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in chemical analysis workflow is sample pretreatment to extract the analytes before detection. The recent development of dispersive liquid-liquid microextraction (DLLME) has stimulated progress for extracting and preconcentrating trace hydrophobic analytes from aqueous solutions both rapidly and efficiently. [4][5][6] DLLME is based on spontaneous emulsification upon mixing of a water-insoluble extractant, a dispersive solvent, and an analyte aqueous solution. [7,8] The hydrophobic analyte could be rapidly extracted into extractant nanodroplets because of the higher solubility of the analyte in the extractant than in water. The large surface area of nanodroplets enhances the transfer of the analyte from the surrounding solution to the droplets. Relying on the combination of DLLME and various detection techniques, such as inductively coupled plasma optical emission spectrometry or fluorescence spectrometry, trace chemical analysis has been achieved for diverse applications. [9][10][11] However, these existing approaches require significant improvement due to their time-consuming nature, their requirement for specialized equipment in droplet separation and for large volumes of the analyte solution. [12,13] Many studies have focused on concentrating compounds from a single sessile drop evaporation. [14][15][16][17] A common issue comes from the coffee stain effect that leads to uncontrolled deposition of the analyte on the substrate rather than into a focused spot. Although an evaporating drop can shrink isotropically on superhydrophobic surfaces, micro/nanoscale structures on these surfaces can influence solute deposition, in particular at the final stage of evaporation when the drop size becomes comparable with the structures. [18] Supersensitive detection can be achieved for the materials deposited on highly ordered nanostructures on the substrate by using the plasmonic effect. [19] However, these nanostructures are difficult to fabricate for fast and high throughput analysis. Recent work on drop evaporation of ternary liquid mixtures shows advantageous features that may lead to unpinned drop for solute concentrating. [20,21] Selective evaporation of the volatile co-solvent (ethanol) in the mixture leads to oversaturation of oil and consequently spontaneously formation of tiny droplets. This phenomenon of Preconcentration is key for detection from an extremely low concentration solution, but requires separation steps from a large volume of samples using extracting solvents. Here, a simple approach is presented for ultrafast and sensitive microanalysis from a tiny volume of aqueous solutions. In this approach, liquid-liquid nanoextraction in an evaporating thin liquid film on a spinning substrate is coupled with quantitative analysis in one step. The approach is exemplified using a liquid mixture comprising a target compound to be analyzed in water, mixed with extractant oil and co-solvent ethanol. With rapid evaporation of ethanol, nanodroplets of oil form spontaneously in the film. The compounds are highly conce...
in chemical analysis workflow is sample pretreatment to extract the analytes before detection. The recent development of dispersive liquid-liquid microextraction (DLLME) has stimulated progress for extracting and preconcentrating trace hydrophobic analytes from aqueous solutions both rapidly and efficiently. [4][5][6] DLLME is based on spontaneous emulsification upon mixing of a water-insoluble extractant, a dispersive solvent, and an analyte aqueous solution. [7,8] The hydrophobic analyte could be rapidly extracted into extractant nanodroplets because of the higher solubility of the analyte in the extractant than in water. The large surface area of nanodroplets enhances the transfer of the analyte from the surrounding solution to the droplets. Relying on the combination of DLLME and various detection techniques, such as inductively coupled plasma optical emission spectrometry or fluorescence spectrometry, trace chemical analysis has been achieved for diverse applications. [9][10][11] However, these existing approaches require significant improvement due to their time-consuming nature, their requirement for specialized equipment in droplet separation and for large volumes of the analyte solution. [12,13] Many studies have focused on concentrating compounds from a single sessile drop evaporation. [14][15][16][17] A common issue comes from the coffee stain effect that leads to uncontrolled deposition of the analyte on the substrate rather than into a focused spot. Although an evaporating drop can shrink isotropically on superhydrophobic surfaces, micro/nanoscale structures on these surfaces can influence solute deposition, in particular at the final stage of evaporation when the drop size becomes comparable with the structures. [18] Supersensitive detection can be achieved for the materials deposited on highly ordered nanostructures on the substrate by using the plasmonic effect. [19] However, these nanostructures are difficult to fabricate for fast and high throughput analysis. Recent work on drop evaporation of ternary liquid mixtures shows advantageous features that may lead to unpinned drop for solute concentrating. [20,21] Selective evaporation of the volatile co-solvent (ethanol) in the mixture leads to oversaturation of oil and consequently spontaneously formation of tiny droplets. This phenomenon of Preconcentration is key for detection from an extremely low concentration solution, but requires separation steps from a large volume of samples using extracting solvents. Here, a simple approach is presented for ultrafast and sensitive microanalysis from a tiny volume of aqueous solutions. In this approach, liquid-liquid nanoextraction in an evaporating thin liquid film on a spinning substrate is coupled with quantitative analysis in one step. The approach is exemplified using a liquid mixture comprising a target compound to be analyzed in water, mixed with extractant oil and co-solvent ethanol. With rapid evaporation of ethanol, nanodroplets of oil form spontaneously in the film. The compounds are highly conce...
In this work mass transfer enhancement of non‐dispersive solvent extraction by use of helical hollow fiber membranes (HHFM) was investigated by means of experiment and model simulation. Purified terephthalic acid wastewater treatment by extraction with p‐xylene as solvent was chosen as the application case. Experiments showed that extraction efficiency of the HHFM was doubly enhanced compared with that of the straight hollow fiber. A comprehensive mathematical model of the HHFM extraction was developed in an orthogonal helical coordinate system with an analytical solution of the 3D velocities. Model simulation revealed that Dean vortices circulate the peripheral fluid to the center, which enhances the mass transfer in the lumen side where radial diffusion is the rate determining step of the extraction. Relations of effluent impurity concentration and enhancement factor with the Graetz number and dimensionless curvature, were obtained by model simulation. Optimal parameters were selected for HHFM extraction design. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3479–3490, 2017
Dispersive liquid-liquid microextraction (DLLME) coupled with CE was developed for simultaneous determination of five types of chlorophenols (CPs), namely 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) in water samples. Several parameters affecting DLLME and CE conditions were systematically investigated. Under the optimized DLLME-CE conditions, the five CPs were separated completely within 7.5 min and good enrichment factors were obtained of 40, 193, 102, 15, and 107 for 4-CP, 2,4,6-TCP, 2,4-DCP, 2-CP, and 2,6-DCP, respectively. Good linearity was attained in the range of 1-200 μg/L for 2,4,6-TCP, 2,4-DCP, 2-300 μg/L for 4-CP and 2-CP, and 1-300 μg/L for 2,6-DCP, with correlation coefficients (r) over 0.99. The LOD (S/N = 3) and the LOQ (S/N = 10) were 0.31-0.75 μg/L and 1.01-2.43 μg/L, respectively. Recoveries ranging from 60.85 to 112.36% were obtained with tap, lake, and river water spiked at three concentration levels and the RSDs (for n = 3) were 1.31-11.38%. With the characteristics of simplicity, cost-saving, and environmental friendliness, the developed DLLME-CE method proved to be potentially applicable for the rapid, sensitive, and simultaneous determination of trace CPs in complicated water samples.
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