Flow injection on-line solid phase extraction coupled with inductively coupled plasma mass spectrometry for determination of (Ultra)trace rare earth elements in environmental materials using maleic acid grafted polytetrafluoroethylene fibers as sorbent

A new sorbent, maleic acid grafted polytetrafluoroethylene fiber (MA-PTFE), was prepared and evaluated for on-line solid-phase extraction coupled with inductively coupled plasma mass spectrometry (ICP-MS) for fast, selective, and sensitive determination of (ultra)trace rare earth elements (REEs) in environmental samples. The REEs in aqueous samples at pH = 3.0 were selectively extracted onto a microcolumn packed with the MA-PTFE fiber, and the adsorbed REEs were subsequently eluted on-line with 0.9 mol l(-1) HNO3 for ICP-MS determination. The new sorbent extraction system allows effective preconcentration and separation of the REEs from the major matrix constituents of alkali and alkali earth elements, particularly their separation from barium that produces considerable isobaric interferences of 134Ba16O1H+, 135Ba16O+, 136Ba16O1H+, and 137Ba16O+ on 151Eu+ and 153Eu+. With the use of a sample loading flow rate of 7.4 ml min(-1) for 120 s preconcentration, enhancement factors of 69-97 and detection limits (3s) of 1-20 pg l(-1) were achieved at a sample throughput of 22 samples h(-1). The precision (RSD) for 16 replicate determinations of 50 ng l(-1) of REEs was 0.5-1.1%. The developed method was successfully applied to the determination of (ultra)trace REEs in sediment, soil, and seawater samples.     

Novel Sorbent Extraction Technique Using a Chelating Agent Impregnated Porous PTFE Filter Tube: Preconcentration of Rare Earth Elements (REEs) with Bis(2‐Ethyl‐Hexyl)Hydrogen Phosphate (HDEHP) Loaded Porous PTFE Filter Tube Prior to Determination by ICP‐MS

Abstract

Sorbent extraction and elution of rare earth elements (REEs) by using bis(2‐ethyl‐hexyl)hydrogen phosphate (HDEHP) impregnated porous PTFE filter tube were studied. A 100 ng amount of each REEs was quantitatively extracted by filtering 1000 mL of matrix‐free solution under pH 2.0–3.2. For a synthetic seawater sample, extractability of lighter REEs (La–Sm) was lowered; optimum pH range to simultaneously extract all REEs was shifted to 2.9–3.2, and limit of sample volume for quantitative extraction was decreased to 100 mL for La–Sm [although heavier REEs (Eu–Lu) were quantitatively extracted from 1000 mL]. Extracted REEs were quantitatively eluted by filtering through 5 mL of 10 mol/L^?1 hydrochloric acid to the tube. Hence, maximum preconcentration factors were of 200‐ and 20‐fold for Nd–Lu and La–Sm, respectively. Total recovery of 0.5–10 ng of REEs spiked to 300 mL of natural sea salt solution was tested; quantitative recovery (95.9% for Gd–102% for Eu) were obtained for all REEs except La (54.9%). The REEs in the natural sea salt solution were also determined by ICP‐MS after preconcentration with the present method [RSD=16% (La)–1.1% (Yb), n=3].     

Determination of rare earth elements in seawater by on-line column preconcentration inductively coupled plasma mass spectrometry

A home made column of commercially available iminodiacetate resin, Muromac A-1 (50–100 mesh) was used to concentrate rare earth elements (REEs) (15 elements: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in seawater. An automated low pressure flow analysis method with on-line column preconcentration/inductively coupled plasma mass spectrometry (ICP-MS) is described for the determination of REEs in seawater. Sample solutions (adjusted to pH of 3.0) passed through the column. After washing the column with water, the adsorbed elements were subsequently eluted into the plasma with 0.7 M nitric acid. Calibration curves were accomplished by means of purified artificial seawater with a sample loading time of 120 s. Detection limits (DLs) of the on-line column preconcentration/ICP-MS by eight replicate operations were between 0.040 and 0.251 pg ml⁻¹ for REEs in the artificial seawater. The precision was less than 8.9% for REEs and one sample can be processed in 7 min using a 7 ml of sample. The proposed method was applied to determine REEs in coastal seawater of Hiroshima Bay, Japan.     

