Search

A simple, fast, effective, and environmentally friendly method, in situ solvent formation microextraction combined with magnetic dispersive micro-solid-phase extraction for the determination of four benzoylurea insecticides is presented herein for the first time. In the proposed method, 1-hexyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]imide was formed by the reaction between 1-hexyl-3-methylimidazolium chloride and lithium bis[(trifluoromethane)sulfonyl]imide and was used to extract benzoylurea insecticides. Then magnetic nanoparticles were added as carrier to retrieve and separate the ionic liquid from the sample solution. After the supernatant was removed, the ionic liquid was desorbed using acetonitrile and subsequently injected directly into a high-performance liquid chromatograph equipped with a variable wavelength detector for analysis. The main factors affecting the extraction efficiency were investigated by a one factor at a time approach. Under optimized conditions, the proposed method showed good repeatability (RSD = 2.2-4.5%) and linearity (2-300 μg/L), with correlation coefficients greater than 0.9994 and low limits of detection (0.67-1.46 μg/L). Finally, the method was successfully applied to the analysis of four benzoylurea insecticides in environmental water samples with good recoveries (73.2-85.8%).

A novel in-syringe dispersive liquid-liquid microextraction based on the solidification of ionic liquids (in-syringe SIL-DLLME) was coupled with high-performance liquid chromatography-ultraviolet detector (HPLC-UVD) to detect five benzoylurea insecticides (BUs) in water and tea beverage samples. In this method, the hydrophobic ionic liquid [N8881][PF6] was formed in situ by the metathesis reaction between [N8881]Cl and the anion-exchange reagent KPF6 to extract the target analytes. The whole extraction procedure was performed in a syringe. The solidified extractant could be separated from the aqueous phase by exposing the emulsified extraction solution to an ice bath and then easily collected by squeezing out the aqueous phase through the prepared NWPP-based needle. Various parameters affecting the extraction efficiency, such as the amount of [N8881]Cl, the molar ratio of [N8881]Cl to KPF6, salt addition, cooling time, solution temperature, sample pH and sample volume, were evaluated. Under the optimized conditions, the proposed method was validated with satisfactory results: good linearities with coefficients of determination greater than 0.99 were obtained in the range of 2-500µgL-1; the limits of detection varied between 0.29 and 0.59µgL-1; the recoveries of the five benzoylurea insecticides ranged from 85.93% to 90.52%; and the intra-day (n=3) and inter-day (n=3) relative standard deviations were less than 5.36%. Finally, the proposed method was successfully used for the determination of BUs in real water and tea beverage samples.

In this study, the superparamagnetic attapulgite/Fe3O4/polyaniline (ATP/Fe3O4/PANI) nanocomposites were successfully synthesized by a one-pot method. Fe (III) was applied as both the oxidant for the oxidative polymerization of aniline and the single iron source of Fe3O4 formed by the redox reaction between aniline and Fe (III). The ATP/Fe3O4/PANI was used as sorbent for magnetic dispersive solid phase extraction (MDSPE) of benzoylurea insecticides (BUs) in environmental water samples. The as-prepared nanocomposite sorbents were characterized by Fourier transform infrared spectra (FT-IR), X Ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry. Various experimental parameters affecting the ATP/Fe3O4/PANI-based MDSPE procedure, including the composition of the nanocomposite sorbents, amount of ATP/Fe3O4/PANI nanocomposites, vortex time, pH, and desorption conditions were investigated. Under the optimal conditions, a good linearity was observed for all target analytes, with correlation coefficients (r(2)) ranging from 0.9985 to 0.9997; the limits of detection (LOD) were in the range of 0.02-0.43 μg L(-1), and the recoveries of analytes using the proposed method ranged between 77.37% and 103.69%. The sorbents exhibited an excellent reproducibility in the range of 1.52-5.27% in extracting the five target analytes. In addition, the intra-day and inter-day precision values were found to be in the range of 0.78-6.86% and 1.66-8.41%, respectively. Finally, the proposed ATP/Fe3O4/PANI-based MDSPE method was successfully applied to analyze river water samples by rapid preconcentration of BUs.

