Behaviour of selenium and tellurium species and their determination by ion chromatography

Summary An ion chromatographic method has been developed for the separation of Te (IV) and Se(IV) in hydrochloric acid mobile phases; the method has been used to determine tellurium in a high-purity non-stoichiometric semiconducting ZnCdTe-based material. Different cation-exchange columns (IonPac CS2, CS3, CS10), a mixed bed ion-exchange column (IonPac CS5), a multi-mode cation-exchange column (OmniPac PCX-500), anion-exchange columns (IonPac AS4, AS4A, AS5, AS5A, AS10, AS11) and a multi-mode anion-exchange column (OmniPac PAX-500) were evaluated for ion chromatographic separation of Se and Te and to study the chemical forms in which the analytes were eluted. The chromatographic data obtained enabled the calculation of both the sign and the chaarge of the eluting species.     

Application of artificial neural networks as a technique for interference removal: kinetic-spectrophotometric determination of trace amounts of Se(IV) in the presence of Te(IV)

Artificial neural networks (ANNs) are among the most popular techniques for nonlinear multivariate calibration in complicated mixtures using spectrophotometric data. In this study we propose a computer-based method for removing Te(IV) interference in the determination of Se(IV) using artificial neural networks. In this way, an artificial neural network consisting of three layers of nodes was trained by applying a back-propagation learning rule. The resulting RMSE of prediction for selenium was obtained as 0.108.     

Anion-exchange separation of Te(IV) from Te(VI), Se(IV) and Se(VI) on deae-cellulose in mixed hydrochloric-acetic acid media

Te(IV) can be separated from Te(VI), Se(IV) and Se(VI) by adsorption of Te(IV) on a DEAE-cellulose column from a mixed 1M hydrochloric acid-acetic acid solution (1:9, v/v). This allows a selective separation of Te (IV) from the other three species in widely different mole ratios.     

Nucleophilic attack by bromide ions as a first step of conversion of Se(VI) to Se(IV)

Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH₂⁺ group in the protonated form of H₂SeO₄ by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k₁[H⁺][Br⁻]^1.15[Se(IV)] the rate constant 1 × 10⁻³ L² mol⁻² s⁻¹ was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.     

Luminol Chemiluminescence with Heteropoly Acids and its Application to the Determination of Arsenate,Germanate, Phosphate and Silicate by Ion Chromatography

A flow-injection chemiluminescence (CL) method has been proposed for sensitive determination of arsenate, germanate, phosphate and silicate, after separation by ion chromatography (IC). The post-column detection system involved formation of heteropoly acid in a H₂SO₄ medium before the CL reaction with luminol in an NaOH medium. For separation, heteropoly acid formation and the CL detection reaction, pH requirements were not compatible. When present as a heteropoly acid complex with molybdenum(VI), ger- manium(IV) and silicon(IV) caused CL emission from oxidation of luminol, and such a CL oxidation of luminol was observed analogously for arsenic(V) and phosphorus(V) but with the addition of metavanadate ion to the acid solution of molybdate. Good sensitivity for the three analytes arsenic(V), ger- manium(IV) and phosphorus(V) could be given by a single set of reagent conditions, chosen carefully. Another set was suitable for determining phosphorus(V) and silicon(IV). The minimum detectable concentrations of arsenic(V), germanium(IV), phosphorus(V) and silicon(IV) were 10, 50, 1 and 10 μg l⁻¹, respectively. Linear calibrations for arsenic(V), germanium(IV), phosphorus(V) and silicon(IV) were established over the respective concentration ranges of 10–1000, 50–25000, 1–1000 and 50–1 μg l⁻¹. The proposed IC–CL method was successfully applied to analyses of a seaweed reference material, rice wine and water samples.     