Determination of rare earth elements in geological samples by inductively-coupled plasma atomic emission spectrometry after oxalate coprecipitation and cation-exchange column separation

A method for separation and determination of traces of 14 rare earth elements (REEs) in geological samples is described. Determination by inductively-coupled plasma atomic emission spectrometry follows oxalate coprecipitation of the REEs with calcium as carrier and cation- exchange column separation in nitric acid. The combination of the two separation techniques improved the low recoveries found for Sm, Eu, and Gd when only ion-exchange was used, especially for iron- and aluminum-rich samples. The method was applied to the analysis of geological standard materials NBS SRM 688 (basalt), NBS SRM 278 (obsidian), GSJ JB-1 (basalt), GSJ JA- 2 (andesite), and CCRMP SY-3 (syenite). The results were evaluated on the basis of chondrite- normalized rare earth element distribution patterns.     

Use of a microcolumn packed with modified carbon nanofibers coupled with inductively coupled plasma mass spectrometry for simultaneous on-line preconcentration and determination of trace rare earth elements in biological samples

In this work, a new method was developed for the determination of trace rare earth elements (REEs) in biological samples by inductively coupled plasma mass spectrometry (ICP-MS) after preconcentration on a microcolumn packed with modified carbon nanofibers (CNFs). CNFs oxidized with nitric acid have been proved to possess an exceptional adsorption capability for REEs due to their surface functionalization. The effects of the experimental parameters, including pH, sample flow rate and volume, elution solution and interfering ions, on the recoveries of the analytes have been investigated systematically. A 100-fold enrichment factor was obtained. The adsorption capacity of CNFs was found to be 18.1, 19.3, 23.6, 17.6, 22.3 and 19.5 mg/g for La, Ce, Sm, Eu, Dy and Y, respectively. Under the optimum conditions, the detection limits of this method ranged from 0.2 pg/mL (Dy) to 1.2 pg/mL (Ce) with an enrichment factor of 15-fold, and the relative standard deviations (RSDs) for the determination of REEs at the 1.0 ng/mL level were less than 4% (n = 9). This method was applied to the analysis of trace REEs in a real sample of human hair with recoveries of 95-115%. In order to validate the proposed method, a certified reference material of human hair (GBW 07601) was analyzed with satisfactory results.     

Preconcentration of rare earth elements on silica gel loaded with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one prior to their determination by ICP-AES.

A new chelating resin, silica gel loaded with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (PMBP), was prepared and used for the preconcentration of trace amounts of rare earth elements (REEs) in water samples prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). REEs (La, Eu, Yb and Y) were quantitatively retained on the column packed with modified silica gel in the pH range 5 - 8 and separated from the matrix, and then recovered by eluting with 2.0 mol L(-1) HNO3. The adsorption capacity of modified silica gel for La, Eu, Yb and Y was 0.208, 0.249, 0.239 and 0.224 mmol g(-1), respectively. The method has been successfully applied for the determination of La, Eu, Yb and Y in geological and environmental samples with satisfactory results.     

REE bound DNA in natural plant

The binding of rare earth elements (REEs) with nucleic acids in the leaves of fern Dicranopteris dichotoma (DD) has been studied by molecular activation analysis (MAA). The REEs bound DNA (REE-DNA) was obtained from the leaves of DD. The CTAB-based procedure was modified for extraction of total DNA. The purity of DNA was examined by UV spectroscopy. The DNA obtained was separated and determined by agarose gel electrophoresis further. Meanwhile, the contents of eight rare earth elements (La, Ce, Nd, Sm, Eu,Tb, Yb and Lu) in REE-DNA were detected by instrumental neutron activation analysis (INAA). The results showed that REE-DNA with higher purity could be extracted from plant using this method. It was also found that REEs were bound firmly with DNA in the leaves of DD. The molecular weight (MW) of REE-DNA band was about 22 kb in agarose gel electrophoresis.     

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.     

Preconcentration of Rare Earth Elements in Seawater with Chelating Resin Having Fluorinated β‐Diketone Immobilized on Styrene Divinyl Benzene for their Determination by ICP‐OES

An analytical method has been developed for the preconcentration of rare earth elements (REEs) in seawater for their determination by inductively coupled plasma optical emission spectrometry (ICP‐OES). An indigenously synthesized chelating resin was used for the preconcentration of (REEs) which was based on immobilization of fluorinated β‐diketone group on solid support styrene divinyl benzene. Sample solutions (adjusted to optimized pH) were passed through a polyethylene column packed with 250 mg of the resin. Experimental conditions consisting of pH, sample flow rate, sample volume and eluent concentration were optimized. The established method has been applied for the preconcentration of light, medium and heavy REEs in coastal sea water samples for their subsequent determination by (ICP‐OES). Percentage recoveries of La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu were ≥ 95%, a preconcentration factor of 200 times, and relative standard deviations < 5% were achieved.     

