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     

Determination of rare earths and other trace elements in samples of Antarctica by neutron activation analysis

The concentrations of REE and other trace elements have been determined in samples of Antarctica by Instrumental Neutron Activation Analysis (INAA). The samples were collected from the West Lake area near Great Wall Station. The samples include sediment, residual plants, rock and soil taken from the bottom of the lake to 3.4 m deep. The amounts of samples were very rare. In order to get more information, reactor NAA using both short and long irradiations with K₀ standardization has been adopted. Nine rare-earth elements (REE) namely La, Ce, Nd, Sm, Eu, Tb, Dy, Yb, and Lu as well as other trace elements (As, Au, Ba, Br, Co, Cr, Hf, Sc, Se, Th, V, Zn) have been determined. The concentrations and distribution patterns of REE in the samples have been given.     

Determination of rare earth and other trace element abundances in human kidney stones and brain tissue by instrumental neutron activation analysis

We have used INAA to analyze more than 30 minor and trace elements in 10 human kidney stones (phosphate and oxalate types). In addition we also analyzed human brain tissue samples for trace elements by INAA to determine the limitations of the method. Samples were taken from the temporal and frontal cortex of the brain of a patient that suffered from dialysis encephalopathy (where an increased Al content is expected), as well as a number of control samples. Trace elements were analyzed to study possible compositional differences other than the Al content. The analyses were done using large volume HPGe detectors; because of the low abundances, accuracy and precision vary between 3–80% for individual elements. We found a difference between the rare earth element (REE) patterns for apatite and oxalate kidney stones, and a fractionation compared to typical REE contents in plants. For the brain samples there is evidence for differences between the dialysis patient and the control samples not only for Al, but also for some other elements including the REEs, but most differences are minimal, and may not be significant.     

Radioactivity of Phosphate Ores from Karatas-Mazidag Phosphate Deposit of Turkey

The specific activities of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K in the composite samples of phosphate ores of type 1 (grey-coloured ore, with high P₂O₅ (21–35%) and low calcite content) and of type II (grey coloured calcite ore, with low P₂O₅ content (5–17%)) of Karatas-Mazidag phosphate deposit, Turkey, have been determined by gamma spectrometry together with phosphatic animal feed ingredients. The concentrations of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K were found to be up to 557, 625, 26 and 297 Bq·kg^–1, respectively. Radium equivalent activities of samples examined were calculated and compared with those given in the literature. Uranium concentration of the individual phosphate samples, from which composite samples of ores of type I and II have been prepared, were found to show an increasing trend with increasing P₂O₅ and F concentrations.     

Concentration levels of rare-earth elements and thorium in plants from the Morro do Ferro environment as an indicator for the biological availability of transuranium elements

Plants and soils from a natural thorium and rare-earth element occurrence (Morro do Ferro, Brazil) were analyzed by alpha spectrometry (Th) and ICP-AES (REE), after pre-concentration of the elements by solvent extraction, co-precipitation and ion exchange procedures. Leaching experiments with humic acid solutions and different soils were performed to estimate the fraction of elements biologically available. High concentrations of the light rare-earth elements (LREE) and of Th, reaching some hundreds of g/g-ash, were measured in plant leaves from the areas of the highest concentration of these elements in soil and in near-surface waters. Chondrite normalized REE plots of plant leaves and corresponding soils are very similar, suggesting that there is no significant fractionation between the REE during uptake from the soil solution and incorporation into the leaves. However, Ce-depletion was observed for some plant species, increasing forSolanum ciliatum in the sequence: leaves<fruits<seeds. Soil to plant concentration ratios (CR's) for Th and the REE, based on the total concentration of these elements in soils, are in the range of 10^–3 to 10^–2. Leaching experiments confirmed the importance of humic acid complexation for the bio-uptake of Th and REE and further showed that only a very small fraction of these elements in soil is leachable. The implications of these results on the calculated CR's will be discussed.     

