Speciation and Determination of Trace Amount of Inorganic Arsenic in Water,Environmental and Biological Samples

A new speciation and preconcentration method based on dispersive liquid‐liquid microextraction has been developed for trace amounts of As(III) and As(V) in urine and water samples. At pH 4, As(III) is complexed with ammoniumpyrrolidine dithiocarbamate and extracted into 1‐Hexyl‐3‐methylimidazolium hexafluorophosphate, as an ionic liquid (IL) and As(III) is determined by electrothermal atomic absorption spectrometery (ETAAS). Arsenic(V) in the mixing solution containing As(III) and As(V) was reduced by using KI and ascorbic acid in HCl solution and then the procedure was applied to determination of total arsenic. Arsenic(V) was calculated as the difference between the total arsenic content and As(III) content. The effect of various parameters on the recovery of the arsenic ions has been studied. Under the optimum conditions, the enrichment factor 135 was obtained. The proposed method was successfully applied to the determination of trace amounts of As(III) and As(V) in water and biological samples.     

Excess molar volumes of binary mixtures of aliphatic alcohols (C1-C5) with Nitromethane over the temperature range 293.15 to 308.15 K: Application of the ERAS model and cubic EOS

Densities were measured for the binary mixtures of methanol, ethanol, 1-propanol, 1-butanol with nitromethane at temperatures (293.15, 298.15, 303.15 and 308.15) K and for 1-pentanol with nitromethane at temperatures (303.15 and 308.15) K and atmospheric pressure. Densities were determined using a vibrating-tube densimeter. Excess molar volumes as a function of mole fraction were derived, and the computed results were fitted to the Redlich-Kister equation. Excess molar volumes of mixtures studied were consistently described by the ERAS model. Also The Peng-Robinson-Stryjek-Vera (PRSV) equation of state was applied, in combination with simple mixing rules.     

Electrochemical Investigation of Cytochrome c Immobilized onto Self‐Assembled Monolayer of Captopril

The electrochemical behavior of cytochrome c (cyt‐c) that was electrostatically immobilized onto a self‐assembled monolayer (SAM) of captopril (capt) on a gold electrode has been investigated. Cyclic voltammetry, scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy were employed to evaluate the blocking property of the capt SAM. SECM was used to measure the bimolecular electron transfer (ET) kinetics (k_BI) between a solution‐based redox probe and the immobilized protein. In addition, the tunneling ET between the immobilized protein and the underlying gold electrode was calculated. A k_BI value of (5.0±0.6)×10⁸ mol^?1 cm³ s^?1 for the bimolecular ET and a standard tunneling rate constant (k⁰) of 46.4±0.2 s^?1 for the tunneling ET have been obtained.     

Hybrid-Density Functional Theory Study and Natural Bond Orbital Interpretation of the Conformational Behavior of 1,3-Dioxanyl, 1,3-Dithianyl,and 1,3-Diselenanyl Carbanions

Abstract

The effective factors on the conformational properties of 1,3-dioxanyl (1), -dithianyl (2), and -diselenanyl (3) carbanions have been investigated by means of the hybrid-density functional theory (DFT) (B3LYP/6-311+G**)-based method and natural bond orbital (NBO) interpretation. The results obtained showed that the axial conformation (i.e., the axial H atom attached to C₂) of carbanion 1 is more stable than its equatorial conformation. Contrary to the carbanion 1, the equatorial conformations of carbanions 2 and 3 are more stable than their corresponding axial conformations. The instability of the axial conformations of carbanions 1–3 increases from carbanion 1 to carbanion 2 but decreases from carbanion 2 to carbanion 3. The NBO analysis showed that the anomeric effect (AE) associated with the electron delocalization increases from carbanion 1 to carbanion 2, but decreases from carbanion 2 to carbanion 3. The calculated total dipole moment values of the axial conformations of carbanions 1–3 are greater than those of their corresponding equatorial conformations, but the calculated total dipole moment difference values between the axial and equatorial conformations decreases from carbanion 1 to carbanion 3. Consequently, the AE associated with the electron delocalization, but not the total dipole moment changes (i.e., Δμ_ax–eq), thus explaining the total energy differences between the axial and equatorial conformations of carbanions 1–3. The correlations between the AE, dipole moments, ΔG_ax–eq, structural parameters, and conformational behaviors of carbanions 1–3 have been investigated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Polysulfone/Brij‐58 blend nanofiltration membranes: preparation,morphology and performance

