Valence properties of tellurium in different chemical systems and its determination in refractory environmental samples using hydride generation - Atomic fluorescence spectroscopy

Separation and determination of tellurium(IV) and tellurium(VI) using reversed-phase high-performance liquid chromatography-inductively coupled plasma mass spectrometry

A new method for speciation analysis of tellurium(IV) and Te(VI) using high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) has been developed. Tellurium(IV) and Te(VI) were completely separated using a reversed-phase column with an L-cysteine eluent under an isocratic elution condition. The detection limits (3σ) of Te(IV) and Te(VI) monitored by HPLC-ICP-MS at m/z 125 were 1.4 and 0.5 ng g-1, respectively. The proposed determination method was precisely applied to assessing total concentrations and chemical species of Te in several standard solutions. The recovery rates of Te(IV) and Te(VI) were almost 100% from the results of the addition-recovery examinations, even when a high matrix sample such as seawater was measured. The method was applied to seawater samples and electronic products, and was proved quite effective for environmental risk assessment.

Determination of ultra-trace Te species in open ocean waters based on Mg(OH)2 coprecipitation, anion exchange resin column separation and inductively coupled plasma sector-field mass spectrometry using a 125Te-enriched isotope spike

We present a method for the determination of ultra-trace Te species (Te(IV) and Te(VI)) in open ocean waters. The proposed method is based on Mg(OH)2 coprecipitation, anion exchange resin column separation and inductively coupled plasma sector-field mass spectrometry (ICPSFMS) using a 125Te-enriched isotope spike. The largest advantage of the method is that the use of the spike allows accurate and precise determination when it combines with either isotope dilution or recovery correction. Tellurium-IV and VI are preconcentrated in a Mg(OH)2 precipitate and separated mutually by an anion exchange resin column. Te(IV) is retained to the column, while Te(VI) passing through the column is recovered by a subsequent column procedure after reduction of Te(VI) to Te(IV). Te(IV) is successfully eluted with a small amount of 0.01 M HCl. The additional merit of using this eluent is elimination of components that result in a memory effect during the measurement of Te(IV). Possible mass spectral interference on Te(IV) can be excluded by adjusting the mass window, and the Te(IV) concentrations determined by this approach agree well with those independently obtained by an oxidation procedure which removes the interference. The accuracy of the proposed method is verified with homemade standard seawater for which the measured concentrations agree well with results calculated from the value of the standard solution. Procedural blanks for Te(IV) and Te(VI) are 1.5 ± 0.9 pg kg-1 (n = 11) and 1.3 ± 0.9 pg kg-1 (n = 11) with corresponding overall detection limits of 3.0 pg kg-1 and 2.8 pg kg-1, respectively. Using the method, we have clarified vertical profiles of Te(IV) and Te(VI) in the subarctic western North Pacific for the first time.

Non-chromatographic Speciation Analysis of Tellurium by HG-ICP-MS/MS at Sub ng L-1 Concentration in Natural Waters Using TiIII as a Pre-Reducing Agent

An automated and high-throughput (36 h^-1) method for extremely sensitive determination of the two main tellurium species in the environment, namely, tellurite (Te^IV) and tellurate (Te^VI), was developed. Flow injection hydride generation was interfaced for the first time with inductively coupled plasma triple quadrupole mass spectrometry (ICP-MS/MS) detection to assure interference-free tellurium analysis. ICP-MS/MS conditions were studied in detail. Using a mixture of He + O₂ gases in the reaction cell, the background signals significantly dropped and Xe isobaric interference was eliminated, allowing measurement with the most abundant Te isotopes, that is, ¹²⁸Te and ¹³⁰Te, and offering a huge increase in sensitivity. Volatile H₂Te was selectively generated by a HCl/NaBH₄ reaction from Te^IV or from both Te^IV and Te^VI (Te^IV+VI) after pre-reduction of Te^VI by a TiCl₃ solution. The optimum conditions for TiCl₃ as a pre-reductant and the pre-reduction kinetics were also investigated. Different reduction rates were found depending on the sample stabilization media (HCl, HNO₃, or EDTA). The same sensitivity was found for Te^IV and Te^VI, measured after pre-reduction, and no significant matrix effect was observed in both fresh and seawaters. Therefore, external calibration was used for quantification in real samples. Under optimal conditions, this method reached an unprecedented limit of detection of 0.07 ng L^-1 for both Te^IV and Te^IV+VI and an intra-day repeatability of 5.2% at the 5 ng L^-1 level. The methodology was successfully applied to the speciation analyses in commercially available certified reference materials of river water and seawater, and in bottled water and lake water samples.

