposed based on solid phase extraction with octadecyl silica gel modified with 1,2,5,8-tetrahydroxyanthraquinone. Optimal experimental conditions including pH of sample solution, sample volume, type, concentration and volume of eluent were investigated and established. Rare earth elements ions were quantitatively adsorbed from aqueous solution onto octadecyl silica gel modified with Quinalizarin at pH 7.0. The adsorbed ions were eluted with 1.0 mL of 2 M HNO₃ and simultaneously determined by ICP OES. Under obtained optimum conditions the calibration curves were linear with the coefficient of variation better than 0.99. The limit of detection of the method for the studied elements was in the range of 0.0004–0.01 ng/mL. The proposed method has a pre-concentration factor of 320–450 in water samples, which results in high sensitivity detection of trace ions. The developed method gave recoveries better than 80% and RSDs less than 15%.     

Craig-Verteilung von Seltenerdnitraten im System Tri-n-butylphosphat—Salpetersäure, 1. Mitt: Trennung von Ceriterdgemischen

Zusammenfassung Die multiplikative Verteilung von Ceriterdgemischen zwischen HNO₃ und Tri-n-butylphosphat wurde in einer 40-bzw. 60stufigenCraig-Apparatur vom präparativen Standpunkt untersucht. Beim Durchsatz von Mengen um 50 g konnten bei unsymmetrischer zweiphasiger Entnahme bis zu 50% des eingesetzten Gemisches mit einer Reinheit über 90 bzw. 99% erhalten werden. Der Einfluß der verschiedenen Variablen auf die Trennung wird besprochen.

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Craig-distribution of rare earth nitrates in the system tri-n-butyl phosphate-HNO ₃, I: Separation of cerium earth mixtures

The fractionation of cerium-group rare earth mixtures was studied from a preparative point of view using fractional distribution between HNO₃ and tri-n-butyl phosphate in aCraig-apparatus (40 and 60 stages, resp.). When processing ca. 50 g and using the unsymmetrical double withdrawal method up to 50% of the input could be extracted in a purity of better than 90 and 99%, resp. The influence of certain variables upon fractionation is discussed.

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Mit 1 Abbildung     

Determination of radioactive strontium in seawater

This paper describes the procedures of isolating strontium and yttrium from seawater that enable the determination of ^89,90Sr. In one procedure, strontium is directly isolated from seawater on the column filled with Sr resin by binding of strontium to the resin from 3 M HNO₃ in a seawater, and successive elution with HNO₃. In others, strontium is precipitated from seawater with (NH₄)₂CO₃, followed by isolation on a Sr column or an anion exchange column. It is shown that strontium precipitation is optimal with concentration of 0.3 M (NH₄)₂CO₃ at pH = 11. In these conditions, 100% Y, 78% Sr, 80% Ca and 50% Mg are precipitated. Strontium is bound on to Sr column from 5 to 8 M HNO₃, separated from other elements by elution with 3 M HNO₃ and 0.05 M HNO₃. Strontium and yttrium are bound on to anion exchange column from alcoholic solutions of nitric acid. The optimum mixture of alcohols for sample binding is a mixture of ethanol and methanol with the volume ratio 1:3. Strontium and yttrium are separated from Mg, Ca, K, and other elements by elution with 0.25 M HNO₃ in the mixture of ethanol and methanol. After the separation, yttrium and strontium are eluted from the column with water or methanol.In the procedure of direct isolation from 1 l of the sample, the average recovery of 50% was obtained. In the remaining two procedures, the strontium recovery was about 60% for the Sr column and 65% for anion exchange column. Recovery of yttrium is about 70% for the anion exchange column. It turned out that the procedure with the Sr resin (direct isolation and isolation after precipitation) is simpler and faster in the phase of the isolation on the column in comparison with the procedure with the anion exchanger. The procedure with the anion exchanger, however, enables the simultaneous isolation of yttrium and strontium and rapid determination of ^89,90Sr. These procedures were tested by determination of ^89,90Sr on liquid scintillation counter and Cherenkov counting in 5 M HNO₃. Obtained results showed that activity of 50 mBq l⁻¹ of ^89,90Sr and higher can be simultaneously determined.     