Determination of rare earth elements in Indian kimberlite using inductively coupled plasma mass spectrometer (ICP-MS)

A method has been developed for the analysis of rare earth elements (REEs) in kimberlite samples using inductively coupled plasma mass spectrometer (ICP-MS). The samples were dissolved using sodium peroxide fusion and after appropriate dilutions the solutions were analyzed using ICP-MS. The paper presents the concentration of rare-earth elements as determined by ICP-MS in eight kimberlite samples from Central India. The method was validated using certified reference materials STSD-1 and STSD-2 from Canadian Certified Reference Material Project. The method detection limit of various REEs varies from 0.12 to 1.54?mg?kg^?1. The total REE concentrations range from 418 to 726?mg?kg^?1 and fall within the interval of those reported in the literature for kimberlites. Despite the marked difference in the REE contents, all the analyzed samples show similar REE patterns that resemble those for kimberlites. In order to compare ICP-MS results, the samples were analyzed using instrumental neutron activation analysis which is a reference method for determination of REEs in geological samples.     

Determination of rare earth elements in tomato plants by inductively coupled plasma mass spectrometry techniques

In recent years identification of the geographical origin of food has grown more important as consumers have become interested in knowing the provenance of the food that they purchase and eat. Certification schemes and labels have thus been developed to protect consumers and genuine producers from the improper use of popular brand names or renowned geographical origins. As the tomato is one of the major components of what is considered to be the healthy Mediterranean diet, it is important to be able to determine the geographical origin of tomatoes and tomato‐based products such as tomato sauce. The aim of this work is to develop an analytical method to determine rare earth elements (RRE) for the control of the geographic origin of tomatoes. The content of REE in tomato plant samples collected from an agricultural area in Piacenza, Italy, was determined, using four different digestion procedures with and without HF. Microwave dissolution with HNO₃ + H₂O₂ proved to be the most suitable digestion procedure. Inductively coupled plasma quadrupole mass spectrometry (ICPQMS) and inductively coupled plasma sector field plasma mass spectrometry (ICPSFMS) instruments, both coupled with a desolvation system, were used to determine the REE in tomato plants in two different laboratories. A matched calibration curve method was used for the quantification of the analytes. The detection limits (MDLs) of the method ranged from 0.03 ng g^?1 for Ho, Tm, and Lu to 2 ng g^?1 for La and Ce. The precision, in terms of relative standard deviation on six replicates, was good, with values ranging, on average, from 6.0% for LREE (light rare earth elements) to 16.5% for HREE (heavy rare earth elements). These detection limits allowed the determination of the very low concentrations of REE present in tomato berries. For the concentrations of REE in tomato plants, the following trend was observed: roots > leaves > stems > berries. Copyright © 2009 John Wiley & Sons, Ltd.     

An improved method for99Tc analysis and application to human tissues

Zircon separated from samples of monazite in beach sand have been analyzed for Zr, Hf, U, Th, Sc and REE concentration by the neutron activation analysis technique. After irradiation, the rare earth elements were separated from Zr and Hf by oxalate precipitation, using La as a carrier, from²³⁹Np/U/ by ion-exchange chromatographic method and from²³³Pa/Th/ by co-precipitation with MnO₂. The chondritic normalized REE pattern of two zircon samples show negative Eu anomalies with a slope increasing at the heavy rare earths.     

Rare earth element (REE) in surface mangrove sediment by instrumental neutron activation analysis

A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 10¹² cm^?2 s^?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75).     

Fine-powder Al2O3 and SiO2 for preparation of multielement standards for rare-earth element analysis

The present paper based on experimental results contains discussions and suggestions on the possible use of fine-powder Al₂O₃ and SiO₂ with their original content of microimpurities of up to 40 elements, as multielement standards for neutron activation analysis. For example, activation analysis of As, Au, Ba, Cr, Cs, Fe, Ga, K, Ni, Sb, Sc, Se, Sr, Ta, Th, Ti, U, W, Zn, Zr and the REE La, Ce, Nd, Sm, Eu, Tb, Tm, Yb contained in SiO₂ powder off MERCK reagents showed their concentrations to be 0.1 to 5% of those in IAEA standard SL-1. In Al₂O₃ this level is even lower, approximately 10 times and more for the majority of the above-mentioned elements. As Al₂O₃ and SiO₂ are good sorbents for the majority of elements, additional introduction of some elements may allow more methods of analysis. The homogeneity of Al₂O₃ and SiO₂ samples both in the original state and after introduction of some elements was determined by neutron activation analysis, and the SD did not exceed 1% for an Al₂O₃ sample weight of 0.1 g, and 2% for SiO₂.     

