Voltammetric Studies on Heteropoly Phosphotungstovanadate Anions Across the Liquid／Liquid Interface

Electrochemical transfer behavior of V^vW11--V3^vW9 heteropoly anions on the water/nitrobenzene interface was investigated by means of cyclic voltammetry. The effect of the solution acidity on the transfer behavior and the stable pH range for the heteropoly anions were studied. The stability of mixed tungstovanadate decreases with increasing the number of vanadium atoms. The main transfer species within the potential window have the negative charges of 4 and the transfer process is diffusion-controlled. The apparent transfer potential Δo%wΨ^0 and the free energy ΔGcr^0 w→o for the heteropoly anions can be obtained from the experimental data. For the different anions, the Δo%wΨ1/2pH relationship can be expressed as: Δo%wΨ1/2=constant-53pH.     

Magnetic Solid-Phase Extraction and Ionic Liquid Dispersive Liquid–Liquid Microextraction Coupled with High-Performance Liquid Chromatography for the Determination of Hexachlorophene in Cosmetics

An efficient, simple, and fast method based on ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) followed by magnetic solid-phase extraction (MSPE) was developed as a new technique for extracting and purifying hexachlorophene (HCP) in cosmetics prior to high-performance liquid chromatography (HPLC) determination. In this method based on IL-DLLME and MSPE, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) is used as the extraction solvent and Fe₃O₄ nanoparticles are used to remove hydrophobic additives in the cosmetics by physical adsorption. The main parameters affecting the efficiency of the IL-DLLME and MSPE of HCP were investigated and optimized. Under the optimum conditions, the method was linear in the range 0.5–40 µg mL^?1 with a correlation coefficient (R ²) of 0.9976 and had a detection limit of 0.14 µg mL^?1 at a signal-to-noise ratio (S/N) of 3. The recoveries of HCP in three cosmetic samples using the proposed method were in the range 74.5–97.7%, and the relative standard deviations (RSD, n = 5) were in the range 3.8–6.7%. The developed method was successfully applied to the determination of HCP in cosmetics.     

Liquid–Liquid–Liquid Micro Extraction Combined with CE for the Determination of Rare Earth Elements in Water Samples

A simple method for determination of rare earth elements (REEs) by liquid–liquid–liquid microextraction (LLLME) coupled with capillary electrophoresis and ultraviolet technique was developed. In the LLLME system, 40 mmol L^?1 4-benzoyl-3-methy-1-phenyl-5-pyrazolinone (PMBP) acted as extractant and 4% (v/v) formic acid was used as back-extraction solution. The parameters influencing the LLLME, including the type of the organic solvent, sample pH, formic acid concentration, PMBP concentration, extraction time, volume of organic solvent, stirring rate and phase volume ratio, were investigated. Under the optimized conditions, the detection limits (S/N = 3) of REEs were in the range of 0.19–0.70 ng mL^?1. The developed method was successfully applied to the determination of trace amounts of REEs in water samples.     

Dispersive Liquid–Liquid Microextraction for the Preconcentration of Multiple Classes of Pesticides in Water

A simple, rapid, efficient, and environmentally friendly method was developed for the preconcentration of atrazine, simazine, diuron, bentazone, tebuconazole, and fipronil from water. Dispersive liquid–liquid microextraction was employed with determination by liquid chromatography–tandem mass spectrometry. The volumes of extraction and disperser solvents, the concentration of sodium chloride, and the pH were optimized by response surface methodology. The optimum conditions involved the use of 150 µL of 1:1 (v/v) monochlorobenzene:dichlorobenzene as the extraction solvent, 2 mL acetonitrile as the disperser solvent, and 10 mL of sample at pH 3.0. The accuracy was evaluated in terms of recovery values that were from 54 to 112%. The relative standard deviations ranged from 4 to 27%. The limits of quantification were between 0.005 and 0.05 µg L^?1. The optimized method had low matrix effects for the analytes and the results demonstrated application for the determination of pesticides in water.     