Measurement of rare earths elements in Kakul phosphorite deposits of Pakistan using instrumental neutron activation analysis

The rare earth elements (REEs) content of Kakul phosphate rock (PR) from different localities of the main Hazara deposits of Pakistan were determined using instrumental neutron activation analysis (INAA). 25 phosphorite samples were collected from different phosphorite sites and 6 samples representing different batches from the crushing plant near Kakul Mine. Concentrations of seven REEs (Ce, Eu, La, Lu, Sm, Tb and Yb) were determined in the PR samples. The highest amounts of Heavy and light rare earth elements (HREE and LREE) were quantified in the PR samples collected at the Phosphate Rock Crushing Plant while the lowest amounts of these REEs were measured in the Lambidogi Phosphorite deposit samples. Comparison with global data showed the REEs content of the studied PRs show lower range for all REEs and mostly comparable to the data reported by Israel and Syria. Calculated chondrite ratio for these elements depicts enrichment of LREEs in all phosphorite deposits.     

Determination of rare earth elements in human blood serum by inductively coupled plasma mass spectrometry after chelating resin preconcentration

The determination of all rare earth elements (REEs) in human blood serum by inductively coupled plasma mass spectrometry (ICP-MS) was performed with the aid of chelating resin (Chelex 100) preconcentration after acid digestion with HNO3 and HClO4. When chelating resin preconcentration was carried out at room temperature, the recoveries of heavy REEs were lower than those of light REEs because of their stable complex formation with residual organic compounds remaining in the digested serum solution. These problems were overcome by heating the solution at 80 degrees C during the chelating resin preconcentration process. As a result, the recoveries for all REEs were improved to 92-102% in the case of a concentration factor of 4, where the analytical detection limits for REEs were below 0.2 x 10(-12) g ml-1. Consequently, all REEs in individual human blood sera collected from five healthy volunteers could be determined by ICP-MS with good precision. The concentrations of REEs in human blood serum were extremely low, in the range from ca. 1 x 10(-12) g ml-1 of Eu to ca. 230 x 10(-12) g ml-1 of Ce.     

Determination of rare earth elements in fern leaves using instrumental neutron activation analysis

The lanthanides (REE) in 142 fern leaves collected from several sampling sites in Japan have been determined by neutron activation analysis, and the correlations between any two REEs in the logarithmic scattering diagram were examined. The relationship was expressed by the general formula, Y=aX+b with a correlation coefficient R. A strong positive correlation was seen between any two REEs in the diagram with a regression coefficient and a correlation coefficient close to unity. However, between Eu or Tb and other REEs the relationship was split into two lines with the same correlation coefficient. From the intercept b, the relative abundance of the two elements was determined for each REE and compared with those in hickory and tobacco leaves. These findings indicated that the abundance pattern of fern leaves is quite different from those of hickory and tobacco leaves. Namely, the relative abundance of La and Ce was quite similar in the three plants, but the abundance of the other REEs (Nd, Sm, Gd, Dy and Lu) was considerably lower in ferns than in hickory and tobacco leaves. For Eu and Tb the higher values obtained in fern leaves coincided with those of the two plants.     

Determination of nitrite with a nano-gold modified glassy carbon electrode by cyclic voltammetry

Abstract

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was employed to determine the concentration of rare earth elements (REEs) in plants and soils. Sample preparation and analytical conditions were investigated to set up a simple routine procedure for measuring rare earth elements. For prompt sample decomposition, a microwave digestion technique was successfully used with an acid mixture of HCl+HNO₃+HF. Detection limits, reproducibility, accuracy and possible interference were also studied. ICP-MS provided extremely low detection limits for REEs (0.6–6ng/l). Precision was typically better than 6% RSD (relative standard deviation) for soil and 10% for plant. The potential of the method was evaluated by analysis of standard reference materials of soils and plants. A good agreement between the experimental results and certified values was observed. The spectroscopic interference of Ba with Eu and light REEs(LREEs, La-Eu) with heavy REEs(HREEs, Gd-Lu) were eliminated by the algebra correction.