The neural crest is a multipotent population of migratory cells that arises in the central nervous system and subsequently migrates along defined stereotypic pathways. In the present work, we analyzed the role of a repulsive axon guidance protein, draxin, in the migration of neural crest cells. Draxin is expressed in the roof plate of the chick trunk spinal cord and around the early migration pathway of neural crest cells. Draxin modulates chick neural crest cell migration in vitro by reducing the polarization of these cells. When exposed to draxin, the velocity of migrating neural crest cells was reduced, and the cells changed direction so frequently that the net migration distance was also reduced. Overexpression of draxin also caused some early migrating neural crest cells to change direction to the dorsolateral pathway in the chick trunk region, presumably due to draxin's inhibitory activity. These results demonstrate that draxin, an axon guidance protein, can also affect trunk neural crest migration in the chick embryo.

The mesencephalic V neurons and tectobulbar axons in chick embryo project over long distances that appear during the early development of the chick optic tectum. The mesencephalic V neuron and tectobulbar axonal growth begin at Hamburger and Hamilton stage 14 and stage 18, respectively. Both fibers proceed downward from the dorsal to the ventral side of the lateral wall of the optic tectum and then turn caudally and join the medial longitudinal fasciculus. Their axons appear in the most superficial layer of the tectum at early stages and do not cross the dorsal midline of the tectum. Here, we report the role of draxin, a recently identified axon guidance protein, in the formation of the ventrally directed tectum axonal tracts in chicken embryo. draxin is expressed in a high dorsal to low ventral gradient in chick optic tectum. In vitro experiments show that draxin repels neurite outgrowth from dorsal tectum explants. In vivo overexpression resulted in inhibition or misrouting of axon growth in the tectum. Therefore, draxin may be an important member of the collection of repulsive guidance molecules that regulate the formation of the ventrally directed tectum axon tracts.

Axon guidance proteins are critical for the correct wiring of the nervous system during development. Several axon guidance cues and their family members have been well characterized. More unidentified axon guidance cues are assumed to participate in the formation of the extremely complex nervous system. We identified a secreted protein, draxin, that shares no homology with known guidance cues. Draxin inhibited or repelled neurite outgrowth from dorsal spinal cord and cortical explants in vitro. Ectopically expressed draxin inhibited growth or caused misrouting of chick spinal cord commissural axons in vivo. draxin knockout mice showed defasciculation of spinal cord commissural axons and absence of all forebrain commissures. Thus, draxin is a previously unknown chemorepulsive axon guidance molecule required for the development of spinal cord and forebrain commissures.

The influence of calcination temperature on the structure and catalytic behavior of Ni/TiO2-SiO2 catalyst, for CO2 reforming of methane to synthesis gas under atmospheric pressure, was investigated. The results showed that the Ni/TiO2-SiO2 catalyst calcined at 700° C had high and stable activity while the catalysts calcined at 550 and 850° C had low and unstable activity. Depending on the calcination temperature, one, two, or three of the following Ni-containing species, NiO, Ni2.44Ti0.72Si0.07O4, and NiTiO3 were identified by combining the temperature programmed reduction (TPR) and X-ray diffraction (XRD) results. Their reducibility decreased in the sequence: NiO > Ni2.44Ti0.72Si0.07O4 > NiTiO3. It suggests that high and stable activities observed over the Ni/TiO2-SiO2 catalyst calcined at 700°C were induced by the formation of Ni2.44Ti0.72Si0.07O4 and smaller NiO species crystallite size.

A 5 wt%Na2WO4–2 wt%Mn/SiC monolithic foam catalyst was applied in the oxidative coupling of methane. This catalyst showed the same high activity as the conventional 5 wt%Na2WO4–2 wt%Mn/SiO2 catalyst with no dilution gas and a temperature of 850 °C (>24% methane conversion, 51% C2 (ethylene and ethane) selectivity), but also an excellent heat transfer feature as the significant hot spots did not occur in the catalyst bed. The SiC- and SiO2-supported catalysts were characterized by BET, SEM, XRD and XPS, respectively.