Spectrometry: Speciation of Parts PER Billion of Metal Ions Using Silica and C18-Bonded Silica Columns and Graphite Furnace Atomic Absorption Spectrometry

Abstract

It is demonstrated that silica gel columns will quantitatively adsorb free Cu²⁺ and Pb²⁺ ions at pH > 8. These are eluted with 0.1 M HNO₃ but not with methanol. Negatively charged EDTA chelates are not adsorbed. Neutral APDC chelates are partially adsorbed on silica columns, but are quantitatively adsorbed on C18-bonded columns, and are eluted with methanol. The metal ions are partially adsorbed on C18-bonded columns, due to residual silanol groups. A microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer, using either methanol or 0.1 M HNO₃ in methanol eluant, allowing speciation and measurement of parts per billion of metals. These studies demonstrate that by using a mixed column or sequential columns of silica gel and C18-bonded silica, cationic and neutral metal species could be adsorbed, followed by sequential elution and measurement using methanol and then 0.1 M HNO. Negatively charged species could be measured directly in the sample eluant or obtained by difference from a total metal measurement.     

Rapid Separation of Plutonium in Environmental Samples Using an Anion Exchange Resin Disk

A rapid analytical method of Pu in environmental samples by alpha-ray spectrometry and high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) using a 3M Empore anion exchange resin disk for solid phase extraction has been developed. A trace amount of Pu was quantitatively adsorbed with an Empore anion exchange resin disk (47 mm diam.) at a flow rate of 150–200 ml/min from 8M HNO₃ sample solution. The disk was washed with 10 ml of 8M HNO₃ and 12 ml of 9M HCl and then the Pu was quantitatively eluted with 15 ml of 1M HNO₃/0.03M ascorbic acid solution. The time needed to separate Pu from the sample solution with the present method was about 20 minutes. The separated Pu was determined with alpha-ray spectrometry and HR-ICP-MS. The present method was applied to the determination of Pu in the certified reference material (IAEA-135) and the environmental soil sample. The analytical results were almost in good agreement with the literature values.     

Anion exchange separation of the light lanthanoids with nitric acid-methyl alcohol mixed media at elevated temperature

Anion exchange chromatography with nitric acid-methyl alcohol mixed media at elevated temperature has been applied to mutual separation of the light lanthanoids, La, Ce, Pr, Nd and Pm. The individual elements could be effectively separated from each other, main fission products and actinoids with 0.01M HNO₃-90% CH₃OH or 0.5M HNO₃-80% CH₃OH eluent at 90 °C.     

Statistical mixture design development of digestion methods for Oyster tissue using inductively coupled plasma optical emission spectrometry for the determination of metallic ions

The quantitative determination of chemical elements in organic or biological samples is an important analytical problem. Normally the elements to be determined in the organic matrix must be transformed into a simple inorganic form. A digestion method by heating on a block digestor has been developed for the determination of Al, As, Ba, Ca, Cd, Co, Cu, Fe, Mg, Mn, V and Zn in Oyster tissue by ICP OES. A simplex centroid statistical mixture design has been used to study the effects of changing HNO₃, HCl and H₂O₂ reagent proportions on the digestion of these samples. Response surface and principal component analyses show that the species Ca, Cd, Cu, Fe, Mg, Mn and Zn have very similar analytical tendencies under this experiment. By means of mixture modeling maximum recoveries for these ions were predicted using 19%, 18% and 63% of the HCl, HNO₃ and H₂O₂ pseudocomponent mixtures, respectively. This corresponds to 21.4%, 30.8% and 47.8% of the HCl, HNO₃ and H₂O₂ commercial solutions. Furthermore the As, Co and V ions present large recoveries for these mixtures as well. The Al and Ba ion recoveries are seen to be independent of the mixture proportions. The analysis of Oyster tissue reference material (SRM 1566b - NIST) under optimized conditions at the selected wavelengths resulted in ion recoveries between 90% and 100%.     

Application of ICP-AES to the determination of rare earth elements in phosphate samples

Summary ICP-AES has been used for the determination of rare earth elements (REE) in samples of phosphorite deposits collected from the Western Desert, Egypt. Complete dissolution of the samples was achieved by using acid digestion with HF/HNO₃/HCl in a PTFE closed vessel and subsequent treatment with HClO₄, with the same procedure but with fuming HCl replacing HClO₄ and with HNO₃ and fuming HCl in a quartz vessel and subsequent treatment with HF/HClO₄/HNO₃. Analysis lines for La, Ce, Pr, Nd, Sm, Gd, Dy and Y were selected after study of the spectral interferences for the sample types concerned. Results revealed that the average total content of the REE, which could be directly determined in the present samples, varies between 1.08 and 1.53 mg/g, whereas individual element concentrations range from 40 to 300 g/g. Analysis results obtained with the different dissolution techniques were found to be in good agreement. On leave from the National Research Centre, Physics Department — Spectroscopy Laboratory, Cairo, Egypt     

