Application of headspace solvent microextraction to the analysis of mononitrotoluenes in waste water samples

The possibility of applying headspace solvent microextraction (HSME) for determination of mononitrotoluenes (MNTs) in waste water samples is demonstrated. A drop of n-amyl alcohol containing naphthalene as an internal standard was suspended from the tip of a microsyringe needle over the headspace of stirred sample solutions for a predescribed extraction period. The drop was then injected directly into a gas chromatograph. Optimization of experimental parameters such as the nature of extracting solvent, microdrop and sample volumes, sampling temperature, stirring rate, ionic strength of the solution, pH and extraction time on HSME efficiency were investigated. Then enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by water samples spiked with MNTs. Finally, the method was successfully applied to the extraction and determination of the mononitrotoluenes in waste waters of both P.C.I. Company and Research Center of Azad University.     

Novel modified carbon nanotubes as a selective sorbent for preconcentration and determination of trace copper ions in fruit samples

In this work, multiwalled carbon nanotubes were reacted with N‐[3‐(triet‐hoxysilyl)propyl]isonicotinamide to prepare pyridine‐functionalized carbon nanotubes. This novel sorbent was characterized by infrared spectroscopy, thermal and elemental analysis, and scanning electron microscopy. Functionalized carbon nanotubes were applied for the preconcentration and determination of copper ions using flame atomic absorption spectrometry. Various parameters such as sample pH, flow rate, eluent type and concentration, and its volume were optimized. Under optimal experimental conditions, the limit of detection, the relative standard deviation, and the recovery of the method were 0.65 ng/mL, 3.2% and 99.4%, respectively. After validating the method using standard reference materials, the new sorbent was applied for the extraction and determination of trace copper(II) ions in fruit samples.     

Optimization of a novel method based on solidification of floating organic droplet by high-performance liquid chromatography for evaluation of antifungal drugs in biological samples

In this study, a simple, rapid, and highly efficient liquid-phase microextraction method based on solidification of floating organic droplet was coupled with high performance liquid chromatography-photo diode array detection (HPLC-PDA) for determination of ketoconazole, clotrimazole, and miconazole as antifungal drugs. Central composite design (CCD) was used for optimization of several factors affecting the extraction efficiency. The optimized conditions were established to be 550 rpm for stirring rate, 35 min for extraction time, 57 °C for extraction temperature, 8.5 for solution pH, 10 μl for organic solvent volume, and 7% (w/v) of NaCl for ionic strength. Limit of detections (LODs) of the extraction method ranged from 0.01 to 0.1 μg L⁻¹ and the linear dynamic ranges (LDRs) ranged from 0.1 to 300 μg L⁻¹ for the three antifungal drugs. Relative standard deviations (RSDs) of the proposed method were 5-11%. Preconcentration factors in the range of 306-1350 were obtained at extraction time of 35 min. Finally, performance of the proposed method was evaluated for the extraction and determination of the drugs’ levels in microgram per liter in samples and satisfactory results were obtained.     

A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g⁻¹. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L⁻¹, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples.

A schematic procedure of magnetic solid phase extraction

     

A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g^?1. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L^?1, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples. Figure

A schematic procedure of magnetic solid phase extraction     

Optimization of carrier-mediated three-phase hollow fiber microextraction combined with HPLC-UV for determination of propylthiouracil in biological samples

Carrier-mediated three-phase hollow fiber microextraction combined with high-performance liquid chromatography-ultra violet detection (HPLC-UV) was applied for the extraction and determination of propylthiouracil in biological samples. Propylthiouracil (PTU) was extracted from 7.5 mL of the basic solution (the source phase) with pH 12 into an organic phase (n-octanol containing 6% (w/v) of Aliquat 336 as the carrier) impregnated in the pores of a hollow fiber, and finally was back extracted into 24 μL of the acidic solution located inside the lumen of the hollow fiber (the receiving phase). The extraction was performed through the gradient of counter ion from the source to the receiving phase. The effects of different variables on the extraction efficiency were studied simultaneously using an experimental design. A half-fractional factorial design was employed for screening to determine the variables significantly affecting the extraction efficiency. Then, the factors with significant effect were optimized using a central composite design (CCD) and the response surface equations were developed. The optimal experimental conditions obtained from this statistical evaluation included: source phase, pH 12; temperature, 25 °C; extraction time, 40 min; counter ion concentration, 2 mol L⁻¹ of NaClO₄; organic solvent 6% of Aliquat in octanol and without salt addition in the source phase. Under the optimized conditions, the preconcentration factors were between 125 and 198 and also the limit of detections (LODs) ranged from 0.1 μg L⁻¹ to 0.4 μg L⁻¹ in different biological samples. The calibration curve was linear (r² = 0.998) in the concentration range of 0.5-1000 μg L⁻¹. Finally, the feasibility of the proposed method was successfully confirmed by extraction and determination of PTU in human plasma and urine as well as the bovine milk and meat samples in microgram per liter, and suitable results were obtained (RSDs < 6.3%).     

Homogeneous liquid-liquid extraction of trace amounts of mononitrotoluenes from waste water samples

Homogeneous liquid-liquid extraction method was studied based on a phase separation phenomenon in a ternary solvent system. According to this procedure, mononitrotoloenes were extracted by single-phase extraction in a water/methanol/chloroform, homogeneous ternary solvent system. Methanol and chloroform were used as consolute and extraction solvents, respectively. The homogeneous solution was broken by the addition of salt and a cloudy solution was formed. After centrifugation, the fine droplets of the extraction solvent were sedimented in the bottom of the conical test tube. Analysis of the extracts was carried out by gas chromatography. The optimization procedure was performed using Box-Behnken design. The variables involved were: sample and extraction solvent volumes, consolute solvent volume and phase separator reagent concentration. Optimum results were obtained under the following conditions: sample volume of 5 mL, extraction solvent volume of 55 μL, consolute solvent volume of 1 mL and phase separator reagent concentration; 5% (w/v). Under these conditions, the enrichment factors of 354, 311 and 300, dynamic linear ranges of 0.5-500, 1-500 and 1-500 μg L⁻¹, and limit of detections (LODs) of 0.09, 0.09 and 0.1 μg L⁻¹ were obtained for o-nitrotoluene, m-nitrotoluene and p-nitrotoluene, respectively. Finally, the method was successfully applied to the extraction and determination of MNTs in the waste water samples in the range of micrograms per liter with R.S.Ds. < 13.2%.     

Investigation of stresses and normal stress differences behavior on symmetric and asymmetric polymeric fluid flow through planar gradual expansions

A numerical study of stress distribution of polymeric viscoelastic fluids passing through planar gradual expansion channels is conducted. To model the viscoelastic behavior in geometries with 1:3 expansion ratios, the exponential form of Phan-Thien Tanner model is employed as the constitutive equation. The PISO algorithm is used to solve the flow field distribution. Three different expansion angles of 30°, 45° and 60° are considered to probe the effects of the gradual expansion and its effect on the stress field distribution. The main purpose of the current study is to analysis the combined effects of the rheological properties and inertia on the normal stress distribution. To achieve this aim, different expansion angles and different ranges of Weissenberg and Reynolds numbers are studied.