Determination of Rare Earth Elements in Acid Mine Drainage by Inductively Coupled Plasma Mass Spectrometry

A method was developed for the direct determination of 14 naturally occuring rare earth elements (REE, La–Lu) by means of inductively coupled plasma mass spectrometry in seepage waters caused by acid mine drainage. The analytical procedure includes the additional determination of oxide and hydroxide formation by Ba and REE. The determined polyatomic ion formation can be used to correct spectral interferences of oxides and hydroxides of Ba and the light REE on middle and heavy REE. The total REE content in the acidic seepage waters investigated is up to 220µgL^–1. The concentration of the REE normalized to Post Archean Australian Shale (PAAS) is shown, and fractionation of the REE is discussed. The PAAS-normalized REE-patterns feature an enrichment of middle and heavy REE as opposed to the light ones. For one seepage water sampled over a period of about half a year, the REE patterns show very high reproducibility. The accuracy of the method was demonstrated by the analysis of two water samples containing certified concentrations of REE.     

Rare earth elements determination and distribution patterns in sediments of a polluted marine environment by instrumental neutron activation analysis

Results obtained from the analysis of sediment core samples taken froma fairly polluted marine environment were analyzed for the REE contents todetermine the concentrations of La, Ce, Sm, Eu, Tb, Dy and Yb using instrumentalneutron activation analysis. Core samples were divided into strata of between2 to 3 cm intervals and prepared in the powdered form before irradiating themin a neutron flux of about 5.0 . 10¹² n . cm ^—2s ^—1 in a Triga Mark II reactor. Down-core concentration profilesof La, Ce, Sm, Eu, Tb, Dy and Yb in 3 core sediments from three sites areobtained. The shale-normalized REE pattern from each site was examined andlater used to explain the history of sedimentation by natural processes suchas shoreline erosion and weathering products deposited on the seabed and furnishingsome baseline data and/or pollution trend occurring within the study area.The shale-normalized REE patterns also showed that LREE in the sediment samplesexhibit enrichment relative to HREE particularly, La and Sm showing enrichmentcompared to the ratios in shale. REE concentrations of 124 µg/g at thesurface of sediment collected at two of the three sites were found to decreaseto 58 and 95 µg/g, respectively. This was of particular interest whenit is used to explain the anomalies occurring in the marine sediment as aresult of geochemical processes over a long period of time. Changes in concentrationsfrom surface to bottom of the sediments ratioed to Sm concentrations and thecorrelation between concentrations of Sm and these elements were also investigatedand correlation coefficients were calculated for all REEs and sites. Validationof the method used was done using a Soil-7 SRM.     

Inductively coupled plasma atomic emission spectroscopic determination of rare earth elements in geological samples after preconcentration by countercurrent chromatography—Part II

This paper directly links up with Part I [Spectrochim. Acta 48B, 1365 (1993)] which treats the first application of countercurrent chromatography (CCC) for pre-separation of rare earth elements (REE) in rocks. The rapid and reliable separation and pre-concentration of “light” REE and Y can be achieved using a system of 0.5 mol/l di-2-ethylhexylphosphoric acid (D2EHPA) in n-decane-hydrochloric acid of different concentrations and a planetary centrifuge as a CCC device. However, Tm, Yb and Lu are partially retained in the stationary phase. Comparative data is presented on three other two-phase liquid systems containing trioctylphosphine oxide (TOPO); D2EHPA and TOPO mixtures and diphenyl(dibutylcarbamoylmethylphosphine)oxide (Ph₂-Bu₂) as extractants in terms of their ability for whole REE group complete isolation from the rock constituents. The partial losses of “light” REE (La and Ce) occurred in the system of 0.1 mol/l solution of TOPO in isobutylmethylketone (IBMK) (stationary phase)-1 mol/l NH₄NO₃-6 mol/l HCl aqueous solutions (mobile phase). Complete isolution of the entire REE group can be reached in two systems: 0.3 mol/l D2EHPA + 0.02 ml/l TOPO in the solvents mixture (3:1) of n-decane + IBMK, respectively (stationary phase)-1 mol/l NH₄NO₃-6 mol/l HCl aqueous solution (mobile phase), and 1.0 mol/l Ph₂-Bu₂ solution in chloroform (stationary phase)-3 mol/l HNO₃ aqueous solution (mobile phase). The D2EHPA + TOPO mixture is recommended as more economic and accessible.     

Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils

With the continual increase in the utilisation of rare earth elements (REE) for industrial and agricultural purposes, research into the environmental and biogeochemical behaviour of REE had attracted much interest in recent times. This study principally describes the distribution of REE in four different types of soils like lateritic soil (S-1), in situ natural soil (S-2), soil contaminated by mining activity (S-3) and accidentally polluted soil (S-4) utilizing the optimised BCR sequential extraction procedure and partial extractions with various types of single extractants such as unbuffered salt solutions 0.1 M NaNO₃, 0.01 M CaCl₂, 1 M NH₄NO₃; complexing agents 0.005 M DTPA and 0.05 M EDTA; acid solutions 0.43 M CH₃COOH and 1 M HCl. Comparison of the sum of the four BCR fractions, which included an aqua regia attack on the residue, with the pseudo-total aqua regia digest values to assess the accuracy of the BCR partioning approach has been undertaken. Partial extraction results with several single extractants have also been reported for all the REE elements including yttrium which have been analysed by the optimised BCR procedure. Results obtained after 24 h extraction with each of the single extractant have also been discussed. The extraction with 1 M HCl during 24 h yielded similar quantities of REE as those released under the combined steps of 1, 2 and 3 of the BCR sequential extraction for all the four different type of soil samples indicating that this reagent can be used successfully to estimate the total extractable contents of REE in various types of soil samples.     

Determination of the REE and Y in silicate materials with ICP-AES

Summary An ICP-AES method for the determination of 12 rare earth elements and Y is described. Following a Na₂O₂-sinter dissolution of silicate materials the REE and Y were separated and concentrated using ion-exchange chromatography. The dissolution and separation procedures are described in detail. Numerous tests show good recovery of the REE. Spectral interferences were quantified and discussed. The precision is better than 5% (r.s.d.) for all measured REE, except Pr. The accuracy was tested by analyzing more than 30 international reference samples, the results are in good agreement with published data. In this paper we present our latest data from 6 new reference samples.

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Bestimmung der Seltenen Erden und Yttrium in silikatischem Material mit ICP-AES

     

Determination of gadolinium in river water by SPE preconcentration and ICP-MS

An analytical scheme was developed for the determination of Gd-diethylenetriaminepentaacetate (Gd-DTPA), Gd and the other rare earth elements (REE) in river water by inductively coupled plasma (quadrupole) mass spectrometry (ICP-Q-MS). The preconcentration step was essential, since the limits of detection of this multielemental analytical technique are higher than the trace concentrations of the interesting elements in river water.Solid phase extraction (SPE) with different commercially available complexing agents (Chelex 100, Toyopearl and ethylhexylphosphates) was employed for the preconcentration of REE. The investigations revealed that complex stability (varying in dependence of the pH value) has a strong influence on the degree of the enrichment of Gd-DTPA. Based on acidified water samples (pH<3) a procedure using ethylhexylphosphates was proposed for the preconcentration of Gd and REE from surface water samples. For this purpose C₁₈-cartridges loaded with ethylhexylphosphates were used, resulting in an enrichment factor of 40.     

The non-destructive determination of REE in fossilized bone using synchrotron radiation induced K-line X-ray microfluorescence analysis

The sensitivity and applicability of the synchrotron radiation induced X-ray microfluorescence (μ-SRXRF) spectrometer at the Hamburg synchrotron laboratory Hasylab for the determination of the distribution of trace concentrations of rare-earth elements (REE) in fossilized bone are discussed and critically compared to those of other trace analytical methods such as instrumental neutron activation analysis (INAA) and LAMP-ICPMS (laser ablation microprobe inductively-coupled plasma mass spectrometry). Measurements were carried out on two bone samples from contrasting terrestrial depositional environments at Olduvai Gorge (Tanzania). Results indicate that the microdistribution of the REE in these biological materials is not homogeneous and that the relative abundance of these elements can provide information on the palaeoenvironment during the fossilization process. The heterogeneous distribution of the REE can be determined in a quantitative and completely non-destructive manner provided the concentrations of individual REE are above 10 μg/g. Received: 18 January 1998 / Revised: 6 October 1998 / Accepted: 10 October 1998     

Rare Earth Elements and Bioavailability in Northern and Southern Central Red Sea Mangroves,Saudi Arabia

