Single-walled carbon nanotubes as solid-phase microextraction adsorbent for the determination of low-level concentrations of butyltin compounds in seawater

Carbon nanotubes are a kind of new carbon-based nanomaterials, which have drawn great attention in many application fields. The potential of single-walled carbon nanotubes (SWCNTs) as solid-phase microextraction (SPME) adsorbent for the preconcentration of environmental pollutants has been investigated in recent years. In the present study, the feasibility of SWCNTs as SPME adsorbent for the determination of monobutyltin, dibutyltin and tributyltin in seawater samples was studied. To achieve this aim, the potential factors affecting the SPME efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance according to the ICH (International Conference on Harmonization of Technical Requirements for Analytical Methods) criteria. The acquired calibration curves were linear (r ≥ 0.992) over the concentration range from ≤12 to 2000 ng L⁻¹. For all of the analytes, the limit of detection at signal-to-noise ratio of 3 was below 5 ng L⁻¹. Furthermore, in comparison with the commercial carboxen/polydimethylsiloxane fiber, the developed SWCNT fiber showed better thermal stability (over 350 °C) and longer life span (over 150 times). The application of the proposed method in environmental analyses was shown by analyzing seawater samples from the harbors on the Persian Gulf for butyltin residues. Some of the butyltins were detected in the analyzed samples. Results of the present study demonstrate the feasibility of the SWCNTs as SPME adsorbent for the determination of butyltins in seawater samples.     

Specifications of dust-ion-acoustic shock waves affected by dust charge variation in four-component dissipative quantum plasma

ABSTRACT

Nonlinear propagation of dust-ion-acoustic shock waves in an unmagnetized, collisionless four-component quantum plasma containing electrons, positrons, ions and negatively charged dust grains affected by dust charge variations and viscosity of ions is studied using quantum hydrodynamic model. Considering dust charge variation give rise to calculating of charging currents of the plasma particles. These currents have been calculated with orbit limited motion theory and using Fermi-distribution functions or Boltzmann–Maxwell distribution depending on quantum or classical particles, respectively. The basic characteristics of quantum dust-ion-acoustic shock waves are investigated by deriving Korteweg–de Vries–Burgers equation under the reductive perturbation method. Depending on the relative values of the dispersive and dissipative coefficients, oscillatory and monotonic shock waves can propagate in the plasma model. The effect of chemical potential and density of dust particles on the shock wave’s height and thickness is investigated. In addition, the critical value of H (H_c) is calculated and it is shown that for R?>?0 compressive shock waves and for R?<?0 rarefactive ones can exist. The present study is applicable to researchers on quantum nonlinear structures in dense astrophysical objects and ultra-small micro- and nano-electronic devices.     

Shape control of nanostructured TiO2 using a Schiff base ligand via sol–gel hydrothermal method

Employing a Schiff base ligand in a hydrothermal sol–gel method for preparation of TiO₂ nanostructures was studied. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrum, electron dispersive X-ray spectroscopy and ultraviolet–visible spectroscopy. It is shown that in the controlled reaction conditions, a Schiff base ligand containing hard atoms is capable of driving the growth mechanism in a way that anisotropic shapes of TiO₂ nanostructures are formed. Considering the structure of the Schiff base ligand, the possible growth mechanism of TiO₂ nanostructures is proposed. The optical studied as well as calculated molecular orbital structure of ligand by density functional theory is done.     

Sorptive thin film microextraction followed by direct solid state spectrofluorimetry: A simple,rapid and sensitive method for determination of carvedilol in human plasma

A poly acrylate-ethylene glycol (PA-EG) thin film is introduced for the first time as a novel polar sorbent for sorptive extraction method coupled directly to solid-state spectrofluorimetry without the necessity of a desorption step. The structure, polarity, fluorescence property and extraction performance of the developed thin film were investigated systematically. Carvedilol was used as the model analyte to evaluate the proposed method. The entire procedure involved one-step extraction of carvedilol from plasma using PA-EG thin film sorptive phase without protein precipitation. Extraction variables were studied in order to establish the best experimental conditions. Optimum extraction conditions were the followings: stirring speed of 1000 rpm, pH of 6.8, extraction temperature of 60 °C, and extraction time of 60 min. Under optimal conditions, extraction of carvedilol was carried out in spiked human plasma; and the linear range of calibration curve was 15–300 ng mL⁻¹ with regression coefficient of 0.998. Limit of detection (LOD) for the method was 4.5 ng mL⁻¹. The intra- and inter-day accuracy and precision of the proposed method were evaluated in plasma sample spiked with three concentration levels of carvedilol; yielding a recovery of 91–112% and relative standard deviation of less than 8%, respectively. The established procedure was successfully applied for quantification of carvedilol in plasma sample of a volunteer patient. The developed PA-EG thin film sorptive phase followed by solid-state spectrofluorimetric method provides a simple, rapid and sensitive approach for the analysis of carvedilol in human plasma.     

