Determination of REEs in seawater by ICP-MS after on-line preconcentration using a syringe-driven chelating column

Development of a fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater

Rare earth elements (REEs) are useful geological indicators of marine geochemistry. However, extremely low concentrations (sub-ng L⁻¹) and high-salt matrices result in inefficient measurements. A fully automatic separation system (ELSPE-2 Precon) is used in the online determination of ultra-trace REEs in seawater using inductively coupled plasma mass spectrometry. This system mainly comprises three sections: (i) an auto-sampler (eas-2A) with 120 positions; (ii) a poly(styrene-divinylbenzene) resin column (Prin-Cen Col007) with iminodiacetic and ethylenediaminetriacetic acid functional groups to eliminate the high-salt matrix (e.g., Na, Ca, K, Mg, Al, Ba, Fe, Sr, P, and S) and preserve the target REEs; and (iii) a Trp002 cleanup column for the reduction of the reagent and procedural blank values. The detection limits (3σ) were in the range 0.002 (Dy)–0.097 ng L⁻¹ (La), and the long-term reproducibility (8 h) was between 80% and 120% for all REEs in a 3.5% NaCl matrix solution. The accuracy of this method was verified using a seawater reference material (NASS-6), and the measured REE concentrations were consistent with those previously reported. The proposed online system was used to investigate coastal water samples with varying salinities from the Pearl River Estuary (Guangdong, China). Variations in the REE distribution patterns of different layers of seawater were observed, which could be due to the mixing of potentially light rare earth element-enriched bottom seawater. Moreover, a positive Gd anomaly in river water and seawater might be attributed to anthropogenic pollution from hospitals and the pharmaceutical industry.

A new fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater.

How Feasible is Direct Determination of Rare Earth Elements in Seawater by ICP-MS?

With the increasingly wide industrial use of rare earth elements (REEs), their release into marine systems makes it important to understand in what quantities they occur and to what geochemical processes they contribute, preferably using direct analytical methodology. In this study, analytical performance of high-resolution ICP-MS was assessed with regard to quantification of REEs in seawater without matrix separation and analyte preconcentration. With optimized sample dilution, precise and interference-free quantifications of most of the REEs in samples taken from Kara Sea were obtained, with an accuracy of 3 to 9% (against the independently asserted values), repeatability of 3 to 5%, and intermediate precision and reproducibility, averaging 4 and 11%, respectively. The method was further validated by using a certified reference material for nearshore seawater. However, the limits of detection obtained (0.04 - 0.38 ng L^-1), while not significantly inferior to those obtained after sample enrichment, appear to be not low enough to analyze high salinity sea samples (over 30 parts per thousand) or open-ocean water samples, which require higher dilution factors or contain (much) lower REE concentrations, respectively. Therefore, it was concluded that the direct determination of REEs is only possible from samples with moderate salinity such as estuarine or shallow-sea water. In the latter case, the longitudinal REE profiling assayed by ICP-MS allowed us to assume that the export of the contaminated material from land areas into estuaries and then to the sea by rivers may substantially contribute to the seawater pool of REEs.

Determination of Rare Earth Elements in Pore Water Samples of Marine Sediments Using an Offline Preconcentration Method

The concentrations of dissolved yttrium and rare earth elements (REY) in sediment pore water provide important geochemical information. However, due to the low REY concentration, complex matrix, and limited sample volume (often only a few milliliters), analysis of the REY in pore water often is highly challenging. In this study, a method was established to determine the dissolved REY in pore water of marine sediments using an offline preconcentration step with the ethylenediaminetriacetate chelating resin, followed by inductively coupled plasma-mass spectrometry. In addition, using a commercially available automated trace-element preconcentration system, the preconcentration step can be fully automated, saving labor and providing a better control of the final elution volume. The experimental conditions (pH, elution volume, elution acid concentration, and organic complexation effect) were assessed, and the optimal conditions were chosen. In particular, the organic complexation effect was found to be negligible. The procedure blank and limit of detection were satisfactory for studying REY in pore water of marine sediments, and the method also yielded satisfactory recoveries for the REY elements (83-110%). The method was then applied to analyze the dissolved REY concentrations of pore water samples collected in a sediment core (~ 30 cm) in the central Indian Ocean. The vertical distribution, dissolved REY concentration, and the average Post Archean Australian Shale-normalized pattern of the REY showed similarities to the previously published pore water REY data. This method provides an accurate yet facile approach for the analysis of all 15 REY in marine pore water samples using the sample volume of only ~ 5 mL.

