Dimethylselenide Research Articles

Influence of Carbon in Metalorganic Chemical Vapor Deposition of Few-Layer WSe2 Thin Films

Metalorganic chemical vapor deposition (MOCVD) is a promising technique to form large-area, uniform films of monolayer or few-layer transition metal dichalcogenide (TMD) thin films; however, unintentional carbon incorporation is a concern. In this work, we report the presence of a defective graphene layer that forms simultaneously during MOCVD growth of tungsten diselenide (WSe2) on sapphire at high growth temperature and high Se:W ratio when using tungsten hexacarbonyl (W(CO)6) and dimethyl selenide ((CH3)2Se, DMSe) as precursors. The graphene layer alters the surface energy of the substrate reducing the lateral growth and coalescence of WSe2 domains. The use of hydrogen selenide (H2Se) instead of DMSe eliminates the defective graphene layer enabling coalesced monolayer and few-layer WSe2 films.

Determination of dimethyl selenide and dimethyl sulphide compounds causing off-flavours in bottled mineral waters

Sales of bottled drinking water have shown a large growth during the last two decades due to the general belief that this kind of water is healthier, its flavour is better and its consumption risk is lower than that of tap water. Due to the previous points, consumers are more demanding with bottled mineral water, especially when dealing with its organoleptic properties, like taste and odour. This work studies the compounds that can generate obnoxious smells, and that consumers have described like swampy, rotten eggs, sulphurous, cooked vegetable or cabbage. Closed loop stripping analysis (CLSA) has been used as a pre-concentration method for the analysis of off-flavour compounds in water followed by identification and quantification by means of GC-MS. Several bottled water with the aforementioned smells showed the presence of volatile dimethyl selenides and dimethyl sulphides, whose concentrations ranged, respectively, from 4 to 20 ng/L and from 1 to 63 ng/L. The low odour threshold concentrations (OTCs) of both organic selenide and sulphide derivatives prove that several objectionable odours in bottled waters arise from them. Microbial loads inherent to water sources, along with some critical conditions in water processing, could contribute to the formation of these compounds. There are few studies about volatile organic compounds in bottled drinking water and, at the best of our knowledge, this is the first study reporting the presence of dimethyl selenides and dimethyl sulphides causing odour problems in bottled waters.

Volatile selenium fluxes from selenium-contaminated sediments in an Australian coastal lake

Environmental context Methylation of sedimentary selenium to volatile dimethylselenide is a natural remediation process for contaminated aquatic systems. We present flux estimates for the loss of dimethylselenide from sediments of an anthropogenically affected lake and observe a 6-fold difference between late autumn–early winter and summer. The loss of dimethylselenide represents a significant sediment loss vector, of the same order as the diffusive loss flux for inorganic selenium across the sediment–water interface. Abstract Overflows from ash dams associated with the operation of coal-fired power stations in Lake Macquarie, NSW, Australia, have been a historical source of selenium to the lake. Although dissolved selenium concentrations have been marginally elevated, sediments are the major sink. Methylation of sedimentary selenium to volatile dimethylselenide (DMSe) is known to be a natural remediation process. Sediments from north of Wyee Bay and the Vales Point Power Station were the subject of field sampling and monitoring to determine the extent to which selenium is being lost to the atmosphere as DMSe. Flux estimates were obtained by trapping volatile selenium species using benthic domes, followed by analysis in the field using a fully automated cryogenic trapping system with atomic fluorescence detection. The detection limit of the system was 0.1ngL–1 for DMSe and 1ngL–1 for dimethyl diselenide (DMDSe). Measurements in both summer and late autumn–early winter showed a distinct seasonal difference, with a higher summer DMSe flux of 53±25ng Se m–2h–1 (±s.d.) compared with 8±5ng Se m–2h–1 in late autumn–early winter. No DMDSe was detected. These fluxes are similar to those measured in Europe and North America, and represent an annual loss of 1.3kg of selenium per year from the nearby lake area. Lake-wide this would represent a significant loss to the atmosphere.