The results suggested that REEs in soil samples existed mainly as light REEs, and the same concentration distribution patterns of Oddo-Hakins law were observed, showing negative gradient from La to Lu concentrations. The REE contents in plants were very low, less than 20μg/g and varied with plant species. Apart from rape leaf(Brassica juncea), the REE distribution patterns in other plant leaves were consistent with soils, indicating that these plants generally absorbed REEs from soil without selectivity. Rape leaf showed selective absorption for LREEs, especially for La. The REE concentration distribution in parts of hot pepper(Capsicum annuum) was characteriaed by root>leaf>stem>fruit. The REEs absorbed by hot pepper concentrated mainly in roots and leaves, very little migrated into fruit. Transfer factors(TFs) of REEs in plants were very low. Although the contents of LREEs were relatively more than those of HREEs, no distinct difference of TFs between LREEs and HREEs was observed, meaning that LREEs and HREEs have the same abilities of transportation. However, for rape leaf, the TFs of LREEs were one or two orders of magnitude higher than those of HREEs.     

Determination of valuable elements in natural phosphates

Natural phosphates are used on large scale in the fertilizer industry. The usual process of the chemical attack is sulfuric (predominant) and nitric acids. The liquid phosphoric acid phase resulted contains dissolved valuable elements like: uranium and rare earths elements (REEs). Uranium and REEs are recovered in some technologies as valuable products. It is therefore important to know, uranium and REEs content in natural phosphates in view to decide on their recovery. In this paper determinations were carried out to find the uranium and REEs contents. The concentrations involved are low, therefore, it is difficult to find a classical reliable method without incurring important losses, i. e., errors. In this work uranium and REEs were determined by physical methods like: neutron activation analysis (NAA), emission spectroscopy, mass spark spectrometry and X-ray fluorescence. The results obtained were acceptable and intercomparison between various methods was carried out. It was found that most reliable results were given by mass spark spectrometry and activation analysis. The data resulted are in good agreement with uranium and REEs in the green cake (uranium tetrafluoride) and in the REEs concentrate obtained by solvent, extraction from phosphoric acid.     

ICP-AES determination of trace rare earth elements in environmental and food samples by on-line separation and preconcentration with acetylacetone-modified silica gel using microcolumn.

A novel method of online microcolumn separation and preconcentration coupled to inductively coupled plasma atomic emission spectrometry (ICP-AES) with the use of acetylacetone-modified silica gel as packing material was developed for the determination of trace rare earth elements (REEs) in environmental and food samples. The main parameters affecting online separation/preconcentration, including pH, sample flow rate, sample volume, elution and interfering ions, have been investigated in detail. Under the optimized operating conditions, the adsorption capacity values for Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu were 25.65, 23.23, 24.01, 19.40, 22.89, 23.77, 24.40, 23.96, 25.58, 25.15, 24.86, 22.75, 16.05, 24.13, 26.51 and 27.93 mg g(-1), respectively. Detection limits (3sigma) based on three times standard deviations of the blanks by 8 replicates were in the range from 48 pg mL(-1) for Lu to 1003 pg mL(-1) for Sm. With 90 s preconcentration time and 10 s elution time, the enrichment factor was 10 and the sample frequency was 28 h(-1). The precisions (RSDs) obtained by determination of a 250 ng mL(-1) (n = 8) REEs standard solution were in the range from 1.7% for Y to 4.4% for Sm. The proposed method was successfully applied to the determination of trace REEs in pig liver, agaric and mushroom. To validate the proposed method, we analyzed three certified reference materials (GBW07401 soil, GBW07301a sediment, and GBW07605 tea leaves). The determined values were in a good agreement with the certified values. The method is rapid, selective, sensitive and applicable to the determination of trace REEs in biological and environmental samples with complicated matrix effects.     

ICP-MS Measurement of Trace and Rare Earth Elements in Beach Placer-Deposit Soils of Odisha,East Coast of India,to Estimate Natural Enhancement of Elements in the Environment

Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration of trace and rare earth elements (REEs) in soils. Geochemical certified reference materials such as JLk-1, JB-1, and JB-3 were used for the validation of the analytical method. The measured values were in good agreement with the certified values for all the elements and were within 10% analytical error. Beach placer deposits of soils mainly from Odisha, on the east coast of India, have been selected to study selected trace and rare earth elements (REEs), to estimate enrichment factor (EF) and geoaccumulation index (I_geo) in the natural environment. Enrichment factor (EF) and geoaccumulation index (I_geo) results showed that Cr, Mn, Fe, Co, Zn, Y, Zr, Cd and U were significantly enriched, and Th was extremely enriched. The total content of REEs (ƩREEs) ranged from 101.3 to 12,911.3 µg g⁻¹, with an average 2431.1 µg g⁻¹ which was higher than the average crustal value of ΣREEs. A high concentration of Th and light REEs were strongly correlated, which confirmed soil enrichment with monazite minerals. High ratios of light REEs (LREEs)/heavy REEs (HREEs) with a strong negative Eu anomaly revealed a felsic origin. The comparison of the chondrite normalized REE patterns of soil with hinterland rocks such as granite, charnockite, khondalite and migmatite suggested that enhancement of trace and REEs are of natural origin.     

Detailed study on simultaneous separation of rare earth elements by capillary electrophoresis

Separation of all rare earth elements (REEs) by capillary zone electrophoresis was investigated in a system of alpha-hydroxyisobutyric acid (HIBA) as a main complex reagent and acetic acid (HAc) as an assistant complex reagent. In the combined system, ligand Ac- plays an important role in improving separation of Eu and Gd, and Y and Dy. The calculated ratio of Ac- to HIB- concentrations was compared and demonstrated that Eu and Gd, and Y and Dy tend to be separated at lower, and higher ratio of the two free ligands, respectively. An operational buffer system was developed for a complete separation of all REE ions.     

Rare earths elements in phosphorite and granulated single super-phosphate fertilizers of Pakistan,a study using instrumental neutron activation analysis

Sensitive nondestructive instrumental neutron activation analysis (INAA) technique has been applied for the determination of rare earth elements (REEs) (Ce, Eu, La, Lu, Sm, Tb and Yb) in phosphate rocks (PR) and granulated single super-phosphate (GSSP) fertilizer samples from Hazara district of Pakistan. The comparison of the PR with product fertilizers shows that most of the quantified REEs were found to be in lower contents in the fertilizers. Six fertilizer samples with different N, P and K ratio for distinctive application to plants were also characterized. The REEs in these showed irregular patterns that can be attributed to difference in their manufacturing and chemical processes. The REEs contents of local phosphate fertilizer were found to be lower in comparison to the values cited in the literature; however Ce is relatively high. For quality assurance fair agreement was found between the results obtained for reference materials IAEA SL-1 (Lake Sediment) and GSJ-JR-1 (Rhyolite).     

Improved capillary electrophoresis method for measuring rare-earth elements in synthetic geochemical standards

An improved capillary electrophoresis (CE) method for quantifying rare-earth elements (REEs) in synthetic geochemical standards was developed. Synthetic standard solutions were obtained from high purity metal oxides. The separation of REE total group (lanthanum to lutetium) was defined as a primary objective. Special attention was also focused on the optimized separation of europium (Eu) and gadolinium (Gd) because in earlier applications they presented overlapping problems. Their separation and quantitative determinations are essential for geological applications. For the rapid separation of REEs in synthetic geochemical standards, the temperature of the separation device was optimized. An analysis temperature of 15 degrees C enabled both the rapid separation of REEs within 2 min and the overlapping problem of Eu-Gd to be resolved. The detection limits (<0.1 ng) and precision estimates (generally better than 5%) were found to be satisfactory for most geological applications.     

土壤中稀土元素的形态分析

稀土元素对土壤环境的影响不但与其总量有关,而且与其化学形态关系更为密切。分别采用酸法消解和形态连续提取法对土壤样品中稀土元素总量和稀土元素的形态进行提取分析,并利用电感耦合等离子体质谱法测定了土壤样中稀土元素含量和稀土元素各形态含量。结果表明,采集土壤样品中稀土元素含量为200~1418 mg/kg,轻稀土元素含量远高于重稀土元素;稀土元素各结合形态总和相对于总量的回收率为88.2%~110%,表明采用的连续萃取法适合土壤样品中稀土元素的分析。土壤样品中稀土元素主要以残渣态存在,为33%~80%;晶体铁锰氢氧化物共沉淀态为10%~31%;腐殖质和无定形氧化物吸附态为5.0%~18%;可交换态和碳酸盐结合态为4.0%~23%;无定形铁锰氧化物共沉淀态低于3%。分析了采样点位置和稀土元素性质对稀土元素含量的影响,并讨论了土壤性质对形态分布的影响。