Thin-Layer chromatography of inorganic ions on cellulose phosphate in sulfuric acid-organic solvent media

Summary Thin-layer chromatographic behavior of 49 inorganic ions on cellulose phosphate (P-cellulose) has systematically been surveyed with binary solvent mixtures consisting of sulfuric acid and an organic solvent such as methanol or acetone. The R_f values of many bivalent and monovalent ions as well as Te(VI) decrease on the P-cellulose layer with an increasing concentration of the organic solvent. Polyvalent ions which form strong phosphato-complexes and precipitate insoluble sulfate are strongly retained on P-cellulose. Oxy-anions, Au(III) and Pt(IV) are not adsorbed on the cellulose to any great extent. Feasibilities of the separation of multicomponent mixtures are demonstrated on the P-cellulose layer.     

High surface area Pd, Pt and Ni ion-exchanged Zr, Ti and Sn(IV) phosphates and their application to selective heterogeneous catalytic hydrogenation of alkenes

Amorphous acidic metal(IV) phosphates of zirconium, titanium and tin have been prepared and hydrogen-exchanged for bivalent Pd, Pt and Ni. These bivalent metals were returned to the zero valent state by reducing them with either hydrogen at 400 °C or with sodium tetrahydroborate at room temperature. The resulting Pd⁰, Pt⁰ and Ni⁰ phosphates were investigated as selective catalysts for heterogeneous hydrogenation of alkenes in solution at normal temperatures and pressures and, for Ni, also in the vapour phase. Quantitative studies on rates of hydrogenation are discussed. The usual methods for preparing metal(IV) phosphates give either crystalline or amorphous solids having low specific surfaces areas. A method has been developed, by which metal(IV) phosphates having large surface areas (lsa) may be prepared easily. These lsa supports take up large amounts of transition metal cations by simple exchange. The enhanced incorporation of Pd, Pt or Ni and increases in surface areas of the phosphate supports have provided some active, selective catalysts. Pd/Ti phosphates were the most active and compared well with commercial Pd on carbon. Ni/Ti phosphate is a very selective catalyst for vapour phase hydrogenation of alkenes and, at slightly higher temperatures, it is an efficient hydrocarbon cracking catalyst.     

Cathodic Stripping Voltammetric Determination of Tellurium(IV) with in situ Plated Bismuth-Film Electrode

Abstract

A very sensitive and reliable method is proposed for the determination of tellurium(IV) [Te(IV)] by Osteryoung square-wave cathodic stripping voltammetry. This method is based on the reduction of Te(IV) with bismuth(III) onto an edge-plane pyrolytic graphite electrode, followed by a cathodic potential scan. The reduced Te gave a well-defined catalytic hydrogen wave at ?1200 mV vs. Ag/AgCl. The peak height of the catalytic wave was directly proportional to the initial Te(IV) concentration in the concentration ranges of 0.01–0.10 and 0.1–1.0 µg L^?1 with 30 s deposition time. A 3σ detection limit of 1.0 ng L^?1 Te(IV) was obtained with the same deposition time. The relative standard deviation was 3% on replicate runs (n = 5) for the determination of 0.1 µg L^?1 Te(IV). Analytical results of natural water samples demonstrate that the proposed method is applicable to the determination of traces of Te(IV).     

Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line prereduction of Se(VI) to Se(IV)

An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters by hydride generation atomic absorption spectrometry with microwave-aided heating prereduction of Se(VI) to Se(IV). The samples and the prereductant solutions (4 mol l⁻¹ HCl for Se(IV) and 12 mol l⁻¹ HCl for Se(VI)) which circulated in a closed-flow circuit were injected by means of a time-based injector. This mixture was displaced by a carrier solution of 1% v/v of hydrochloric acid through a PTFE coil located inside the focused microwave oven and mixed downstream with a borohydride solution to generate the hydride. The linear ranges were 0–120 and 0–100 μg l⁻¹ of Se(IV) and Se(VI), respectively. The detection limits were 1.0 μg l⁻¹ for Se(IV) and 1.5 μg l⁻¹ for Se(VI). The precision (about 2.0–2.5% RSD) and recoveries (96–98% for Se(IV) and 94–98% for Se(VI)) were good. Total selenium values were also obtained by electrothermal atomic absorption spectrometry which agreed with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is that the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters is performed in a closed system with a minimum sample manipulation, exposure to the environment, minimum sample waste and operator attention.     