Quantification of volatile-alkylated selenium and sulfur in complex aqueous media using solid-phase microextraction

Biologically produced volatile-alkylated Se and S compounds play an important role in the global biogeochemical Se and S cycles, are important constituents of odorous industrial emissions, and contribute to (off-)flavors in food and beverages. This study presents a fully automated direct-immersion solid-phase microextraction (DI-SPME) method coupled with capillary gas chromatography−mass spectrometry (GC/MS) for the simultaneous quantification of 10 volatile-alkylated Se and S compounds in complex aqueous media. Instrumental parameters of the SPME procedure were optimized to yield extraction efficiencies of up to 96% from complex aqueous matrices. The effects of sample matrix composition and analyte transformation during sample storage were critically assessed. With the use of internal standards and procedural calibrations, the DI-SPME−GC/MS method allows for trace-level quantification of volatile Se and S compounds in the ng/L range (e.g. down to 30ng/L dimethyl sulfide and 75ng/L dimethyl selenide). The applicability and robustness of the presented method demonstrate that the method may be used to quantify volatile Se and S compounds in complex aqueous samples, such as industrial effluents or food and beverage samples.

Methylation of Thiols and Thioethers by Human Indolethylamine‐N Methyl Transferase

Indolethylamine‐N MethylTransferase (INMT) is a small molecule N‐methyltransferase that transfer methyl groups from S‐Adenosyl‐L‐Methionine (SAM) to indoleamines. Methylation of tryptamine produces the hallucinogen, N,N‐dimethyltryptamine (DMT), and methylated serotonin generates bufotenin. In animals, the endogenous production of DMT has been proposed to be a regulator of the Sigma‐1 Receptor and for mood and cognition through activation of serotonin and other receptors. In contrast to the human and rabbit INMT, mouse INMT (referred to as ThioEtherMethylTransferase or TEMT) has been independently characterized and methylates thioethers, dimethyl selenide and dimethyl telluride to produce their respective “onium “ products. TEMT was suggested to be involved in the detoxification of sulfides, selenides, and tellurides. The S‐methylating activities of human and rabbit INMT have not been characterized. We evaluated the efficiency of human INMT to produce methylated sulfur containing compounds. Pure human INMT methylated both thiols and thioethers including cysteamine and 2‐(thiomethyl)ethylamine (MTEA). The Km for MTEA methylation at pH 7.2 was approximately 1.2 mM. We also compared the N‐ and S‐methylating activities of human INMT over a pH range of 6.3‐8.0 and found that acidic conditions favored S‐methylation of MTEA and alkaline conditions favored N‐methylation of tryptamine. The methylations of tryptamine and MTEA were approximately equal at pH 6.8. These data suggest a mechanism of cellular regulation of the bifunctional N‐ and S‐methylating activities of human INMT that may depend on the prevailing acidic and basic conditions of certain mammalian tissues.

Product ion distributions for the reactions of NO(+) with some physiologically significant volatile organosulfur and organoselenium compounds obtained using a selective reagent ionization time-of-flight mass spectrometer.

