Development of extraction methods for speciation analysis of selenium in aqueous extracts of medicinal plants

Advanced extraction methods have been developed for direct speciation of dissolved inorganic and organic selenium (Se) species in aqueous extracts of medicinal plants (MPs). The inorganic species of Se (SeIV and SeVI) were separated from organic forms by adsorbing inorganic Se on alumina, while the organic Se was not retained. The retained inorganic Se species was eluted with 10 mL 0.2 M HCl. The total inorganic Se species was determined after prereduction of SeVI into SeIV with concentrated HCl. The SeIV in the eluent and total inorganic Se species were then complexed with diethyldithiocarbamate. The resultant complexes were entrapped in the nonionic surfactant Triton X-114. The total Se, organic Se, total inorganic Se, and SeIV species were determined by electrothermal atomic absorption spectrometry with a modifier. The SeVI concentration was obtained by subtracting SeIV from total inorganic Se contents. The main factors affecting the methodologies were investigated in detail. Under the optimized experimental conditions, the LOD for SeIV was 50 microg/L. Among dissolved inorganic and organic Se species in aqueous extracts of MPs, organic Se species were present in the range of 74-84%, SeIV 3.62-7.47%, and SeVI 12.4-18.57% of total Se contents.     

Determination of arsenic in scalp hair samples from exposed subjects using microwave-assisted digestion with and without enrichment based on cloud point extraction by electrothermal atomic absorption spectrometry

A simple and rapid cloud point extraction (CPE) procedure was applied for preconcentration of trace quantities of arsenic (As) in scalp hair samples. The samples were subjected to microwave-assisted digestion in a mixture of nitric acid and hydrogen peroxide (2 + 1, v/v) prior to preconcentration by CPE. The As in digested samples was complexed with ammonium pyrrolidine dithiocarbamate (APDC), and the resultant As-PDC complex was extracted by a nonionic surfactant, octylphenoxypolyethoxyethanol (Triton X-114). After centrifugation, the surfactant-rich phase was diluted with 0.1 M HNO3 in methanol and analyzed by electrothermal atomic absorption spectrometry. The experimental parameters, i.e., amount of APDC, concentration of Triton X-114, equilibrium temperature and time, were optimized. For validation of the proposed method, a certified reference material (CRM) of human hair (BCR 397) was used. No significant difference (P > 0.05) was observed between the experimental results and certified values of the CRM (paired t-test). The LOD and LOQ obtained under the optimal conditions were 0.025 and 0.083 microg/kg, respectively. The developed method was applied for the determination of As in scalp hair samples from male and female subjects of two villages of Khairpur Mir's, Pakistan.     

Characterization of pathogenic bacteria using ionic liquid via single drop microextraction combined with MALDI-TOF MS

The present research was based on the single drop microextraction (SDME) approach using an ionic liquid drop to extract bacteria from aqueous samples for characterization of pathogenic bacteria by MALDI-TOF MS. The SDME of bacteria from aqueous samples was successfully achieved by using platinum nanoparticles mixed in ionic liquid (IL, 1-butyl-3-methylimidazolium hexafluorophosphate) and IL alone as the extraction drops. The IL was used as liquid drops by SDME to obtain protein profiles from bacteria. Significant numbers of biomarker protein peaks of bacteria were identified from target biological samples. The IL also significantly improved the signal reproducibility of spectra using the SDME approach combined with MALDI-TOF MS. Thus, the present technique was successfully applied to detect pathogenic bacteria at low concentrations of 10(6) cfu mL(-1) from aqueous suspensions. The selected bacteria viz., Escherichia coli and Serratia marcescens were used as target biological sample.     