Liquid—Liquid Equilibria for the Water-ethanol-methyl Ethyl Ketone Ternary System at 298.15 and 318.15 K

Abstract

Ternary liquid—liquid equilibrium data for the system water-ethanol-methyl ethyl ketone were obtained at 298.15 and 318.15 K. Data for the binodal curves have been determined by the cloud-point method and conjugate points on tie-lines were determined by gas-chromatographic analysis. Tie-line data at each temperature were satisfactorily correlated by the Othmer and Tobias' method and the plait points coordinates were estimated. The experimental data were also fitted with the UNIFAC group contribution method for the activity coefficients using the isoactivity conditions as restraint equations and with the NRTL and UNIQUAC models.     

Prediction of the Physical Properties for the Ionic Liquid Based on Topological Index

1 INTRODUCTION As a new generation of solvent and catalyst, ionic liquid has captured intensive attention in the field of green chemistry[1, 2]. The most significant physical character is that its property can be changed with different choices of anions, cations and substituents. For example, the water solubility can be altered by choosing proper substituent on cation, and decreased by increasing the length of alkyl chain. On the other hand, critical change of its physical properties can …     

Surface Confined Ionic Liquid—A New Stationary Phase for the Separation of Ephedrines in High-performance Liquid Chromatography

In this article, a new and effective stationary phase based on ionic liquid modified silica is first reported and used for the separation of ephedrines in high-performance liquid chromatography (HPLC). The separation results indicate the high efficiency and reproducibility of the stationary phase. The electrostatic interaction, ion-exchange interaction between the solutes and the stationary phase are considered to attribute the effective separation. Moreover, the free silanols on the surface of the silica are effectively masked by the immobilized ionic liquid, a result of which is to decrease the non-specific absorption.     

Liquid–Liquid Extraction of Organic Compounds into a Single Drop of the Extractant: Overview of Reviews

Single-drop microextraction (SDME) and hollow-fiber membrane microextraction (HFME) belong to methods of the liquid-phase microextraction preconcentration of organic compounds. These methods are characterized by the low consumption of organic solvents, high preconcentration factors, simplicity, low cost, ease of combination with various chromatographic methods; processes of preconcentration and sample injection are combined in a single device. Since the emergence of SDME (1996) and HFME (1999), a large number of versions have been developed that differ in the preconcentration technique, nature of the extractants used, and combinations with methods for the subsequent determination of the preconcentrated substances. The popularity of these methods among the analysts is evidenced by many reviews that we have summarized in this publication.

     

The Effect of Alkane Chain Length on the Liquid–Liquid Critical Temperatures of Oligostyrene/Linear-Alkane Mixtures

Summary. Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N ₁=5) to pentacontane (N ₁=50)) with an oligostyrene (1241amu, N ₂=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains.     

Dispersive Liquid–Liquid Microextraction Combined with Micellar Electrokinetic Chromatography for the Determination of Pesticide in Apple Sample

A fast and reliable dispersive liquid–liquid microextraction method for the determination of three pesticides by micellar electrokinetic chromatography was developed. Several variables that affect the extraction efficiencies, including the type and volume of the extraction solvent and dispersive solvent, extraction time, effect of pH and salt addition, were optimized. Under the optimum conditions, the enrichment factors were obtained in the range of 87 to 95. The extraction recoveries for the target analytes were in the range of 95.0% and 101%, and the relative standard deviation (%) was below 11.3%. The limits of detection at a signal-to-noise ratio of 3 ranged from 50 to 80 ng · mL^?1 with correlation coefficients (r ²) ranging from 0.9958 to 0.9986. The developed method has been successfully applied to the analysis of the three pesticides in apple juice with a satisfactory result.     

The Effect of Alkane Chain Length on the Liquid–Liquid Critical Temperatures of Oligostyrene/Linear-Alkane Mixtures

Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N ₁=5) to pentacontane (N ₁=50)) with an oligostyrene (1241amu, N ₂=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains.     