RATIONALEThe reactions of NO+ with volatile organic compounds (VOCs) in Selective Reagent Ionization Time-of-Flight Mass Spectrometry (SRI-TOF-MS) reactors are relatively poorly known, inhibiting their use for trace gas analysis. The rationale for this product ion distribution study was to identify the major product ions of the reactions of NO+ ions with 13 organosulfur compounds and 2 organoselenium compounds in an SRI-TOF-MS instrument and thus to prepare the way for their analysis in exhaled breath, in skin emanations and in the headspace of urine, blood and cell and bacterial cultures.METHODSProduct ion distributions have been investigated by a SRI-TOF-MS instrument at an E/N in the drift tube reactor of 130 Td for both dry air and humid air (4.9% absolute humidity) used as the matrix gas. The investigated species were five monosulfides (dimethyl sulfide, ethyl methyl sulfide, methyl propyl sulfide, allyl methyl sulfide and methyl 5-methyl-2-furyl sulfide), dimethyl disulfide, dimethyl trisulfide, thiophene, 2-methylthiophene, 3-methylthiophene, methanethiol, allyl isothiocyanate, dimethyl sulfoxide, and two selenium compounds – dimethyl selenide and dimethyl diselenide.RESULTSCharge transfer was seen to be the dominant reaction mechanism in all reactions under study forming the M+ cations. For methanethiol and allyl isothiocyanate significant fractions were also observed of the stable adduct ions NO+M, formed by ion-molecule association, and [M–H]+ ions, formed by hydride ion transfer. Several other minor product channels are seen for most reactions indicating that the nascent excited intermediate (NOM)+* adduct ions partially fragment along other channels, most commonly by the elimination of neutral CH3, CH4 and/or C2H4 species that are probably bound to an NO molecule. Humidity had little effect on the product ion distributions.CONCLUSIONSThe findings of this study are of particular importance for data interpretation in studies of volatile organosulfur and volatile organoselenium compounds employing SRI-TOF-MS in the NO+ mode. © 2014 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.

Improving pulsed radiofrequency glow discharge for time-of-flight mass spectrometry simultaneous elemental and molecular analysis

The performance of radiofrequency (rf) millisecond pulsed glow discharge (PGD) coupled to a fast orthogonal time-of-flight mass spectrometer (TOFMS) for chemical characterization and quantification of organic volatile compounds was investigated by using two different GD chamber designs. The designs investigated had substantial differences in the way that the volatile organic compound is introduced into the GD and the distance between the cathode and the sampling cone of the mass spectrometer. Bromochloromethane was selected as the model analyte because of the practical interest of determining trihalomethanes at low concentrations, and also because of both its low boiling point (to avoid problems associated with condensations in the interface) and the fact that it has two different heteroatoms, making the fragmentation patterns easier to follow. Pulse shapes of element, fragment, and molecular parent ions obtained by using the two GD chambers under investigation were critically compared. Results revealed the critical effect of the GD chamber geometry in obtaining the three types of chemical information, temporally discriminated. The spectra of the gaseous samples and of a polymer containing TBBPA (solid sample) were also compared. Detection limits for bromochloromethane in the order of low ng L(-1), and the required high tolerance of the plasmas to the introduction of organic vapours, were achieved using one of the proposed GD designs. The capability of the designed system for the analysis of other volatile compounds, for example dimethyl disulfide and dimethyl selenide, was also successfully evaluated, making use of the analytical potential of the information obtained from the different pulse time regions.

Dimethyl selenide complexes with compounds of Group IIIA elements: electron density redistribution and interaction energy partitioning

Molecular structures of dimethyl selenide complexes with AX3 (A = B, Al, Ga, In; X = H, Me) compounds of Group IIIA elements were calculated by the PBE1PBE/Sapporo-TZ method. A complex approach to study the nature of interactions is proposed, which involves analysis of electron localization/delocalization characteristics and their influence on charge transfer and energy effects of complexation. It is shown that electron sharing is more important for stabilization of the complexes under study than electrostatic interaction between their fragments. It is demonstrated that analysis of local (topological) characteristics of the electron density distribution is insufficient to discover similarity/dissimilarity in the nature of some complexes. The energies of interaction in the complexes under study are mainly composed of the contributions of Se atom as active center of the donor molecule and the entire acceptor molecule. Energy characteristics of local interaction between Se atom and Group IIIA element atom are not representative.