Different hypotheses have been tested about the fractionation and bioavailability of rare earth elements (REE) in mangrove ecosystems. Rare earth elements and bioavailability in the mangrove ecosystem have been of significant concern and are recognized globally as emerging pollutants. Bioavailability and fractionation of rare earth elements were assessed in Jazan and AlWajah mangrove ecosystems. Comparisons between rare earth elements, multi-elemental ratios, geo-accumulation index (Igeo), and bio-concentration factor (BCF) for the two mangroves and the influence of sediment grain size types on concentrations of rare earth elements were carried out. A substantial difference in mean concentrations (mg/kg) of REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) was established, except for mean concentrations of Eu, Gd, Tb, Tm, and Lu. In addition, concentrations of REEs were higher in the Jazan mangrove ecosystem. However, REE composition in the two mangroves was dominated by the lighter REE (LREE and MREE), and formed the major contribution to the total sum of REE at 10.2–78.4%, which was greater than the HREE contribution of 11.3–12.9%. The Post Archean Australian Shale (PAAS) normalized values revealed that lighter REE (LREE and MREE) were steadily enriched above heavy REE. More so, low and negative values of R_(H/M) were recorded in the Al Wajah mangrove, indicating higher HREE depletion there. The values of BCF for REEs were less than 1 for all the REEs determined; the recorded BCF for Lu (0.33) and Tm (0.32) were the highest, while the lowest BCF recorded was for Nd (0.09). There is a need for periodic monitoring of REE concentrations in the mangroves to keep track of the sources of this metal contamination and develop conservation and control strategies for these important ecosystems.     

Determination of mercury in polluted soils surrounding a chlor-alkali plant: Direct speciation by X-ray absorption spectroscopy techniques and preliminary geochemical characterisation of the area

Soil samples collected in the surroundings of a chlor-alkali plant in the Netherlands were characterised by synchrotron-based techniques and conventional analytical procedures, in order to evaluate the environmental impact of Hg emissions and other heavy metals present in these locations. Analysis of total metal content by inductively coupled plasma-optical spectroscopy (ICP-OES) revealed a heterogeneous contamination of Hg, with concentrations ranging from 4.3 to 1150 μg g⁻¹. In addition, significant concentrations of Cu, Ni, Pb, Zn, Mn and principally Fe were also identified within the studied samples. Direct determination of mercury species by X-ray absorption near edge spectroscopy (XANES) showed inorganic Hg compounds to prevail in all soils, being Cinnabar (HgS_red) and Corderoite (Hg₃S₂Cl₂) the main species. Nevertheless, more soluble mercury compounds, such as HgO and HgSO₄, have been also identified in significant proportion (from 6 to 20% of total mercury content), indicating a potential risk of mercury mobilisation. On the other hand, the application of sequential extraction schemes (SES) revealed large portions of weakly available Hg extracted in the residual fraction, while Hg associated to the exchangeable phase amounts as much as 19% of total Hg, thus, supporting the results obtained by XANES.Finally, synchrotron-based micro X-ray fluorescence (μ-XRF) was applied to identify qualitative trends on elemental associations in sample particles through a systematic mapping of its surface. In this concern, results show a well-defined correlation between Hg and Cu/Ni in the analysed particles. On the other hand, an absence of correlation between Hg and several other elements (Fe, Ti, Ca, Zn, Mn and S) was also observed. These effects have been attributed to chemical and physical interactions of mercury species on both enriched particles and sample matrices.     

Application of bromine trifluoride for pre-concentration and determination of rare-earth elements in fuel uranium dioxide

Radioactive indicator's (¹⁵²Eu) method was used to study the behavior of rare-earth element (REE) micro-impurities at fluorination of fuel UO₂ with bromine trifluoride. The proposed process is very simple and carried out under a blanket layer of Freon-113 in the glassy carbon (vitreous) crucibles.It was shown that uranium matrix completely removes from reaction sphere in the form of UF₆ and REE contaminations quantitatively remain in crucible owing to practical non-volatility of their fluorides. High purity of fuel UO₂ causes small amount of the non-volatile rest (0.3-2 wt.% from initial weight) that considerably facilitates a problem of confident diagnostics of the strictly limited REE content in this material. Removal of uranium and concentration of REE from analyzed test samples via fluorination is several hundred times more rapid scheme of pre-sampling to atomic emission spectral determination of REE micro-quantities in UO₂ than traditionally used extraction and ion-exchange ways of the preliminary concentration of contaminations and removal of uranium.