Ni-nanoparticle-embedded mesoporous titania/silica catalyst was successfully synthesized in a one-pot process using homogeneous impregnation in sol–gel-derived titanium-silica gel, without any other organic additives and/or templating agents. The catalyst with NiO loading of 10 wt% and TiO2/SiO2 (wt) of 50:50 is highly catalytic active and stable for CO2 reforming of methane and its physicochemical properties were investigated by means of BET, H2-TPR, XRD, TEM and TG/DTA techniques, respectively. Under the condition of an atmospheric pressure at 850 °C and a gas hour space velocity (GHSV) of 1.8 × 10 4 ml h - 1 g cat - 1 , the conversion of CH4 and CO2 over 10 (wt%) NiO/TiO2–SiO2 (50:50) catalyst remained almost constant, at about 88% and 97%, for 30 h, respectively. The high activity and stability are attributed to the strong metal-support interactions, such as in Ni2.44Ti0.72Si0.07O4.

Carbon dioxide reforming of methane to synthesis gas has been investigated with Ni catalysts supported on SiC monolithic foam. The structure and properties of the catalysts were characterized by BET, SEM and XRD techniques. The novel catalysts exhibited not only the highest activity but also remarkable stability. Of which, 7 wt%Ni/SiC showed the highest activity at 750 °C, During the 100 h performance testing experiment on stream, the conversion of CH4 and CO2 remained almost constant, at about 94.0% and 95.0%, respectively.

Carbon dioxide reforming of methane to synthesis gas has been investigated with Ni catalysts supported on monolithic foam SiC, which were prepared by the initial wetness impregnation method. The catalyst of 7 wt%Ni/SiC was verified to be the best one in different Ni content catalysts. Compared with other catalysts such as 7 wt%Ni/SiO2 and 7 wt%Ni/Al2O3, the 7 wt%Ni/SiC catalyst exhibited not only the highest activity but also remarkable stability and excellent coke resistance during 100 h reaction. Furthermore, the conversion of CO2 and CH4 remained at about 96% and 94%, respectively in 100 h reaction time. The structure and properties of the catalysts were characterized by BET, XRD, H2-TPR, XPS and TEM techniques.

In this research, an effervescence-assisted β-cyclodextrin/attapulgite composite (β-CD/ATP) for the in-syringe dispersive solid-phase extraction (EAIS-DSPE) of pyrethroids in environmental samples was developed for the first time. A syringe was used to conduct the extraction procedure and a small amount of β-CD/ATP was dispersed into the solution with the release of carbon dioxide when the effervescent tablet components dissolved in water. Then, the sorbent was recovered using a filter membrane, and the analytes were directly eluted using acetonitrile. In the process, the β-CD/ATP sorbent resulted in an excellent extraction efficiency compared to commercially available sorbents such as C 18 and HLB. Moreover, in the extraction procedure, both the β-cyclodextrin inclusion interactions (especially the hydrophobic effects) and the special structure of the ATP contributed to the efficient enrichment of pyrethroids in aqueous media. The amount of β-CD/ATP sorbent, the volume of desorption, the ratio of NaH 2 PO 4 /Na 2 CO 3 , the volume of the sample, and the pH were screened using a Plackett–Burman design. All factors affecting the procedure were optimized by applying a central composite design. Under the optimized conditions, a good repeatability (RSDs) ranging from 1.7 to 2.3, linearity (2.5–500 μg L −1 ), limits of detection (LODs) (0.15–1.03 μg L −1 ), and an acceptable recoveries (76.8–86.5%) were achieved. Finally, the proposed method was successfully applied for the determination of pyrethroids in environmental samples including river water, reservoir water and lake water.