Compact integration of gas chromatographer and atomic fluorescence spectrometer for speciation analysis of trace alkyl metals/semimetals

Gas chromatographic separation was coupled with atomic fluorescence spectrometry (GC–AFS) directly via argon-hydrogen flame for integrated GC–AFS instrumentation, i.e., the outlet end of the GC column was directly put into the bottom of the Ar-H2 flame atomizer without any transportation interface. This laboratory-constructed GC–AFS instrument was preliminarily characterized by its application for the speciation analysis of dimethyl selenide ((Met)2Se) and dimethyl diselenide ((Met)2Se2) as well as the two-channel simultaneous determination of tetramethyl tin (Sn(Met)4) and tetraethyl lead (Pb(Et)4). Under the optimized experimental conditions, the absolute limits of detection of 9.4pg for (Met)2Se, 3.8pg for (Met)2Se2, 0.23ng for Sn(Met)4 and 0.39ng for Pb(Et)4 were obtained. The coupling is simple, and the whole instrument is compact.

Dinuclear niobium(III) and tantalum(III) complexes with thioether and selenoether ligands [{MIIIX2(L)}2(μ-X)2(μ-L)] (M = Nb, Ta; X = Cl, Br; L = R2S, R2Se): Syntheses, structures, and the optimal conditions and the mechanism of the catalysis for regioselective cyclotrimerization of alkynes

A series of dinuclear niobium(III) and tantalum(III) halide complexes with chalcogen donors [{MIIIX2(L)}2(μ-X)2(μ-L)] (M = Nb; X = Cl, Br; L = R2S, R2Se) (M = Ta; X = Cl, Br; L = R2S) have been prepared by the reaction of dimetal(V) decahalide (M2X10) with magnesium and L. The structures of five of those new complexes were determined by X-ray crystallography to have a M–M double bond. It is evidenced that the solvent and the temperature play important roles in achieving high yield and regioselectivity for cyclotrimerization of alkynes. The reaction of the niobium(III) chloride complexes (L = dimethyl sulfide (Me2S), tetrahydrothiophene (C4H8S, THT, thiolane)) with phenylacetylene at room temperature in toluene gave both head-to-tail cycloadded trimers of alkyne, 1,3,5-(Ph)3-2,4,6-(H)3-benzene and head-to-head cycloadded 1,2,4-(Ph)3-3,5,6-(H)3-benzene, in high yields. The smaller the thioether ligands, the higher the catalytic activity. The niobium(III) chloride complexes with selenoether (L = dimethyl selenide (Me2Se), tetrahydroselenophene (C4H8Se, THSe, selenolane) have higher rates for the reaction with alkynes, but low activity for the cyclotrimerization. Tantalum(III) chloride complexes (L = Me2S, THT, tetrahydrothiopyran (C5H10S, THTP, thiane)) have lower catalytic activities than the niobium(III) ones, because the Ta–S(μ-L) bond lengths are shorter than those of niobium analogs. The stability of the precursor complexes toward the first oxidative addition depends on the M–S(μ-L) bond strength, and controls the concentration of catalytic active species. The niobium(III) bromide complexes (L = Me2S, THT) and the tantalum(III) bromide one (L = Me2S) react with alkynes to give head-to-tail compounds regioselectively, but are less catalytically active than those of chloride complexes.

Head space solid phase microextraction based on nano-structured lead dioxide: Application to the speciation of volatile organoselenium in environmental and biological samples

A novel and efficient speciation method based on the nano-structured lead dioxide as stationary phase of head space solid phase microextraction combined with gas chromatography mass spectrometry (GC–MS) was developed for the determination of volatile organoselenium compounds (dimethylselenide (DMSe) and dimethyldiselenide (DMDSe)) in different biological and environmental samples. PbO2 particles with a diameter in the range of 50–70nm have been grown on platinum wire via elechtrochemical deposition. The effect of different variables on the extraction efficiency was studied simultaneously using an experimental design. The variables of interest in the HS-SPME were condition of coating preparation, desorption time, stirring rate, desorption temperature, ionic strength, time and temperature of extraction. A Plackett–Burman design was performed for screening in order to determine the significant variables affecting the extraction efficiency. Then, the significant factors were optimized by a Box–Behnken design (BBD) and the response surface equations were derived. The detection limit and relative standard deviation (RSD) (n=5, c=50μgL−1) for DMSe were 16ngL−1 and 4.3%, respectively. They were also obtained for DMDSe as 11ngL−1 and 4.6%, respectively. The developed technique was found to be applicable to spiked environmental and biological samples.