Accessing the environmental impact of tellurium metal

Tellurium is gaining technical significance because of being a vital constituent for the growth of green-energy products and technologies. Owing to its unique property of interchangeable oxidation states it has a tricky though interesting chemistry with basically unidentified environmental effects. The understanding of environmental actions of tellurium has significant gaps for instance, its existence and effects in various environmental sections related to mining, handling and removal and disposal methods. To bridge this gap it is required to assess its distinctive concentrations in the environment together with proper knowledge of its environmental chemistry. This in turn significantly requires developing systematic diagnostic schemes which are sensitive enough to present statistics in the concentrations which are environmentally relevant. The broad assessment of available statistics illustrates that tellurium is being found in a very scarce concentrations in various environmental sections. Very less information is available for the presence and effects of tellurium in air and natural water resources. Various soil and lake sediment analysis statistics indicate towards the presence of tellurium in soil owing to release of dust, ash and slag during mining and manufacturing practices. Computing the release and behavior of tellurium in environment needs a thorough assessment of its anthropogenic life cycle which in turn will facilitate information about its existing and prospective release in the environment, and will aid to handle the metal more sensibly.

Vanadium Species-Assisted Photochemical Vapor Generation for Direct Detection of Trace Tellurium with Inductively Coupled Plasma Mass Spectrometry

Photochemical vapor generation (PVG) is emerging as an alternative sample introduction method in the field of atomic spectrometry. The addition of transition metals can largely improve the PVG yields of elements with the enhancement of 1.4 to 30 000-fold, based on previous reports. In this work, the use of vanadium species as novel "sensitizers" in PVG was first reported, tellurium (Te) was selected as the target. The efficient photochemical reduction of Te was observed in the presence of 9% (v/v) formic acid (FA), 20%(v/v) acetic acid (AA), and 40 mg L^-1 of V(V) (existing as VO₃^-) with the conversion efficiency of 87 ± 3%. Under the selected conditions, there was no significant difference in analytical sensitivity between Te(IV) and Te(VI), making the direct detection of total Te possible. The limit of detection (LOD, 3σ) was 2.9 ng L^-1 for Te with inductively coupled plasma mass spectrometry (ICP MS) measurement. Good precisions of 2.3% and 2.2% (relative standard deviations, RSD) for seven times replicate measurement of 0.5 μg L^-1 Te(IV) and Te(VI) standard solutions were obtained. The sensitivity was enhanced about 55-fold compared to that using traditional direct solution nebulization. The method was applied for the determination of trace Te in three water samples and two certified reference materials of sediment with satisfactory results. The possible mechanism was investigated. The generation of volatile vanadium along with (CH₃)₂Te was found in PVG for the first time. The new findings in this work will be helpful for exploration of efficient "sensitizers" in PVG and further expanding the scope of elements amenable to PVG as well.

Development of a Tellurium Speciation Study Using IC-ICP-MS on Soil Samples Taken from an Area Associated with the Storage, Processing, and Recovery of Electrowaste

The optimization and validation of a methodology for determining and extracting inorganic ionic Te(VI) and Te(IV) forms in easily-leached fractions of soil by Ion Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS) were studied. In this paper, the total concentration of Te, pH, and red-ox potential were determined. Ions were successfully separated in 4 min on a Hamilton PRPX100 column with 0.002 mg/kg and 0.004 mg/kg limits of detection for Te(VI) and Te(IV), respectively. Soil samples were collected from areas subjected to the influence of an electrowaste processing and sorting plant. Sequential chemical extraction of soils showed that tellurium was bound mainly with sulphides, organic matter, and silicates. Optimization of soil extraction allowed 20% average extraction efficiency to be obtained, using 100 mM citric acid as the extractant. In the tested soil samples, both tellurium species were present. In most cases, the soils contained a reduced Te form, or the concentrations of both species were similar.

