Determination of dimethylselenide and dimethyldiselenide by gas chromatography–photoionization detection

Nanomembrane Canister Architectures for the Visualization and Filtration of Oxyanion Toxins with One-Step Processing

Nanomembrane canister-like architectures were fabricated by using hexagonal mesocylinder-shaped aluminosilica nanotubes (MNTs)-porous anodic alumina (PAA) hybrid nanochannels. The engineering pattern of the MNTs inside a 60 μm-long membrane channel enabled the creation of unique canister-like channel necks and cavities. The open-tubular canister architecture design provides controllable, reproducible, and one-step processing patterns of visual detection and rejection/permeation of oxyanion toxins such as selenite (SeO3(2-)) in aquatic environments (i.e., in ground and river water sources) in the Ibaraki Prefecture of Japan. The decoration of organic ligand moieties such as omega chrome black blue (OCG) into inorganic Al2O3@tubular SiO2/Al2O3 canister membrane channel cavities led to the fabrication of an optical nanomembrane sensor (ONS). The OCG ligand was not leached from the canister as observed in washing, sensing, and recovery assays of selenite anions in solution, which enabled its multiple reuse. The ONS makes a variety of alternate processing analyses of selective quantification, visual detection, rejection/permeation, and recovery of toxic selenite quick and simple without using complex instrumentation. Under optimal conditions, the ONS canister exhibited a high selectivity toward selenite anions relative to other ions and a low-level detection limit of 0.0093 μM. Real analytical data showed that approximately 96% of SeO3(2-) anions can be recovered from aquatic and wastewater samples. The ONS canister holds potential for field recovery applications of toxic selenite anions from water.

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=50 μg L(-1)) for DMSe were 65 ng L(-1) and 4.8%, respectively. They were also obtained for DMDSe as 57 ng L(-1) and 3.9%, respectively. The developed technique was found to be applicable to spiked environmental and biological samples.

Comparison of two derivatizing agents for the simultaneous determination of selenite and organoselenium species by gas chromatography and atomic emission detection after preconcentration using solid-phase microextraction

Two methods for the simultaneous determination of selenite and two organoselenium compounds, dimethylselenide (DMSe) and dimethyldiselenide (DMDSe), are proposed. Both methods involve sample preconcentration by solid-phase microextraction (SPME) and capillary gas chromatography coupled to atomic emission detection (GC-AED). The main difference between the methods is the derivatizing agent used to complex the inorganic species: sodium tetraethylborate and 4,5-dichloro-1,2-phenylenediamine. The parameters affecting the derivatization and preconcentration steps, chromatographic separation as well as detection of the compounds were optimized. Direct immersion (DI) mode and a relatively long extraction time were selected for the method involving the formation of the piazselenol complex, better sensitivity being achieved for the three analytes under study. In this case, detection limits ranged between 3 and 25 ng L(-1), depending on the compound. Headspace mode (HS) and extraction times of 20 min were selected for the method involving tetraalkylborate, and detection limits of between 7.3 and 55 ng L(-1) were obtained. DMSe and Se(IV) were found in several of the water samples analyzed at concentrations of 0.07-1.0 ng mL(-1).

Reduction of selenite to elemental red selenium by Rhizobium sp. strain B1

A bacterium that reduces the soluble and toxic selenite anion to insoluble elemental red selenium (Se(0)) was isolated from a laboratory bioreactor. Biochemical, morphological, and 16S rRNA gene sequence alignment identified the isolate as a Rhizobium sp. that is related to but is genetically divergent from R. radiobacter (syn. Agrobacterium tumefaciens) or R. rubi (syn. A. rubi). The isolate was capable of denitrification and reduced selenite to Se(0) under aerobic and denitrifying conditions. It did not reduce selenate and did not use selenite or selenate as terminal e(-) donors. Native gel electrophoresis revealed two bands, corresponding to molecular weights of approximately 100 and approximately 45 kDa, that reduced selenite. Tungsten inhibited in vivo selenite reduction, suggesting that a molybdenum-containing protein is involved in selenite reduction. This organism, or its enzymes or DNA, might be useful in bioreactors designed to remove selenite from water.

Halitosis associated volatiles in breath of healthy subjects

BACKGROUND

Halitosis can have an intra- or extra-oral origin. In all cases, bad breath is caused by the presence of volatile organic compounds originating from the mouth or the expired air. They can be specific for certain diseases or infections.

STUDY OBJECTIVE

This study explored the presence and concentration of these volatile compounds normally associated with halitosis in the breath of healthy symptomless volunteers.

METHODS

Alveolar and mouth air of 40 healthy volunteers as well as environmental air were analyzed by gas chromatography-mass spectrometry (GC-MS) and by a commercially available GC device (OralChroma).