Synthesis of gold nanoparticles decorated on sulfonated three‐dimensional graphene nanocomposite and application as a highly efficient and recyclable heterogeneous catalyst for Ullmann homocoupling of aryl iodides and reduction of p‐nitrophenol

Gold nanoparticles were decorated onto sulfonated three‐dimensional graphene (3DG‐SO₃H) through spontaneous chemical reduction of HAuCl₄ by 3DG‐SO₃H. This nanocomposite exhibited excellent catalytic activity for the synthesis of symmetric biaryls via the Ullmann homocoupling of aryl iodides in an aqueous medium. Additionally, this nanocomposite was used as a catalyst for the reduction of p‐nitrophenol to p‐aminophenol. The catalyst could be used more than six times successively without significant deactivation.     

A novel,chemoselective one-pot procedure for the preparation of 3H-spiro[isobenzofuran-1,2′-pyrrole]-3,3′(1′H)-dione derivatives via oxidative cleavage of 3a,8b-dihydroxyindeno[1,2-b]pyrroles

A one-pot, efficient and chemoselective procedure for the synthesis of new 3H-spiro[isobenzofuran-1,2′-pyrrole]-3,3′(1′H)-dione derivatives has been developed which involves room temperature oxidative cleavage of 3a,8b-dihydroxyindeno[1,2-b]pyrroles themselves synthesized from the reaction of ninhydrin and enaminones in 30% ethanol. A reasonable mechanism is proposed for the oxidation reaction based on the results of this study and our previous related work.     

Photovoltaic spatial soliton pairs in two-photon photorefractive materials

We report the existence of incoherently coupled bright-bright steady state photovoltaic soliton pairs in two-photon photorefractive material under open circuit conditions. Based on WKBJ method and paraxial ray approximation, we have obtained coupled equations describing dynamical evolution of spatial soliton pairs. In the steady state regime, the present analysis leads to the identification of existence equation of bright-bright solitons, which captures a plethora of soliton pairs. We have undertaken linear stability analysis which shows that these solitons are stable.     

A high-throughput approach for the determination of pesticide residues in cucumber samples using solid-phase microextraction on 96-well plate

A high-throughput solid-phase microextraction (SPME) on 96-well plate together with gas chromatography–mass spectrometry (GC–MS) was developed for the determination of some selected pesticides in cucumber samples. Pieces with the length of 1.0 cm of silicon tubing were precisely prepared and then coated on the end part of stainless steel wires. The prepared fibers were positioned in a home-made polytetrafluoroethylene (PTFE)-based constructed ninety-six holes block to have the possibility of simultaneous immersion of the SPME fibers into the center of individual wells. Pesticides such as diazinon, penconazol, tebuconazol, bitertanol, malathion, phosalone and chlorpyrifos-methyl were selected for their highly application in cucumber field. The performances of the SPME fibers, such as intra and inter-fibers reproducibility, were evaluated and the results showed a good similarity in extraction yields. A volume of 1 mL of the aquatic supernatant of the cucumber samples was transferred into the 96-well plate and the array of SPME fibers was applied for the extraction of the selected pesticides. The important parameters influencing the whole extraction process including, organic solvent percent, salt addition, dilution factor, stirring rate and extraction time were optimized. The inter- and intra-day RSD% were found to be less than 15.4%. Limits of detection (LOD) and limits of quantification (LOQ) were below 60 and 180 μg kg⁻¹, respectively. The coefficient of determination was satisfactory (r² > 0.99) for all the studied analytes. The developed method was successfully applied to the monitoring of several samples gathered from local markets.