In present research, novel asymmetric polysulfone (PSF) membranes with high hydrophilicity and noticeable rejection of arsenic, as one of the major environmental problems, were prepared from PSF/Brij‐58/NMP (1‐methyl‐2‐pyrrolidone) system via immersion precipitation. Pure water was used as gelation media. The variation effect of coagulation bath temperature (CBT) and addition of Brij‐58 on morphology, wettabiliy, pure water permeation flux and rejection of As (III) and As (V), as two dominant states of arsenic in the nature, were studied by scanning electron microscopy, contact angle measuring instrument and experimental setup. The results demonstrated that both hydrophilicity and rejection properties of the prepared membranes were significantly enhanced by small addition of Brij‐58 surfactant in the casting solution along with using the lowest level of CBT. Addition of 4 wt. % of Brij‐58 and using cold coagulation bath resulted in the highest rejection of As (V). Initial increase in Brij‐58 concentration, from 0 wt. % to 2 wt. %, resulted in higher rejection of As (III). However, higher Brij‐58 concentrations than 2 wt. % (increase from 2 wt. % to 6 wt. %) led to lower rejection of As (III). Also, it was found out that addition of Brij‐58 in the casting solution along with increasing the CBT resulted in formation of membranes with high permeability and sub‐layer porosity and thin top layer. Copyright © 2012 John Wiley & Sons, Ltd.     

An extended compromise ratio model with an application to reservoir flood control operation under an interval-valued intuitionistic fuzzy environment

This paper presents a novel multiple attribute group decision-making (MAGDM) model based on the compromise ratio method under an interval-valued intuitionistic fuzzy (IVIF) environment. The compromise ratio method under uncertainty is introduced by a group of experts based on the concept that the chosen alternative should be as close as possible to the IVIF-positive-ideal point and as far away from the IVIF-negative-ideal point as possible concurrently. First, an IVIF-weighted geometric averaging (IVIFWGA) operator is employed to aggregate all individual IVIF-decision matrices provided by a group of experts into a collective IVIF-decision matrix. Two new basic IVIF-operations are introduced to handle the evaluation process. Then, an extended collective index in an IVIF environment is proposed to discriminate among alternatives for the evaluation process in terms of subjective and objective information. Finally, to demonstrate the suitability and applicability of the proposed IVIF-MAGDM model, an application example of reservoir flood control operation is given from the recent literature.     

In‐vitro Aluminum Determination and Preconcentration in Blood of Dialysis Patients Based on Ionic Liquid Dispersive Liquid‐Liquid Biomicroextraction by 2‐Amino‐3‐(1H‐imidazol‐4‐yl)propanoic Acid

In this study, trace amounts of aluminum in serum of dialysis patients were chelated with 2‐Amino‐3‐(1H‐imidazol‐4‐yl)propanoic acid (Histidine) and determined by electro‐thermal atomic absorption spectrometry (ETAAS). A fast and efficient method based on ionic liquid dispersive liquid‐liquid bio‐micro‐extraction (IL‐DLLBME) was developed for the determination of Al cation in human blood serum samples. In this work, a small amount of 1‐Hexyl‐3‐methylimmidazolum hexafluorophosphate ([HMIM] [PF₆]) as an extractant solvent was dissolved in acetone as a dispersant solvent and then the binary solution was rapidly injected by a syringe into the serum containing Al³⁺,Which have already in‐vitro chelated by Histidine amino acid (Al‐His) at pH = 6.5. After separation, the settled IL‐phase was dissolved in ethanol up to 200 μL and 20 μL of samples injected into the ET‐AAS by auto‐sampler. Various parameters have been studied and optimized for 10 mL of sample. Under the optimum conditions, the enrichment factor (EF), limit of detection (LOD) and working range (peak area mode) were obtained 53, 15 ng L^?1 and 0.05‐4.1 μg L^?1 respectively. In vitro Al chelation showed that His can significantly decrease aluminum concentration in serum of dialysis patients. Validation of methodology was confirmed by standard reference material (SRM).     