Dispersive Liquid–Liquid Extraction Based on Freezing of the Organic Drop, Followed by GC for the Determination of Methyl Methacrylate in Wastewater

Crude oil reservoirs typically contain more water than oil, which is emulsified with the oil. During oil production, the emulsion is broken with demulsifiers. Most recently, based on methyl methacrylate, after which, the water, containing the methyl methacrylate, is discharged into surface waters. Significant health hazards have been associated with methyl methacrylate, and a limit of 30 ppm in ground waters has been established. This paper describes the preconcentration of methyl methacrylate from the separated water, using dispersive liquid–liquid microextraction, followed by freezing of the organic drop in an ice bath which facilitated separation of the phases (by centrifugation). In the optimized method, 15.0 μL of 2-dodecanol was rapidly injected into 5 mL water samples, followed by stirring, freezing, and decantation, then direct injection into the gas chromatograph equipped with a flame ionization detector. The method was optimized for: choice of extraction solvent, volume of extraction solvent, pH, ionic strength, temperature and extraction time.     

Excess Molar Volumes and Liquid–Liquid Equilibria of the Ionic Liquid 1-Methyl-3Octyl-Imidazolium Tetrafluoroborate Mixed with Butan-1-ol and Pentan-1-ol

Experimental densities were measured for the system 1-methyl-3-octyl-imidazolium tetrafluoroborate [OMIM][BF₄] + butan-1-ol, + pentan-1-ol at 298.15 K and ambient pressure using a vibrating tube densimeter, taking into account the influence of the viscosity correction. Excess molar volumes V^E have been determined. V^E is quite small and negative in the alcohol-rich range of the mixture composition and positive in the alcohol-poor range. LLE data of [OMIM][BF₄] + pentan-1-ol have been measured using a laser light scattering cell for detecting cloud points at different compositions in the temperature range of 282–292 K. A miscibility gap with an upper critical solution temperature (UCST) of 292 K has been found.     

Low Density Ionic Liquid-Based Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for the Preconcentration of Trace Aromatic Amines in Waters

Journal of Analytical Chemistry - Low density ionic liquid-based ultrasound-assisted dispersive liquid?liquid microextraction for the preconcentration of aromatic amines in river waters and...     

Chemistry of the Positive and Negative Electrical Discharges Formed in Liquid Water and Above a Gas–Liquid Surface

The physical processes and chemical reactions that take place inside different temperature plasma zones in water are only partially understood. The present study uses the emission spectroscopy and hydrogen peroxide measurements as indicators of the processes that take place on the gas–liquid boundary and inside plasma. Based on the hydrogen peroxide measurements with negative and positive high-voltage polarities as a function of solution conductivity, it was concluded that the main difference between positive polarity plasma and negative polarity plasma lies in the active radical concentration inside plasma. Data suggested that in the positive polarity electrical discharge the hydrogen peroxide concentration depends on the solution pH, whereas in the negative polarity discharge, it depends on the solution conductivity. Also, only in the negative polarity discharge do some of the electrons that are emitted from the high voltage electrode diffuse into the bulk where they react with the solutes.     

Improved Homogeneous Liquid–Liquid Extraction Combined with GC–ECD for the Determination of Organochlorinated Pesticides in Water

In this study, improved homogeneous liquid–liquid extraction (HLLE), equipped with GC–ECD has been developed for the extraction and determination of organochlorinated pesticides (OCPs) in water. The phase separation phenomenon occurred by temperature in a ternary solvent (water/methanol/chloroform) system. Several factors influencing the extraction efficiency were investigated and optimized with orthogonal array design. Furthermore, in this study, for the first time, before immiscible organic phase formation, different volumes of deionized water were subjected to homogeneous solution to investigate the effect of this factor on the extraction performance of HLLE. Optimal results were as follows: volume of the extracting solvent (chloroform), 50?μL; volume of the consolute solvent (methanol), 1.2?mL; volume of the sample, 2.5?mL; volume of the deionized water, 0.5?mL; time of centrifuge, 7?min. Under the optimum conditions, repeatability was obtained by spiking OCPs at concentration level of 20?μg?L^?1, the RSDs varied between 4.8 and 10.7% (n?=?4). The limits of detection of 0.02–0.12?μg?L^?1 were obtained for the OCPs. Enrichment factors and the extraction percent of the studied compounds were in the range of 240–300 and 69.2–84.0%, respectively. Finally, the results of the proposed HLLE method were compared with the same HLLE method without addition of deionized water. The results indicated that the proposed method has higher enrichment factors and lower detection limits.     