Stability of Sulfur(IV) Solutions in the Presence of Amines and the Tendency of Sulfite Ions to Disproportionate in Stock Solutions

Abstract

Several sulfite solutions at the level of 0.050 mol.L^?1 were kept at 25°C, in polyethylene flasks, in the presence and absence of air. The concentration of sulfite was periodically checked by the iodometric method. The presence of ethanolamine, ethylenediamine or tris(hydroximethyl)aminomethane, at 0.05 - 0.20 mol.L^?1 concentration levels, showed a remarkable stabilizing effect at pH values higher than 10.5. The amine ionization was supressed by the common ion effect by using OH^?, added as NaOH. The changes in the concentration of S(IV) solutions in the presence of amine were about 1 to 3 %, during the period of 85 days. The stabilizing effect depends only on the amine group and not on the mixed function alcohol/amine. It was shown that an adduct of R-NH₂.SO₂ type is not formed in aqueous medium. In the stock S(IV) solutions kept in highly alkaline medium a slow increase in pH was observed and disproportionation of sulfite ion was evidenced by formation of thiosulfate as revealed from ion chromatographic measurements. In the presence of oxygen dithionate ion is also formed.     

Simultaneous spectrophotometric determination of Sn(II) and Sn(IV) by mean centering of ratio kinetic profiles and partial least squares methods

Two spectrophotometric methods are described for the simultaneous determination of binary mixtures of Sn(II) and Sn(IV) in water samples and fruit juice samples, without prior separation steps, using the mean centering of ratio kinetic profiles and partial least squares (PLS) methods. The methods are based on the difference in the rate of the reactions of Sn(II) and Sn(IV) with pyrocatechol violet at pH 4.0. The methods allow rapid and accurate determination of Sn(II) and Sn(IV). The analytical characteristics of the methods for the simultaneous determination of binary mixtures of Sn(II) and Sn(IV) were calculated. The results showed that the methods were capable to simultaneous determination of 0.1–1.80 mg L⁻¹ each of cations. The proposed methods were successfully applied to the simultaneous determination of Sn(II) and Sn(IV)in an orange juice sample.     

Stability of selenium and its speciation analysis in water using automatic system separation and HR-ICP-MS measurement

A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) measurement. ⁷⁵Se(IV) and ⁷⁵Se(VI) were prepared and used as tracers during the experiments. The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure. The parameters which affect the uptake of Se(IV) and Se(VI) on Dowex1 × 8 resin was optimized and the procedure for Se(IV) and Se(VI) separation was proposed. Both Se(IV) and Se(VI) are retained on the column in natural or alkaline solution with high distribution coefficient. The successive gradient elution of pre-concentrated species of selenium with HNO₃ solution allows to differentiate between them. Se(IV) and Se(VI) finally were eluted with 0.05 mol/L HNO₃ and 5.0 mol/L HNO₃, respectively. The proposed method has been successfully verified using the certified reference materials (CRMs) of real water samples, and spiked recoveries for real samples were 98%-104% with 5% relative standard deviations (RSDs). The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.     

On line speciation of Se(VI), Se(IV), and trimethylselenium by HPLC-microwave oven-hydride generation-atomic absorption spectrometry

An on-line system is proposed consisting of an anion-exchange chromatographic column, microwave-induced thermooxidation of trimethylselenium in the presence of persulphate, and microwave-induced thermoreduction of Se(VI) to Se(IV) in HCl medium, followed by hydride generation and atomic absorption for the determination of trimethylselenium (TMeSe), Se(IV) and Se(VI). Trimethylselenium is eluted in the dead volume of an anion-exchange column (Hamilton PRP-X-100), before elution of Se(IV) and Se(VI). Optimum chromatographic conditions have been obtained using 100 mmol L^–1 phosphate buffer (pH=6.8) H₂PO ₄ ^– /HPO ₄ ^2– as the mobile phase. Recoveries were around 100%, absolute detection limits were 1.1, 1.4 and 2.2 ng for TMeSe, Se(IV) and Se(VI), respectively. Precision was lower than 10% in all cases. The method has been applied to tap water.     