Rapid Identification of Geographical Origin of Commercial Soybean Marketed in Vietnam by ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) analytical method was used to determine the content of 40 elements in 38 soybean samples (Glycine Max) from 4 countries. Multivariate statistical methods, such as principal components analysis (PCA), were performed to analyze the obtained data to establish the provenance of the soybeans. Although soybean is widely marketed in many countries, no universal method is used to discriminate the origin of these cereals. Our study introduced the initial step to the identification of the geographical origin of commercial soybean marketed in Vietnam. The analysis pointed out that there are significant differences in the mean of 33 of the 40 analyzed elements among 4 countries' soybean samples, namely, ¹¹B, ²⁷Al, ⁴⁴Ca, ⁴⁵Sc, ⁴⁷Ti, ⁵⁵Mn, ⁵⁶Fe, ⁵⁹Co, ⁶⁰Ni, ⁶³Cu, ⁶⁶Zn, ⁶⁹Ga, ⁷⁵As, ⁷⁸Se, ⁸⁵Rb, ⁸⁸Sr, ⁸⁹Y, ⁹⁰Zr, ⁹³Nb, ⁹⁵Mo, ¹⁰³Rh, ¹³⁷Ba, ¹⁶³Dy, ¹⁶⁵Ho, ¹⁷⁵Lu, ¹⁷⁸Hf, ¹⁸¹Ta, ¹⁸²W, ¹⁸⁵Re, ¹⁹⁷Au, ²⁰²Hg, ²⁰⁵Tl, and ²⁰⁸Pb. The PCA analysis showed that the soybean samples can be classified correctly according to their original locations. This research can be used as a prerequisite for future studies of using the combination of elemental composition analysis with statistical classification methods for an accurate provenance establishment of soybean, which determined a variation of key markers for the original discrimination of soybean.

Determination of rare earth elements concentrations in natural waters - A review of ICP-MS measurement approaches

Since the rare earth elements (REEs) determination in waters is still not a routine procedure, different analytical protocols have been developed to deal with complexity and variability of sample matrices, problems caused by spectral and non-spectral interferences, insufficient instruments sensitivity, potential contamination and lack of certified reference materials. The aim of this work is to review the current measurement approaches given for REEs total concentrations in natural water samples, including surface and groundwaters as well as rain water and Antarctic ice. As inductively coupled plasma mass spectrometry (ICP-MS) has become the most widely employed technique for analysis of trace concentrations of REEs in aqueous samples it has been intended to present the common issues affecting the measurement results. Apart from a sample preparation step, various configurations of mass spectrometers and sample introduction systems, means of interferences elimination or correction, and calibration strategies used in analytical approaches for REEs analysis are discussed and compared.

Fast Determination of Yttrium and Rare Earth Elements in Seawater by Inductively Coupled Plasma-Mass Spectrometry after Online Flow Injection Pretreatment

A method for daily monitoring of yttrium and rare earth elements (YREEs) in seawater using a cheap flow injection system online coupled to inductively coupled plasma-mass spectrometry is reported. Toyopearl AF Chelate 650M^® resin permits separation and concentration of YREEs using a simple external calibration. A running cycle consumed 6 mL sample and took 5.3 min, providing a throughput of 11 samples per hour. Linear ranges were up to 200 ng kg⁻¹ except Tm (100 ng kg⁻¹). The precision of the method was <6% (RSDs, n = 5), and recoveries ranged from 93% to 106%. Limits of detection (LODs) were in the range 0.002 ng kg⁻¹ (Tm) to 0.078 ng kg⁻¹ (Ce). Good agreement between YREEs concentrations in CASS-4 and SLEW-3 obtained in this work and results from other studies was observed. The proposed method was applied to the determination of YREEs in seawater from the Jiulong River Estuary and the Taiwan Strait.