RESULTS

14 compounds, associated with halitosis could be detected. All of them except carbon disulfide, appeared to be (partly) produced endogenously and/or in the mouth. Acetone, 2-butanone, 2-pentanone and 1-propanol were common to all volunteers in both alveolar and mouth air and indole and dimethyl selenide in alveolar air.

CONCLUSIONS

GC-MS seems a promising tool for differential diagnosis of halitosis, with the possibility to detect extra-oral causes, which often remain undetected unless characterized by a specific smell.

An Azospira oryzae (syn Dechlorosoma suillum) strain that reduces selenate and selenite to elemental red selenium

A bacterium that reduces the soluble selenium oxyanions, selenate and selenite, to insoluble elemental red selenium (Se(0)) was isolated from a laboratory reactor developed to remove selenate from groundwater. Gene sequence alignment of the 16S rRNA allowed identification of the isolate as Azospira oryzae. Biochemical and morphologic characterization confirm the identification. The isolate reduces selenate and selenite to Se(0) under microaerophilic and denitrifying conditions but not under aerobic conditions. It does not use selenate or selenite as terminal e(-) donors. Se oxyanion reduction causes the formation of Se nanospheres that are 0.25 +/- 0.04 microm in diameter. Nanospheres may be associated with the cells or free in the medium. The enzymatic activity associated with the reduction of selenate has a molecular mass of approximately 500 kD, and the enzymatic activity associated with the reduction of selenite has a mass of approximately 55 kD. Selenite reduction was inhibited by tungsten. The molecular masses of these activities were different from those associated with the reduction of dimethylsulfoxide, sulfate, and nitrite. This bacterium, or perhaps its enzymes or DNA, might be useful for the remediation of waters contaminated with Se oxyanions.

Identification and characterization of an Aeromonas salmonicida (syn Haemophilus piscium) strain that reduces selenite to elemental red selenium

A bacterium that reduces toxic and mobile selenite to insoluble elemental selenium (Se0) was isolated from a laboratory scale permeable reactive biobarrier. Biochemical tests and 16S rRNA gene sequence alignment identified the isolate as Aeromonas salmonicida. Two colony types were isolated, one more resistant to selenite than the other. Both grew on agar plates containing 16 mM: selenite, although the colony diameter was reduced to 8% of controls with the small colony type and to 18% with the large colony type. Further study was done with the large colony type. In anaerobic culture, this bacterium was able to use nitrate as a term electron acceptor but not selenate or selenite. In aerobic culture, when no nitrate was present, early log phase cells removed selenite at a rate of 2.6 +/- 0.42 micromol SeO3 (-2)/mg protein/day. Reduction was retarded by 25 mM: nitrate. Mutants with a diminished ability to reduce selenite to Se0 also had a reduced ability to reduce nitrate to nitrous oxide. This bacterium, or perhaps its enzymes or DNA, might be used to remove selenite from contaminated groundwaters.

Gas chromatography with atomic emission detection for dimethylselenide and dimethyldiselenide determination in waters and plant materials using a purge-and-trap preconcentration system

Dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) were determined in plant and water samples by capillary gas chromatography using microwave induced-plasma atomic emission spectrometry for detection. The analytes were leached from the solid samples into methanol by using an ultrasonic probe, and a portion of the extract was preconcentrated by means of a purge-and-trap system before being chromatographed. The analytes were directly purged from the water samples in the presence of 6% (v/v) methanol. Element-specific detection and quantification was carried out by monitoring the selenium (196 nm) emission line. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were 0.9999 for both analytes. Detection limits of 0.8 and 1.1 ng l(-1) were obtained for DMSe and DMDSe, respectively, for water samples. For plant materials, the detection limits calculated for 0.5 g samples were 0.3 and 0.4 ng g(-1) for DMSe and DMDSe, respectively. Concentration levels of DMSe ranging from 1.2 to 4.2 ng g(-1) were found in some of the plant materials analyzed. No DMDSe was found in any of the samples. The accuracy of the method was checked by analyzing different spiked water and plant samples.

Removing selenite from groundwater with an in situ biobarrier: laboratory studies

Laboratory biobarriers were evaluated for their ability to remove selenite from flowing groundwater. Microbial activity in aquifers is usually limited by substrate availability, and biobarriers stimulate microbial activity by providing a substrate; for these studies soybean oil was used. Water containing 10 mg L(-1) selenite-Se was pumped through the biobarriers for 74 days and the amount present in the effluent monitored. The amounts remained high for the first 2 weeks of the study but then declined. From day 28 until the end of the study the amount of selenite-Se in the column effluents averaged 0.20 +/- 0.04 mg L(-1), a decrease of approximately 98%. At the end of the study about half of the selenite-Se applied to the columns was recovered as immobilized selenium trapped by the biobarrier. This study suggests that biobarriers containing vegetable oil might be used as a process for removing selenite from contaminated groundwater.