Selektive Extraktion von Tellur mit Di-n-oktylsulfoxid

Zusammenfassung Über die Ergebnisse der Extraktion von Tellur und Selen aus stark salzsauren Lösungen mit Tri-n-butylphosphat, Tri-n-oktylphosphinoxid, Dibenzylsulfoxid und Di-n-oktylsulfoxid wurde berichtet. Von diesen stark solvatisierenden Reagenzien ist das Di-n-oktylsulfoxid zur Extraktion von Te(IV) und dessen Trennung von Se(IV) sowie von vielen anderen Elementen am besten geeignet. Eine Vorextraktion mit Diisopropyläther und der Einsatz von Fluorid als Maskierungsmittel ergeben in Kombination mit der Extraktion durch Di-n-oktylsulfoxid einen sehr selektiven Trenngang zur Anreicherung von Tellur durch Extraktion aus stark salzsaurer Lösung.

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Selective extraction of tellurium with Di-n-octylsulfoxide

Summary The results of extraction of tellurium and selenium from strong hydrochloric acid solutions with tri-n-butylphosphate, tri-n-octylphosphineoxide, dibenzylsulfoxide and di-n-octylsulfoxide were reported. Of these highly solvatizing reagents, di-n-octylsulfoxide is most suitable for extraction of Te(IV) and its separation from Se(IV) as well as from many other elements. A pre-extraction with di-isopropyl ether and the use of fluoride as masking agent give rise to a highly selective separation for enrichment of tellurium by extraction from a strong hydrochloric acid solution in combination with extraction by di-n-octylsulfoxide.

     

Determination of selenium(IV) and tellurium(IV) by differential pulse polarography

Differential pulse polarographic methods for the determination of selenium(IV) and tellurium(IV) in nitric acid medium are described. The peak current is maximal when 0.25M nitric acid medium is used, the DPP peaks for Se(IV) and Te(IV) being at -0.54 and -0.8 V vs. Ag/AgCl respectively. The peak current is a linear function of selenium concentration over three ranges, 5.1 x 10(-6)-1.3 x 10(-5), 1.27 x 10(-5)-1.27 x 10(-4) and 1.27 x 10(-4)-7.60 x 10(-4)M Se(IV), with different slopes. The plot for Te(IV) is linear over the range 0.78 x 10(-6)-9.40 x 10(-5)M.     

Non-chromatographic hydride generation atomic spectrometric techniques for the speciation analysis of arsenic,antimony, selenium,and tellurium in water samples—a review

Hydride generation (HG) coupled with AAS, ICP–AES, and AFS techniques for the speciation analysis of As, Sb, Se, and Te in environmental water samples is reviewed. Careful control of experimental conditions, offline/online sample pretreatment methods employing batch, continuous and flow-injection techniques, and cryogenic trapping of hydrides enable the determination of various species of hydride-forming elements without the use of chromatographic separation. Other non-chromatographic approaches include solvent extraction, ion exchange, and selective retention by microorganisms. Sample pretreatment, pH dependency of HG, and control of NaBH₄/HCl concentration facilitate the determination of As(III), As(V), monomethylarsonate (MMA), and dimethylarsinate (DMA) species. Inorganic species of arsenic are dominant in terrestrial waters, whereas inorganic and methylated species are reported in seawater. Selenium and tellurium speciation analysis is based on the hydrides generation only from the tetravalent state. Se(IV) and Se(VI) are the inorganic selenium species mostly reported in environmental samples, whereas speciation of tellurium is rarely reported. Antimony speciation analysis is based on the slow kinetics of hydride formation from the pentavalent state and is mainly reported in seawater samples.     