A simple, sensitive, and efficient method of using a pipette vial to perform dispersive liquid-liquid microextraction based on the solidification of floating organic droplets was coupled with high-performance liquid chromatography (HPLC) and a diode array detector for the preconcentration and analysis of four benzoylurea insecticides in fruit juice. In this method, 1-dodecanol was used as an extractant, and a snipped pipette was used as an experimental vial to simplify the procedure of collecting and separating solidified extractant. The experimental parameters were optimized using a Plackett-Burman design and one-factor-at-a-time method. Under the optimal conditions in the water model, the limits of detection for analytes varied from 0.03 to 0.28 μg/L, and the enrichment factors ranged from 147 to 206. Linearity was achieved for diflubenzuron and flufenoxuron in a range of 0.5-500 μg/L, for hexaflumuron in a range of 1-500 μg/L, and for triflumuron in a range of 5-500 μg/L. The correlation coefficients for the analytes ranged from 0.9986 to 0.9994 with recoveries of 91.4-110.9%. Finally, the developed technique was successfully applied to fruit juice samples with acceptable results. The relative standard deviations of the analytes at two spiking levels (50 and 200 μg/L) varied between 0.2 and 4.5%.

A green, simple, inexpensive dispersive solid-phase microextraction method coupled with high-performance liquid chromatography was developed for rapid screening and selective recognition of benzoylurea insecticides (BUs) in honey and tea beverages. A novel adsorbent, ionic liquid (IL)-modified β-cyclodextrin/attapulgite (β-CD/ATP), was prepared by immobilizing IL on the surface of β-CD/ATP. A series of demanding extraction conditions were investigated through the experimental design. Under optimum conditions, the limits of detection for the analytes varied from 0.12 to 0.21 μg L(-1). The enrichment factors ranged from 112 to 150 folds. Linearities in the range of 5-500 ng m L(-1) were achieved for four BUs, while the correlation coefficients ranged from 0.9997 to 1.0000 and the recoveries from 84.5% to 104.7%. The precision of this method for the four BUs corresponded to intra-day and inter-day RSDs% lower than 3.85%. Finally, the proposed technique was applied for the preconcentration of the BUs from real samples with satisfactory results.

A novel microextraction technique combining magnetic solid-phase microextraction (MSPME) with ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) to determine four fungicides is presented in this work for the first time. The main factors affecting the extraction efficiency were optimized by the one-factor-at-a-time approach and the impacts of these factors were studied by an orthogonal design. Without tedious clean-up procedure, analytes were extracted from the sample to the adsorbent and organic solvent and then desorbed in acetonitrile prior to chromatographic analysis. Under the optimum conditions, good linearity and high enrichment factors were obtained for all analytes, with correlation coefficients ranging from 0.9998 to 1.0000 and enrichment factors ranging 135 and 159 folds. The recoveries for proposed approach were between 98% and 115%, the limits of detection were between 0.02 and 0.04 μg L−1 and the RSDs changed from 2.96 to 4.16. The method was successfully applied in the analysis of four fungicides (azoxystrobin, chlorothalonil, cyprodinil and trifloxystrobin) in environmental water samples. The recoveries for the real water samples ranged between 81% and 109%. The procedure proved to be a time-saving, environmentally friendly, and efficient analytical technique.

A green, simple, and efficient method, ionic liquid-assisted liquid–liquid microextraction based on the solidification of floating organic droplets (ILSFOD-LLME) collected via a bell-shaped collection device (BSCD) coupled to high performance liquid chromatography with a variable-wavelength detector, was developed for the preconcentration and analysis of seven benzoylurea insecticides (BUs) in fruit juice. In the proposed method, the low-density solvent 1-dodecanol and the ionic liquid trihexyl(tetradecyl)phosphonium hexafluorophosphate ([P14, 6, 6, 6]PF6) were used as extractant. The extraction solvent droplet was easily collected and separated by the BSCD without centrifugation. The experimental parameters were optimized by the one-factor-at-a-time approach and were followed using an orthogonal array design. The results indicated the different effects of each parameter for extraction efficiency. Under the optimal conditions in the water model, the limits of detection for the analytes varied from 0.03 to 0.28 μg L−1. The enrichment factors ranged from 160 to 246. Linearities were achieved for hexaflumuron and flufenoxuron in the range of 0.5–500 μg L−1, for triflumuron, lufenuron and diafenthiuron in the range of 1–500 μg L−1, and for diflubenzuron and chlorfluazuron in the range of 5–500 μg L−1; the correlation coefficients for the BUs ranged from 0.9960 to 0.9990 with recoveries of 75.6–113.9%. Finally, the developed technique was successfully applied to real fruit juice with acceptable results. The relative standard deviations (RSDs) of the seven BUs at two spiked levels (50 and 200 μg L−1) varied between 0.1% and 7.3%.

