Rapid speciation of Se(IV) and Se(VI) by flow injection–capillary electrophoresis system with contactless conductivity detection

A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L^–1 and 7.5 g L^–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.     

Cobalt Chalcogenide Clusters. Synthesis,Characterization and DFT Calculations of [Co4Se2(CO)10] and [Co4Te2(CO)11]. Crystal Structure of [Co8Se4(CO)16(μ‐dppa)2]

The reactions of [Co₂(CO)₈] with E(SiMe₃)₂ (E = Se, Te) in CH₂Cl₂ result in the formation of the compounds [Co₄Se₂(CO)₁₀]> ( 1 ) and [Co₄Te₂(CO)₁₁] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ₄‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ₂‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph₂PC≡CPPh₂ (dppa), the reaction of [Co₂(CO)₈] with Se(SiMe₃)₂ leads to the formation of [Co₈Se₄(CO)₁₆(μ‐dppa)₂] ( 3 ). During the reaction two molecules of [Co₂(CO)₈] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ₃‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups.     

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 g g^–1 dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.     

Phosphaniminato-Trichloroselenate(II): Synthese und Kristallstrukturen von [SeCl(NPPh3)2]+SeCl3− und [Me3SiN(H)PMe3]2+[Se2Cl6]2−

Phosphorane Iminato-Trichloroselenates(II): Syntheses and Crystal Structures of [SeCl(NPPh₃)₂]⁺SeCl₃^? and [Me₃SiN(H)PMe₃]₂⁺[Se₂Cl₆]^2? [SeCl(NPPh₃)₂]⁺SeCl₃^? has been synthesized by the reaction of Se₂Cl₂ with Me₃SiNPPh₃ in acetonitrile solution, forming orangered crystals, whereas red crystals of [Me₃SiN(H)PMe₃]₂⁺[Se₂Cl₆]^2? were obtained by the reaction of Me₃SiNPMe₃ with SeOCl₂ in acetonitrile solution. Both complexes were characterized by X-ray structure determinations. [SeCl(NPPh₃)₂]⁺SeCl₃^?: Space group P2₁/n, Z = 4, structure solution with 7 489 observed unique reflections, R = 0.057. Lattice dimensions at ?60°C: a = 1 117.0; b = 2 241, c = 1 407.5 pm, β = 95.61°. In the cation [SeCl(NPPh₃)₂]⁺ the selenium atom is φ-tetrahedrally coordinated by the chlorine atom and by the nitrogen atoms of the phosphorane iminato ligands, whereas the anion SeCl₃^? has a T-shaped structure with φ-trigonal-bipyramidale surrounding of the selenium atom. [Me₃SiN(H)PMe₃]₂⁺[Se₂Cl₆]^2?: Space group P2₁/c, Z = 4, structure solution with 2 093 observed unique reflections, R = 0.080. Lattice dimensions at ?70°C: a = 956, b = 828, c = 1 973 pm, β = 93.80°. The structure consists of [Me₃SiN(H)PMe₃]⁺ ions and planar [Se₂Cl₆]^2? anions, in which the selenium atoms are bridged nearly symmetrically by two chlorine atoms.     

Optimisation of ICPMS collision/reaction cell conditions for the simultaneous removal of argon based interferences of arsenic and selenium in water samples

The optimisation of ICPMS collision/reaction cell conditions for the simultaneous analysis of arsenic and selenium is described. A mixture of 3.8 mL min⁻¹ of H₂ and 0.5 mL min⁻¹ of He was found to be suitable for the removal of both ArAr⁺ and ArCl⁺ interferences. Detection limits down to 30 ng (element) L⁻¹ in total analysis, and between 81 and 230 ng (element) L⁻¹ in speciation analysis were achieved in chloride matrix (1 g L⁻¹ NaCl). After validation, the method was applied to commercially available mineral waters.     

白肋烟中硒的赋存形态及分布研究

研究了叶面喷施补硒盆栽白肋烟叶中硒的赋存形态和含量分布,结果表明:叶片吸收的无机硒进入白肋烟体内代谢、转化为多种形态有机硒,叶中的核酸、多糖和蛋白质结合硒是硒的主要赋存形态,分别占总硒量的74.54%,10.95%,2.30%,生物大分子有机硒占总硒量的87%以上;在蛋白质的分级盐析组分中,其硒的分布为:D>C>B>E>A(即80%、70%、60%、95%、50%硫酸铵饱和度),分别占蛋白质结合硒的41.05%、26.49%、21.46%、12.81%、0.25%.     

硒对大豆苗期生长的影响

通过盆栽土培，以亚硒酸钠的形式供给不同水平的硒，研究了硒对大豆苗期的生物学特性、根系活力、叶绿素和可溶性蛋白质质量分数的影响，结果显示：当补硒浓度为0～1mg／g时，各项指标的变化均与硒浓度呈正相关，超过1mg／g后则反向变化；但在10mg／g以下，各项指标水平均优于未施硒的．     

Tandem and chemoselective synthesis of benzil derivatives from styrene and arene diazonium salts

A facile and practically applied protocol for synthesis of benzil derivatives using styrene and arene diazonium salts is reported. Pd(OAc)₂/SeO₂ catalytic system was found to be efficient for chemoselective synthesis of benzil. Selenium dioxide works well as an oxidant under milder reaction conditions. Moderate to very good yields of the desired products were obtained.