An ab initio and DFT study of homolytic substitution reactions by oxyacyl radicals at sulfur, selenium, and tellurium

Homolytic substitution reactions of methoxycarbonyl radicals at the sulfur, selenium, and tellurium atoms in dimethyl sulfide, dimethyl selenide, and dimethyl telluride have been investigated using computational techniques. Ab initio and DFT calculations predict that attack of methoxycarbonyl radical at the sulfur and selenium containing molecules proceed via smooth transition states without the involvement of hypervalent intermediates. BHandHLYP/DZP calculated energy barriers (ΔE‡) for these reactions range from 58.3 (S) to 34.6 (Se)kJmol−1. In contrast, calculations on the analogous reaction involving tellurium predict the involvement of an intermediate at MP2/DZP. BHandHLYP/DZP calculations provide an energy barrier (ΔE‡) of 7.7kJmol−1 for the reaction involving tellurium. These homolytic substitution reactions are predicted to be exothermic at all levels of theory with the forward reactions favoured by 11–28kJmol−1 for attack at sulfur, 4–23kJmol−1 for attack at selenium and by only 1–3kJmol−1 for attack at tellurium.

A Study of the Atmospherically Important Reactions between Dimethyl Selenide (DMSe) and Molecular Halogens (X2 = Cl2, Br2, and I2) with ab initio Calculations

The atmospherically relevant reactions between dimethyl selenide (DMSe) and the molecular halogens (X(2) = Cl(2), Br(2), and I(2)) have been studied with ab initio calculations at the MP2/aug-cc-pVDZ level of theory. Geometry optimization calculations showed that the reactions proceed from the reagents to the products (CH(3)SeCH(2)X + HX) via three minima, a van der Waals adduct (DMSe:X(2)), a covalently bound intermediate (DMSeX(2)), and a product-like complex (CH(3)SeCH(2)X:HX). The computed potential energy surfaces are used to predict what molecular species are likely to be observed in spectroscopic experiments such as gas-phase photoelectron spectroscopy and infrared matrix isolation spectroscopy. It is concluded that, for the reactions of DMSe with Cl(2) and Br(2), the covalent intermediate should be seen in spectroscopic experiments, whereas, in the DMSe + I(2) reaction, the van der Waals adduct DMSe:I(2) should be observed. Comparison is made with previous related calculations and experiments on dimethyl sulfide (DMS) with molecular halogens. The relevance of the results to atmospheric chemistry is discussed. The DMSeX(2) and DMSe:X(2) intermediates are likely to be reservoirs of molecular halogens in the atmosphere which will lead on photolysis to ozone depletion.

Determination of dimethylsulfide and dimethylselenide in human urine by portable gas chromatography–photoionization detection with headspace sampling

A simple and sensitive method for the determination of dimethylsulfide (DMS) and dimethylselenide (DMSe) employing a gas chromatograph–photoionization detector with headspace sampling (HS-GC-PID) was developed. Parameters affecting the HS-GC-PID sensitivity including matrix effect, heating temperature, extraction time and carrier gas flow-rate were optimized. The matrix effect was required for standard addition calibration method for quantification purposes. The method has been validated when rectilinear relationship was between the concentrations of analytes and peak area in the range of 0.2–50ngmL−1 for DMSe and 0.5–100ngmL−1 for DMS, the correlation coefficients were from 0.995–0.998, and the limits of detection for DMS and DMSe were 25pgmL−1 and 48pgmL−1, respectively. The proposed method was further applied to quantification of DMS and DMSe in urine samples.

