Sharif Digital Repository

A new technique for preparation of an unbreakable solid-phase microextraction (SPME) fiber, using sol-gel technology is developed. Primarily, an ultrathin two-dimensional intermediate film was prepared by hydrolysis of 3-(trimethoxysilyl)-1-propanthiol self-assembled monolayer grafted onto gold, then a stationary phase by electrodeposition of 3-(trimethoxysilyl) propylmethacrylate as a precursor, tetramethyl orthosilicate and polyethylene glycol as a coating polymer was produced. The scanning electron microscopy images revealed that the new fiber exhibits a rather porous and homogenous surface. The thermal stability of the fabricated fiber was investigated by thermogravimetric analysis. The... 

Novel unbreakable solid phase microextraction (SPME) fiber coatings were fabricated by electrospinning method in which the polymeric solution was converted to nanofibers using high voltages. Four different polymers, polyurethane (PU), polycarbonate (PC), polyamide (PA) and polyvinyl chloride (PVC) were prepared as the fiber coatings on thin stainless steel wires. The extraction efficiencies of new coatings were investigated by headspace solid-phase microextraction (HS-SPME) of some environmentally important chlorobenzenes from aqueous samples followed by gas chromatography-mass spectrometry (GC-MS) analysis. Among them, PU showed a prominent efficiency. Effects of coating time and polymer... 

Multivariate curve resolution-alternating least squares (MCR-ALS) as a second-order calibration algorithm was proposed for the simultaneous analysis of eighteen fatty acid methyl esters (FAMEs) in a standard mixture and pomegranate seed sample using vortex-assisted extraction-dispersive liquid-liquid microextraction (VAE-DLLME), followed by gas chromatography-mass spectrometry (GC-MS). The chemometric resolution, identification and quantification of the target FAMEs in the standard mixture and real sample (i.e., the pomegranate seed) were carried out successfully in the presence of some uncalibrated interferences. The lack of fit (LOF) and reverse match factor (RMF) were used for the... 

In this study, organic aerogels were synthesized by the sol-gel polycondensation of mixed cresol with formaldehyde in a slightly basic aqueous solution. Carbon aerogels and xerogels are generated by pyrolysis of organic aerogels. The novel sol-gel-based micro-solid-phase extraction sorbent, resorcinol-formaldehyde xerogel, was employed for preconcentration of some selected herbicides. Three herbicides of the aryloxyphenoxypropionate group, clodinafop-propargyl, haloxyfop-etotyl, and fenoxaprop-P-ethyl, were extracted from aqueous samples by micro-solid-phase extraction and subsequently determined by gas chromatography with mass spectrometry. The effect of different parameters influencing the... 

Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry-selective ion monitoring (GC-MS-SIM) was applied to the determination of methyl tert-butyl ether (MTBE) in water samples. The effect of main parameters affecting the extraction efficiency was studied simultaneously. From selected parameters, volume of extraction solvent, volume of dispersive solvent, and salt concentration were optimized by means of experimental design. The statistical parameters of the derived model were R 2=0.9987 and F=17.83. The optimal conditions were 42.0μL for extraction solvent, 0.30mL for disperser solvent and 5% (w/v) for sodium chloride. The calibration linear range... 

Differential pulse polarography (DPP) was applied for the determination of the herbicide Tribenuron-methyl (TBM). This is a first study for various parameters affecting the reduction peak current were simultaneously optimized using experimental design and these results are different from other reports. The effect of factors such as voltage step, voltage step time, pulse amplitude, pulse time, sample pH, concentration of the supporting electrolyte and the mercury drop size were assessed by means of a (27-2) fractional factorial design. It was found that the effects and interactions of four out of seven factors were significant. Consequently, a central composite design (CCD) with four factors,... 

In this study, a fast and sensitive flow injection μ-solid phase extraction (FI-μ-SPE) technique based on an electrospun polyaniline (PANI) nanocomposite in conjunction with gas chromatography-mass spectrometry (GC-MS) was developed. The PANI-based nanocomposite was synthesized by electrospinning of a solution containing polyvinyl alcohol (PVA)/PANI. The majority of PVA template was subsequently removed from the whole PVA/PANI nanofibers blend by exposing the electrospun nanocomposite to hot water. The homogeneity, porosity and characterization of the electrospun nanofibers were investigated by the scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Due to... 

Superhydrophobic materials have attracted many attentions in recent years while their application in sample preparation remained almost intact. In this project, a rough surface of melamine formaldehyde foam was silanized by chemical deposition of trichloromethylsilane to form a highly porous and superhydrophobic material, presumably a suitable medium for extracting non–polar compounds such as benzene and its methyl derivatives. The prepared sorbent was packed in a needle for the headspace needle–trap microextraction of benzene, toluene, ethylbenzene and xylenes (BTEX). Major parameters associated with the extraction/desorption processes were considered for optimization. Under the optimized... 

A thin film microextraction method using elecrospun magnetic polybutylene terephthalate nanofibers is developed and implemented to isolate some selected triazines. Due to the high mechanical stability of these nanofibers, they are repeatedly used under harsh magnetic stirring and ultrasonic conditions without any damage and structure degradation. The presence of magnetic nanoparticles within the nanofiber structure increases the extraction efficiency while the fibers could be collected by an external magnet. The synthesized nanocomposite showed strong affinity toward the selected analytes. Apart from the concentration of magnetic nanoparticles within the nanocomposite network, the effect of... 

Hydrogen storage/evolution behavior of nafion/NaCl/graphene quantum dot (GQD) mixed matrix as selective hydrogen capacitor (power source) was evaluated in detail through an electrochemical process at two independent potential ranges. For this purpose, a three-electrode system included Pt disk as counter electrode, Ag/AgCl as reference electrode and GQD-based mixed matrix-modified Pt disk as working electrode. For hydrogen storage, the deposition potential and time were evaluated to −1.0 V (vs. Ag/AgCl) and 120 s, respectively under high basic solution generated using NaOH (1.0 M) solution, followed by evolution of hydrogen at +0.8 V (vs. Ag/AgCl) during formation of hydrogen bubbles. The... 

An electro membrane extraction (EME) methodology was utilized to study the isolation of some environmentally important pollutants, such as chlorophenols, from aquatic media based upon the electrokinetic migration process. The analytes were transported by application of an electrical potential difference over a supported liquid membrane (SLM). A driving force of 10 V was applied to extract the analytes through 1-octanol, used as the SLM, into a strongly alkaline solution. The alkaline acceptor solution was subsequently analyzed by high performance liquid chromatography-ultraviolet (HPLC-UV) detection. The parameters influencing electromigration, including volumes and pH of the donor and...