Studying the effect of an ionic liquid on cloud point extraction technique for highly efficient preconcentration and speciation analysis of tellurium in water, soil and sediment samples

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.

Innovative approaches in cloud-point extraction

Cloud-point extraction (CPE) is a pre-treatment technique for the extraction and preconcentration of different chemical compounds, such as metal ions, pesticides, drugs, phenols, vitamins etc., from various samples. CPE is based on the phenomenon of two phases (micellar and aqueous) forming after the heating of an aqueous isotropic solution of a non-ionic or zwitterionic surfactant above the cloud-point temperature. If analytes are added to the surfactant solution under suitable conditions, they should be extracted into the micellar phase, also called the surfactant-rich phase. Recently, the traditional CPE procedure is being increasingly replaced by improved CPE procedures. In this study, recent advances in CPE over the last three years (2020 - 2022), including the application of various innovative approaches, are reviewed. In addition to the basic principle of CPE, alternative extraction media in CPE, CPE supported by various auxiliary energies, a different modified CPE procedure and the use nanomaterials and solid-phase extraction in combination with CPE are presented and discussed. Finally, some future trends for improved CPE are presented.

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.

Elemental Speciation Analysis in Environmental Studies: Latest Trends and Ecological Impact

Speciation analysis is a key aspect of modern analytical chemistry, as the toxicity, environmental mobility, and bioavailability of elemental analytes are known to depend strongly on an element’s chemical species. Henceforth, great efforts have been made in recent years to develop methods that allow not only the determination of elements as a whole, but also each of its separate species. Environmental analytical chemistry has not ignored this trend, and this review aims to summarize the latest methods and techniques developed with this purpose. From the perspective of each relevant element and highlighting the importance of their speciation analysis, different sample treatment methods are introduced and described, with the spotlight on the use of modern nanomaterials and novel solvents in solid phase and liquid-liquid microextractions. In addition, an in-depth discussion of instrumental techniques aimed both at the separation and quantification of metal and metalloid species is presented, ranging from chromatographic separations to electro-chemical speciation analysis. Special emphasis is made throughout this work on the greenness of these developments, considering their alignment with the precepts of the Green Chemistry concept and critically reviewing their environmental impact.

Multi-ion imprinted polymers (MIIPs) for simultaneous extraction and preconcentration of Sb(III), Te(IV), Pb(II) and Cd(II) ions from drinking water sources

Simultaneous extraction and preconcentration of several potentially toxic metal ions have received great attention because of their toxicological effects on aquatic life and human beings. Multi-ion imprinted polymers (MIIP) have proved to be promising adsorbents with excellent specific recognition performance than single-ion imprinted polymer. Therefore, in this study, the MIIP strategy was employed for simultaneous extraction and enrichment of Sb(III), Cd(II), Pb(II) and Te(IV) ions from drinking water sources. MIIPs was used as a sorbent material in ultrasound-assisted dispersive solid phase extraction combined with inductively coupled plasma optical emission spectrometry (UA-DSPE/ICP-OES). The experimental parameters that affect the extraction efficiency and recovery of Sb(III), Cd(II), Pb(II) and Te(IV) were investigated using response surface methodology. Under optimum conditions, the enhancement factors, linear range, limit of detection (LOD) and limit of quantification (LOQ) were 37.7-51.1, 0.04-100 µg L^-1, 0.011-0.28 µg L^-1, 0.037-093 µg L^-1, respectively. The intra-day (n = 10) and inter-day (n = 5) precision expressed as relative standard deviations (%RSDs,) were 3% and 5%, respectively. The proposed UA-DSPE/ICP-OES method was applied for preconcentration and determination of the trace metal ions in environmental samples. Furthermore, the accuracy of the method was evaluated using spiked recovery experiments and the percentage recoveries ranged from 95% to 99.3%.

Preparation of environmental samples for chemical speciation of metal/metalloids: A review of extraction techniques

Chemical speciation is a relevant topic in environmental chemistry since the (eco)toxicity, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). Maintaining the chemical stability of the species and avoiding equilibrium disruptions during the sample treatment is one of the biggest challenges in chemical speciation, especially in environmental matrices where the level of concomitants/interferents is normally high. To achieve this task, strategies based on chemical properties of the species can be carried out and pre-concentration techniques are often needed due to the low concentration ranges of many species (μg L^-1 - ng L^-1). Due to the significance of the topic and the lack of reviews dealing with sample preparation of metal (loid)s (usually, sample preparation reviews focus on the total metal content), this work is presented. This review gives an up-to-date overview of the most common sample preparation techniques for environmental samples (water, soil, and sediments), with a focus on speciation of metal/metalloids and determination by spectrometric techniques. Description of the methods is given, and the most recent applications (last 10 years) are presented.