Metabolism of l-Selenomethionine and Selenite by Probiotic Bacteria: In Vitro and In Vivo Studies

Since selenium supplements have been shown to undergo biotransformation in the gut, probiotic treatment in combination with selenium supplements may change selenium disposition. We investigated the metabolism of L-selenomethionine (SeMet) and selenite by probiotic bacteria in vitro and the disposition of selenium after probiotic treatment followed by oral dosing with SeMet and selenite in rats. When SeMet was incubated anaerobically with individual antibiotic-resistant probiotic strains (Streptococcus salivarius K12, Lactobacillus rhamnosus 67B, Lactobacillus acidophilus L10, and Bifidobacterium lactis LAFTI® B94) at 37°C for 24 h, 11-18% was metabolized with 44-80% of SeMet lost being converted to dimethyldiselenide (DMDSe) and dimethylselenide (DMSe). In similar incubations with selenite, metabolism was more extensive (26-100%) particularly by the lactobacilli with 0-4.8% of selenite lost being converted to DMSe and DMDSe accompanied by the formation of elemental selenium. Four groups of rats (n = 5/group) received a single oral dose of either SeMet or selenite (2 mg selenium/kg) at the time of the last dose of a probiotic mixture or its vehicle (lyoprotectant mixture used to maintain cell viability) administered every 12 h for 3 days. Another three groups of rats (n = 3/group) received a single oral dose of saline or SeMet or selenite at the same dose (untreated rats). Serum selenium concentrations over the subsequent 24 h were not significantly different between probiotic and vehicle treated rats but appeared to be more sustained (SeMet) or higher (selenite) than in the corresponding groups of untreated rats. Probiotic treated rats given SeMet also had selenium concentrations at 24 h that were significantly higher in liver and lower in kidney than untreated rats given SeMet. Thus, treatment with probiotics followed by SeMet significantly affects tissue levels of selenium.

Oxidation mechanisms of dimethyl selenide and selenoxide in the atmosphere initiated by OH radical. A theoretical study

The reaction mechanisms for dimethyl selenide (DMSe) and dimethyl selenoxide (DMSeO) with OH radical are studied by using quantum chemistry calculations. The structures are optimized at MP2 levels, and electronic energies at Gaussian-4 level. Addition complexes are found between reactants as (CH 3) 2Se · OH, (CH 3) 2Se(O) · OH, and (CH 3) 2SeO · HO, which serve as reaction intermediates for further decompositions to CH 3SeOH + CH 3/CH 3SeCH 2 + H 2O, CH 3Se(O)OH + CH 3, and CH 3Se(O)CH 2 + H 2O, respectively. Under the atmospheric conditions, the dominant product channel for DMSe + OH is CH 3SeCH 2 and (CH 3) 2Se · OH, of which the latter is subsequently converted to DMSeO; while the main product for DMSeO + OH is CH 3Se(O)OH. Hydrate formation for DMSeO would not alter the branch ratios because of its small fraction in the atmosphere.

Erratum to: Thin Film Growth of Germanium Selenides from PECVD of GeCl4 and Dimethyl Selenide

In the online published article, it was neglected to note that the flow rates listed in the Table 1 for the DMSe flow were based on a nitrogen flow controller. The nitrogen to DMSe flow rate conversion factor was not available for the MKS flow controller that was used. A conversion factor of 0.34 from a different flow controller manufacturer was recently found. The actual DMSe flow rate may be approximated by multiplying the table entry by 0.34. Thus for a flow rate of 5 sccm listed in the table for DMSe, the true flow rate is likely close to (0.34) 9 5 sccm = 1.7 sccm.