Differential pulse voltammetric determination of trace Te(IV) at a poly(3,3′-diaminobenzidine) film modified gold electrode in flow systems

Electropolymerization of 3,3′-diaminobenzidine on a gold surface gave an adherent, stable film of poly(3,3′-diaminobenzidine) (PDAB). This polymer film retained the complexational functionalities of its monomer, demonstrating preconcentration abilities for several ions, including Se(IV) and Te(IV). In particular, in this work, continuous flow and flow injection methods were developed for the sensitive and selective determination of Te(IV). The optimized method for the continuous flow mode had a detection limit of 5.6×10⁻⁹ mol l⁻¹ for 10 min preconcentration. Typical relative standard deviations for six consecutive determinations were 1.82 and 2.56% for Te(IV) concentrations of 1.0×10⁻⁶ and 5.0×10⁻⁸ mol l⁻¹, respectively (10 min preconcentration). The method was applied to the determination of Te(IV) in real samples.     

Kinetic spectrophotometric method for simultaneous determination of selenium and tellurium using partial least squares calibration

A kinetic-spectrophotometric method for the simultaneous determination of Se(IV) and Te(IV) is described. The method is based upon the catalytic effect of these cations on the reaction of toluidine blue with sulfide. Partial least squares calibration method was employed for the data manipulation and analysis. The concentrations were varied between 0.02-0.24 and 0.01-0.08 μg/ml for Se(IV) and Te(IV), respectively. Cross-validation method was used to select the optimum number of factors (NF). The root mean square errors of difference for selenium and tellurium were 1.2 and 1.7 μg/ml, respectively. Application of the method to artificial samples and several mixtures of standard solutions of Se(IV) and Te(IV) were performed and satisfactory results were obtained.     

Front Cover: Synthesis,Characterization, and Cytotoxicity of a Reactive Platinum(IV) Monotrifluoromethyl Complex (Eur. J. Inorg. Chem. 3/2023)

Platinum-based complexes are among the most widely utilized cancer therapeutics. Current Pt(II) drugs face some challenges including toxicity and drug resistance. To solve these issues, great efforts have been devoted to developing nonclassical platinum complexes, such as Pt(IV) prodrugs, that act via mechanisms distinct from those of the approved drugs. Compared with active Pt(II) counterparts, Pt(IV) complexes are relatively inert. Although direct interactions between Pt(IV) complexes and nucleotides have been reported, the reaction is slow due to the kinetic inertness of Pt(IV) complexes. Herein, we design and synthesize a Pt(IV) monotrifluoromethyl complex, in which the chloride ligand that is trans to trifluoromethyl ligand is reactive. The Pt(IV) monotrifluoromethyl complex is very stable in water but displays high reactivity towards various substrates including buffer components and 5’-dGMP. The study of reaction mechanism reveals that this Pt(IV) complex reacts with phosphate via S_N2 nucleophilic substitution pathway, which is different from Pt(II) drugs. The Pt(IV) monotrifluoromethyl complex is cytotoxic in human ovarian cancer cells. Our work reports an example of a reactive organometallic Pt(IV) complex that can directly interact with nucleophiles and implies its potential as an anticancer agent.     

Chromatographic behaviour of metal ions on tin(IV) and titanium(IV) antimonate papers

Summary The chromatographic behaviour of 49 metal ions has been studied on papers impregnated with Sn(IV) and Ti(IV) antimonates in aqueous HNO₃ and mixed solvent systems containing dimethyl sulphoxide. Numerous separations have been achieved and the Alberti equation, for Sn(IV) and Ti(IV) antimonate papers, in the modified form: –nloga K⁺=R_M + constant (a K⁺=activity of K⁺), has been verified. The effect of the concentration of impregnating reagents on these papers has been determined and compared with other papers. The effect of pH on R_f, R_i, log R_f and R_M values of metal ions has also been examined in aqueous systems.