Separation/Preconcentration Techniques for Rare Earth Elements Analysis

The main aim of this chapter exactly characterizes the contribution. The analytical chemistry of the rare earth elements (REEs) very often is highly complicated and the determination of a specific element is impossible without a sample pre-concentration. Sample preparation can be carried out either by separation of the REEs from the matrix or by concentrating the REEs. The separation of REEs from each other is mainly made by chromatography.

At the beginning of REE analysis, the method of precipitation/coprecipitation was applied for the treatment of REE mixtures. The method is not applicable for the separation of trace amounts of REEs. The majority of the methods used are based on the distribution of REEs in a two-phase system, a liquid–liquid or a liquid–solid system. Various techniques have been developed for the liquid–liquid extraction (LLE), in particular the liquid phase micro-extraction. The extraction is always combined with a pre-concentration of the REEs in a single drop of extractant or in a hollow fiber filled with the extractant. Further modified techniques for special applications and for difficult REE separation have been developed. Compared to the LLE, the solid phase micro-extraction is preferred. The method is robust and easy to handle, in which the solid phase loaded with the REEs can be used directly for subsequent determination methods. At present, very new solid materials, like nanotubes, are developed and tested for solid phase extraction.

Statistical Analysis of Mineral Concentration for the Geographic Identification of Garlic Samples from Sicily (Italy), Tunisia and Spain

We performed a statistical analysis of the concentration of mineral elements, by means of inductively coupled plasma mass spectrometry (ICP-MS), in different varieties of garlic from Spain, Tunisia, and Italy. Nubia Red Garlic (Sicily) is one of the most known Italian varieties that belongs to traditional Italian food products (P.A.T.) of the Ministry of Agriculture, Food, and Forestry. The obtained results suggest that the concentrations of the considered elements may serve as geographical indicators for the discrimination of the origin of the different samples. In particular, we found a relatively high content of Selenium in the garlic variety known as Nubia red garlic, and, indeed, it could be used as an anticarcinogenic agent.

Determination of Rare Earth Elements in Hypersaline Solutions Using Low-Volume, Liquid-Liquid Extraction

Complex, hypersaline brines-including those coproduced with oil and gas, rejected from desalination technologies, or used as working fluids for geothermal electricity generation-could contain critical materials such as the rare earth elements (REE) in valuable concentrations. Accurate quantitation of these analytes in complex, aqueous matrices is necessary for evaluation and implementation of systems aimed at recovering those critical materials. However, most analytical methods for measuring trace metals have not been validated for highly saline and/or chemically complex brines. Here we modified and optimized previously published liquid-liquid extraction (LLE) techniques using bis(2-ethylhexyl) phosphate as the extractant in a heptane diluent, and studied its efficacy for REE recovery as a function of three primary variables: background salinity (as NaCl), concentration of a competing species (here Fe), and concentration of dissolved organic carbon (DOC). Results showed that the modified LLE was robust to a range of salinity, Fe, and DOC concentrations studied as well as constant, elevated Ba concentrations. With proper characterization of the natural samples of interest, this method could be deployed for accurate analysis of REE in small volumes of hyper-saline and chemically complex brines.

Synthesis and characterization of lysine-modified SBA-15 and its selective adsorption of scandium from a solution of rare earth elements

A novel lysine-functionalized mesoporous material was synthesized using a facile two-step post-grafting method, selectively adsorbing scandium from aqueous solution.

A magnesium hydroxide preconcentration/matrix reduction method for the analysis of rare earth elements in water samples using laser ablation inductively coupled plasma mass spectrometry

This paper describes a simple method for simultaneous preconcentration and matrix reduction during the analysis of rare earth elements (REEs) in water samples through laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). From a systematic investigation of the co-precipitation of REEs using magnesium hydroxide, we optimized the effects of several parameters - the pH, the amount of magnesium, the shaking time, the efficiency of Ba removal, and the sample matrix - to ensure quantitative recoveries. We employed repetitive laser ablation to remove the dried-droplet samples from the filter medium and introduce them into the ICP-MS system for determinations of REEs. The enrichment factors ranged from 8 to 88. The detection limit, at an enrichment factor of 32, ranged from 0.03 to 0.20 pg mL(-1). The relative standard deviations for the determination of REEs at a concentration of 1 ng mL(-1) when processing 40 mL sample solution were 2.0-4.8%. We applied this method to the satisfactory determination of REEs in lake water and synthetic seawater samples.