Optimization of parameters for the alcoholic-assisted dispersive liquid–liquid microextraction of estrogens in water

Extraction and determination of estrogens in water samples were performed using alcoholic-assisted dispersive liquid–liquid microextraction (AA-DLLME) and high-performance liquid chromatography (UV/Vis detection). A Plackett–Burman design and a central composite design were applied to evaluate the AA-DLLME procedure. The effect of six parameters on extraction efficiency was investigated. The factors studied were volume of extraction and dispersive solvents, extraction time, pH, amount of salt and agitation rate. According to Plackett–Burman design results, the effective parameters were volume of extraction solvent and pH. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 220 μL 1-octanol as extraction solvent, 700 μL ethanol as dispersive solvent, pH 6 and 200 μL sample volume. Linearity was observed in the range of 1–500 μg L^?1 for E2 and 0.1–100 μg L^?1 for E1. Limits of detection were 0.1 μg L^?1 for E2 and 0.01 μg L^?1 for E1. The enrichment factors and extraction recoveries were 42.2, 46.4 and 80.4, 86.7, respectively. The relative standard deviations for determination of estrogens in water were in the range of 3.9–7.2 % (n = 3). The developed method was successfully applied for the determination of estrogens in environmental water samples.     

K2Re(NCS)6: A weak ferromagnet

The preparation of the potassium salt of hexathiocyanate Re(IV) as a pure and crystalline solid is described. The crystal structure for [{K(H₂O)₂}₂{Re(NCS)₆}] (P2₁/c, a = 8.29132(8) Å, b = 15.0296(2) Å, c = 8.5249(1) Å, β = 90.885(1)°, V = 1062.21(2) Å³) revealed the formation of a 3-D coordination polymer based on K-S linkages. This organization leads to rather short intermolecular S···S contacts. The magnetic behavior for the compound is characterized by substantial antiferromagnetic interactions (with Curie-Weiss parameters C = 1.93 cm³mol⁻¹ and θ = −171 K) that in turn lead to a weak ferromagnet with T_C = 13 K.     

Nano-structured lead dioxide as a novel stationary phase for solid-phase microextraction

The first study on the high efficiency of nano-structured lead dioxide as a new fiber for solid-phase microextraction (SPME) purposes has been reported. The size of the PbO2 particles was in the range of 34-136 nm. Lead dioxide-based fibers were prepared via electrochemical deposition on a platinum wire. The extraction properties of the fiber to benzene, toluene, ethylbenzene, and xylenes (BTEX) were examined using headspace solid-phase microextraction (HS-SPME) mode coupled to gas chromatography-flame ionization detection (GC-FID). The results obtained proved the suitability of proposed fibers for the sampling of organic compounds from water. The extraction procedure was optimized by selecting the appropriate extraction parameters, including preparation conditions of coating, salt concentration, time and temperature of adsorption and desorption and stirring rate. The calibration graphs were linear in a concentration range of 0.1-100 microg l(-1) (R2 > 0.994) with detection limits below 0.012 microg l(-1) level. Single fiber repeatability and fiber-to-fiber reproducibility were less than 10.0 and 12.5%, respectively. The PbO2 coating was proved to be very stable at relatively high temperatures (up to 300 degrees C) with a high extraction capacity and long lifespan (more than 50 times). Higher chemical resistance and lower cost are among the advantages of PbO2 fibers over commercially available SPME fibers. Good recoveries (81-108%) were obtained when environmental samples were analyzed.