Thin Film Growth of Germanium Selenides from PECVD of GeCl4 and Dimethyl Selenide

Plasma enhanced chemical vapor deposition (PECVD) of germanium selenide thin films from germanium tetrachloride and dimethyl selenide was studied to determine the viability of these reagents for thin film deposition. Germanium tetrachloride and alkylselenides were selected as candidates for these reactions due to their lower toxicities and higher availabilities compared to the more typical substitutes: germane and hydrogen selenide in the formation of germanium selenides. Dimethyl selenide was used successfully for the deposition of germanium selenides. Variation in film stoichiometry was observed by the modification of reactant gas flow ratios. Relative mass flow rates were varied in order to determine their effect on germanium chalcogenide deposition, and the effect of these flow rate modifications on the film thickness, structural properties, and composition are reported.

Combined Speciation Analysis by X-ray Absorption Near-Edge Structure Spectroscopy, Ion Chromatography, and Solid-Phase Microextraction Gas Chromatography−Mass Spectrometry To Evaluate Biotreatment of Concentrated Selenium Wastewaters

In this study we evaluate the potential of anaerobic granular sludge as an inoculum for the bioremediation of selenium-contaminated waters using species-specific analytical methods. Solid species formed by microbial reduction were investigated using X-ray absorption near-edge structure (XANES) spectroscopy at the selenium K-edge. Furthermore, dissolved selenium species were specifically determined by ion chromatography (IC) and solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Least-squares linear combination of the XANES spectra for samples incubated with the highest selenate/selenite concentrations (10(-3) M) show the predominance of elemental selenium and a Se(-I) selenide, such as ferroselite, the thermodynamically most stable iron selenide. In contrast, elemental selenium and Se(-II) selenides are the main species detected at the lower selenate/selenite concentrations. In each repeated fed batch incubation, most aqueous selenite anions were converted into solid selenium species, regardless of the type of electron donor used (acetate or H(2)/CO(2)) and the selenium concentration applied. On the other hand, at higher concentrations of selenate (10(-4) and 10(-3) M), significant amounts of the oxyanion remained unconverted after consecutive incubations. SPME-GC-MS demonstrated selenium alkylation with both electron donors investigated, as dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Selenite was even more alkylated in the presence of H(2)/CO(2) (maximum 2156 μg of Se/L of DMSe + DMDSe) as compared to acetate (maximum 50 μg of Se/L). In contrast, selenate was less alkylated using both electron donors (maximum 166 and 3 μg of Se/L, respectively). The high alkylation potential for selenite limits its bioremediation in selenium laden waters involving H(2)/CO(2) as the electron donor despite the fact that nontoxic elemental selenium and thermodynamically stable metal selenide species are formed.

Headspace hollow fiber protected liquid-phase microextraction combined with gas chromatography–mass spectroscopy for speciation and determination of volatile organic compounds of selenium in environmental and biological samples

A simple and novel speciation method for the determination of volatile organic compounds of selenium (dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) has been developed using a headspace hollow fiber protected liquid-phase microextraction (HS-HF-LPME) combined with capillary gas chromatography–mass spectrometry (GC–MS). The organic solvent impregnated in the pores and filled inside the porous hollow fiber membrane was used as an extraction interface in the HS-HF-LPME of the compounds. The effect of different variables on the extraction efficiency was studied simultaneously using an experimental design. The variables of interest in the HS-HF-LPME were sample volume, extraction time, temperature of sample solution, ionic strength, stirring rate and dwelling time. A Plackett–Burman design was performed for screening in order to determine the significant variables affecting the extraction efficiency. Then, the significant factors were optimized by a Box–Behnken design (BBD) and the response surface equations were derived. Under optimum conditions, preconcentration factors up to 1250 and 1170 were achieved for DMSe and DMDSe respectively. The detection limit and relative standard deviation (RSD) (n=5, c=50μgL−1) for DMSe were 65ngL−1 and 4.8%, respectively. They were also obtained for DMDSe as 57ngL−1 and 3.9%, respectively. The developed technique was found to be applicable to spiked environmental and biological samples.