Separation of140Ba−140La by reversed phase chromatography using high molecular weight amine

A method has been described for the isolation of radiochemically pure¹⁴⁰La from¹⁴⁰Ba. The tracer¹⁴⁰Ba−¹⁴⁰La is mixed with 6M LiNO₃ solution to make an anionic complex. The solution is then fed into a column (1 cm×0.4 cm) of Kieselguhr impregnated with Aliquat-336.¹⁴⁰La is adsorbed in the column while¹⁴⁰Ba is eluted with 6M LiNO₃. After complete removal of¹⁴⁰Ba,¹⁴⁰La is eluted with 0.002M HNO₃ solution. The purity of¹⁴⁰La is established by both its half-life and γ-spectrum.     

Separation of uranium from thorium on cryptomelane-type hydrous manganese dioxide

The distribution of UO ₂ ²⁺ and Th⁴⁺ in nitric acid media on crypomelane-type hydrous manganese dioxide (CRYMO) has been investigated by batch equilibrations and column break-through techniques. The parameters studied involve the media composition and concentrations of HNO₃, NaNO₃, UO ₂ ²⁺ and Th⁴⁺. It is found that Th⁴⁺ is more strongly adsorbed on CRYMO than UO ₂ ²⁺ with sufficient differences for chromatographic separation from each other. Uranium was quantitatively eluted from a CRYMO column with 0.1M HNO₃. Th⁴⁺ has been recovered by using 1M HNO₃ as eluent.     

Selectivity of glassy type mixed zirconium-titanium phosphate toward rare earth metal ions

The selectivity of glass type mixed Zr+Ti phosphates with various Ti contents has been investigated toward rare earth metal ions. The k_d values were determined by radiotracer technique both in HCl and HNO₃ solutions of various concentrations. At room temperature and at pH=4 the following selectivity orders were found: Yb>TmEu>Sm>La (HCl) and Eu>La>Sm>Yb>Tm (HNO₃).     

Determination of trace rare earth elements by inductively coupled plasma atomic emission spectrometry after preconcentration with multiwalled carbon nanotubes

A new method has been developed for the determination of trace rare earth elements (REEs) in water samples based on preconcentration with a microcolumn packed with multiwalled carbon nanotubes (MWNTs) prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimum experimental parameters for preconcentration of REEs, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been investigated. The studied REEs ions can be quantitatively retained by MWNTs when the pH exceed 3.0, and then eluted completely with 1.0 mol L⁻¹ HNO₃. The detection limits of this method for REEs was between 3 and 57 ng L⁻¹, and the relative standard deviations (RSDs) for the determination of REEs at 10 ng mL⁻¹ level were found to be less than 6% when processing 100 mL sample solution. The method was validated using a certified reference material, and has been successfully applied for the determination of trace rare earth elements in lake water and synthetic seawater with satisfactory results.     

Simultaneous production and separation of no-carrier-added 111In, 109Cd from alpha particle induced silver target

A natural silver foil was bombarded by 30 MeV α-particles which produced ¹¹¹In, ¹⁰⁹Cd and ^106mAg in the target matrix. ¹¹¹In and ¹⁰⁹Cd were separated from the Ag target matrix employing ion-exchange chromatography and liquid–liquid extraction (LLX). In the chromatographic separation, the active solution containing the NCA products were adsorbed in the column containing Dowex 50 and were eluted with HNO₃. Bulk silver and ¹⁰⁹Cd were sequentially eluted with 1 M HNO₃. After complete elution of ¹⁰⁹Cd and the bulk, ¹¹¹In was eluted with 1.5 M HNO₃. In the LLX, the NCA ¹¹¹In was extracted to 1 % HDEHP (di-2(ethylhexyl)phosphoric acid) from 10^?2 M HNO₃ solution, leaving cadmium and bulk silver quantitatively in the aqueous phase. The NCA ¹⁰⁹Cd was separated from the bulk Ag by precipitating Ag as AgCl. NCA ¹¹¹In was stripped back quantitatively from HDEHP phase using 8 M HNO₃.     

Determination of the Average Oxidation Degree of Manganese in Single Crystals of Manganites

A procedure has been developed for the determination of the average oxidation degree of manganese in manganites of rare-earth elements. It is shown that potassium periodate in a mixture of conc. HNO₃and H₃PO₄quantitatively oxidizes manganites to permanganic acid at a temperature of 90°C. This allows total manganese in a test sample to be determined by photometry. The procedure involves two independent steps at which the average oxidation degree of manganese in manganites is determined by photometry and iodometry with a confidence interval of 0.02.