Application of Solid-Phase Extraction Coupled with Dispersive Liquid–Liquid Microextraction for the Determination of Benzaldehyde in Injectable Formulation Solutions

Solid-phase extraction followed by dispersive liquid–liquid microextraction (SPE-DLLME) technique has been developed as a new analytical approach for extracting, cleaning up and preconcentrating benzaldehyde, a toxic oxidation product of the widely used preservative and co-solvent benzyl alcohol, in injectable formulation solutions. SPE of benzaldehyde from samples was carried out using C₁₈ sorbent. After the elution of benzaldehyde from the sorbent by using acetonitrile, DLLME technique was performed on the obtained solution. Benzaldehyde was preconcentrated by using DLLME technique. Thus, 1.5 mL acetonitrile extract (disperser solvent) and 55.0 µL 1,2-dichloroethane (extraction solvent) were added to 5 mL ultra pure water and a DLLME technique was applied. Several variables that govern the proposed technique were studied and optimized. Under optimum conditions, the method detection limit (LOD) of benzaldehyde calculated as three times the signal-to-noise ratio (S/N) was 0.08 µg L^?1. The relative standard deviation (RSD) for four replicates was 5.8 %. The calibration graph was linear within the concentration range of 0.5–500 µg L^?1 for benzaldehyde. The proposed method has been successfully applied to the analysis of the benzaldehyde in injectable formulation solutions (diclofenac, vitamin B-complex and voltaren) and the relative recoveries were between 88 and 92 % and show that matrix has a negligible effect on the performance of the proposed method.     

Determination of Aristocularine Enantiomers by Dispersive Liquid–Liquid Microextraction and Chiral High-performance Liquid Chromatography

Here is reported a novel analytical approach for the extractive separation and determination of enantiomeric ratios of aristocularine in bovine serum albumin. The results demonstrate suitable analytical performances. The separation was performed by chiral high-performance liquid chromatography with a 5-µm column using a mobile phase of 1:1 n-hexane:ethanol at a flow rate of 0.7?mL?min^?1 with ultraviolet–visible absorption, circular dichroism, and polarimetric detection. The enantiomers were eluted at 13.2 and 15.6?min for (+) and (?)-aristocularine, with a resolution of 1.58 and a separation factor of 1.27. The analytical parameters for the dispersive liquid–liquid microextraction were optimized; under these conditions, the extraction recoveries were from 88.6% to 93.9% for a two-step extraction. The precision, reported as the percent relative standard deviation, had values from 2.9% to 3.2% for 0.5?µg?mL^?1 of analyte for five replicate measurements using ultraviolet–visible absorption and circular dichroism detection. The limits of detection were between 0.05 and 0.08?µg?mL^?1 with enrichment ratios up to a value of 12.     

Liquid—Liquid Equilibrium in Polydisperse Random Copolymer Blends

Continuous thermodynamics is applied to the liquid‐liquid equilibrium in random copolymer blends. Two copolymers are mixed, each consisting of two different monomer units. Hence, up to four monomer units may be present in the system. Both copolymers are characterized by divariate distribution functions with respect to molecular weight (chain length) and chemical composition. The basic relations necessary for phase equilibrium calculations are derived. The influences of both polydispersities and of the different parameters included in the model for the excess Gibbs free energy are discussed by calculating cloud‐point curves and shadow curves. Applications to practical systems are given.