Enhanced Photochemical Vapor Generation for the Determination of Bismuth by Inductively Coupled Plasma Mass Spectrometry

An enhanced photochemical vapor generation (PVG) sample introduction procedure is developed for the determination of trace Bi with inductively coupled plasma mass spectrometry (ICP MS) by the addition of iron. Gas chromatography mass spectrometry (GC-MS) reveals that (CH₃)₃Bi is the major component of the volatile Bi species formed in the presence of 20% (v/v) acetic acid, 5% (v/v) formic acid, and 60 μg mL^-1 Fe³⁺ under UV irradiation. The addition of Fe³⁺ not only largely increases the PVG efficiency of Bi³⁺ but also accelerates the reaction kinetics of photochemical reduction of Bi³⁺. The analytical sensitivity was enhanced 30-fold using PVG for sample introduction compared to that for direct solution nebulization detection by ICP MS detection. Furthermore, the proposed method shows much better tolerance of interference from Cu²⁺ and Ni²⁺ than that from conventional hydride generation (HG). Under the optimized conditions, a detection limit of 0.3 ng L^-1 was obtained for Bi by ICP MS determination. The relative standard deviation (RSD) was 2.5% for seven replicate measurements of 0.5 ng mL^-1 Bi³⁺ standard solution. The proposed method has been successfully applied for the determination of Bi in environmental samples, including water samples, and certified reference material of soil (GSS-1) and sediments (GSD-5a and GSD-10) with satisfying results.

Photochemical Vapor Generation of Tellurium: Synergistic Effect from Ferric Ion and Nano-TiO2

Photochemical vapor generation (PVG) is emerging as a promising analytical tool for Te determination, thanks to its efficient matrix separation, and simple and green procedure. However, the low PVG generation efficiency of Te is the bottleneck for its wide application in environmental samples containing trace Te. Herein, we reported a high efficient PVG for Te determination by synergistic effect of ferric ion and nano-TiO₂. The analytical sensitivity was enhanced approximately 15-fold for Te(IV) in the presence of both ferric ions and nano-TiO₂, comparing to conventional PVG. Besides, the use of nano-TiO₂ can provide Te(VI) and Te(IV) an equal and high PVG efficiency in the presence of ferric ions, owned to the high photocatalytic performance of TiO₂ under short-wavelength UV irradiation (254 and 185 nm). Under the optimized experimental conditions, a detection limit of 1.0 ng L^-1 was obtained. The precision of replicate measurements was 2.3% (RSD, n = 7) at 0.5 μg L^-1 for Te(IV). The methodology was validated by successful determination of Te in surface waters and two standard reference sediment samples. To our best knowledge, this is the first report of the synergistic enhancement of transitional metal ions and nano-TiO₂ in PVG, which possesses potential for highly sensitive determination of vapor-forming elements.

Tellurium Distribution and Speciation in Contaminated Soils from Abandoned Mine Tailings: Comparison with Selenium

The distribution and chemical species of tellurium (Te) in contaminated soil were determined by a combination of microfocused X-ray fluorescence (μ-XRF), X-ray diffraction (μ-XRD), and X-ray absorption fine structure (μ-XAFS) techniques. Results showed that Te was present as a mixture of Te(VI) and Te(IV) species, while selenium (Se) was predominantly present in the form of Se(IV) in the soil contaminated by abandoned mine tailings. In the contaminated soil, Fe(III) hydroxides were the host phases for Se(IV), Te(IV), and Te(VI), but Te(IV) could be also retained by illite. The difference in speciation and solubility of Se and Te in soil can result from different structures of surface complexes for Se and Te onto Fe(III) hydroxides. Furthermore, our results suggest that the retention of Te(IV) in soil could be relatively weaker than that of Te(VI) due to structural incorporation of Te(VI) into Fe(III) hydroxides. These findings are of geochemical and environmental significance for better understanding the solubility, mobility, and bioavailability of Te in the surface environment. To the best of our knowledge, this is the first study reporting the speciation and host phases of Te in field soil by the μ-XRF-XRD-XAFS techniques.