Dual-band tunable negative refractive index metamaterial with F-Shape structure

This paper presents a negative refractive index tunable metamaterial based on F-Shape structure which is capable of achieving dual-band negative permeability and permittivity, thus dual-band negative refractive index. An electromagnetic simulation was performed and effective media parameters were retrieved. Numerical investigations show clear existence of two frequency bands in which permeability and permittivity both are negative. The two negative refractive index bandwidths are from 23.8 GHz to 24.1 GHz and from 28.3 GHz to 34.9 GHz, respectively. The geometry of the structure is simple so it can easily be fabricated. The proposed structure can be used in multiband and broad band devices, as the band range in second negative refractive index region is 7 GHz, for potential applications instead of using complex geometric structures and easily tuned by varying the separation between the horizontal wires.     

Development of a new green non-dispersive ionic liquid microextraction method in a narrow glass column for determination of cadmium prior to couple with graphite furnace atomic absorption spectrometry

Easy and innovative non-dispersive ionic liquid based microextraction (NDILME) has been developed for preconcentration of trace level of cadmium (Cd) in aqueous real surface water samples prior to couple with graphite furnace atomic absorption spectrometry (GFAAS). A 200 cm long narrow glass column containing aqueous solution of standard/sample was used to increase phase transfer ratio by providing more contact area between two medium (aqueous and extractive), which drastically improve the recoveries of labile hydrophobic chelate of Cd ammonium pyrrolidinedithiocarbamate (APDC), into ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆]. Different aspect of the desire method have been investigated and optimized. Under the optimized key experimental variables, limit of detection (LOD) and enhancement factor (EF) were achieved to be 0.5 ng L⁻¹ and 150, respectively. Reliability of the model method was checked by relative standard deviation (%RSD), which was found to be < 5%. Validity and accuracy of the developed method was checked by analysis of certified reference water samples (SLRS-4 Riverine water) using standard addition method.     

Optical Characterization of rf-Magnetron Sputtered Nanostructured SnO2 Thin Films

Tin oxide （Sn02 ） thin films are deposited by rf-magnetron sputtering and annealed at various temperatures in the range of 100-500 ℃ for 15 min. Raman spectra of the annealed films depict the formation of a small amount of SnO phase in the tetragonal Sn02 matrix, which is verified by x-ray diffraction. The average particle size is found to be about 20-30 nm, as calculated from x-ray peak broadening and SEM images. Various optical parameters such as optical band gap energy, refractive index, optical conductivity, carrier mobility, carrier concentration etc. are determined from the optical transmittance and reflectance data recorded in the wavelength range 250-2500 nm. The results are analyzed and compared with the data in the literature.     

A note on quantization in rotating co-ordinates

The quantization of scalar fields in a uniformly rotating frame is reconsidered. It is pointed out that the coordinates usually used do not represent a frame describing uniform circular motion and the metric in the correct coordinates has a singularity. The result obtained earlier with the wrong coordinates, that there is no radiation, nevertheless holds.

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Zusammenfassung Die Quantisierung skalarer Felder in einem gleichförmig rotierenden Koordinatensystem wird erneut betrachtet. Dabei wird hervorgehoben, daß die gewöhnlich verwendeten Koordinaten die gleichförmige Kreisbewegung nicht beschreiben und daß die Metrik in den richtigen Koordinaten eine Singularität aufweist. Trotzdem bleibt das früher mit den falschen Koordinaten abgeleitete Resultat erhalten, daß nämlich ein strahlungsfreier Zustand existiert.

     

A cooperative mobile throwbox-based routing protocol for social-aware delay tolerant networks

Wireless Networks - In delay tolerant networks (DTNs), nodes have intermittent connectivity patterns due to various factors such as mobility, sparse network topology, and unpredictable movement...     

Perovskite Single Crystals: Synthesis,Properties, and Applications

Perovskite single crystals have gained enormous attention in recent years due to their facile synthesis and excellent optoelectronic properties including the long carrier diffusion length, high carrier mobility, low trap density, and tunable absorption edge ranging from ultra-violet (UV) to near-infrared (NIR), which offer potential for applications in solar cells, photodetectors (PDs), lasers, etc. In this review, we summarized the synthesis, properties, and applications of organic-inorganic mixed and all-inorganic perovskite single crystals, particularly those through the solution synthesis approach. Challenges towards the crystal growth and stability with future perspectives were also briefly described at the end of this paper.