A dispersive liquid-liquid microextraction method based on the solidification of floating organic droplets was developed as a simple and sensitive method for the simultaneous determination of the concentrations of multiple fungicides (triazolone, chlorothalonil, cyprodinil, and trifloxystrobin) in water by high-performance liquid chromatography with variable-wavelength detection. After an approach varying one factor at a time was used, an orthogonal array design [L25 (5(5))] was employed to optimize the method and to determine the interactions between the parameters. The significance of the effects of the different factors was determined using analysis of variance. The results indicated that the extraction solvent volume significantly affects the efficiency of the extraction. Under optimal conditions, the relative standard deviation (n = 5) varied from 2.3 to 5.5% at 0.1 μg/mL for each analyte. Low limits of detection were obtained and ranged from 0.02 to 0.2 ng/mL. In addition, the proposed method was applied to the analysis of fungicides in real water samples. The results show that the dispersive liquid-liquid microextraction based on the solidification of floating organic droplets is a potential method for detecting fungicides in environmental water samples, with recoveries of the target analytes ranging from 70.1 to 102.5%.

A novel, totally organic solvent-free emulsification microextraction (TEME) technique using ionic liquids (ILs) is proposed in this study. Seven bis(trifluoromethylsulfonyl)imide ionic liquids were synthesized. After comparing the physicochemical properties of the ionic liquids and their application to microextraction experiments, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6MIM][NTf2]), which has moderate surface tension and viscosity, was selected as the extraction solvent. The dispersion of ILs and mass transfer were accelerated by ultrasound irradiation and temperature control processes. Therefore, no dispersive organic solvent was needed. Several variables, such as ionic liquid volume, duration of the ultrasound extraction, dispersion temperature, ionic strength and centrifugation time were investigated and optimized. Under the optimum conditions, the calibration curve was linear in the range of 0.1-600 μg L(-1) for chlorfenapyr and fenpyroximate and 0.5-600 μg L(-1) for spirodiclofen, with correlation coefficients of 0.9994-0.9999. The enrichment factors were between 261 and 285. The limits of detection (LODs) were 0.02-0.06 μg L(-1). Real fruit juice samples (at fortified levels of 10 μg L(-1) and 30 μg L(-1)) were successfully analyzed using the proposed method. The relative recoveries and enrichment factors were in the range of 92-104%.

An in situ ionic liquid dispersive liquid-liquid microextraction (IL-DLLME) method was developed as a new approach for the detection of four pyrethroid pesticides in environmental water samples. The method is fast, simple, accurate and environmentally friendly. The hydrophobic ionic liquid, [C8MIM]-NTf2, formed by the water-soluble ionic liquid [C8MIM]Cl and the ion exchange reagent LiNTf2 was used as the extraction solvent. The experimental parameters affecting the extraction efficiency, including the amount of the IL, the extraction and the centrifugation times and the salt concentration were investigated and optimized using an orthogonal array design (OAD). A suitable molar ratio of LiNTf2 to [C8MIM]Cl on the recoveries of analytes was determined after OAD optimization. The method showed a good linear response in the range of 0.5 to 500 µg L-1 with correlation coefficients (R2) above 0.9998. The relative standard deviation (RSD) varied from 0.6 to 1.9%. The enrichment factor, the limit of detection and recovery ranged from 134 to 153, 0.02 to 0.18 µg L-1 and 89.7 to 95.6%, respectively. For water samples, the RSD ranged from 0.02 to 2.34% and the recovery ranges from 91.4 to 99.9%.

Generation of the appropriate types, numbers and distribution of neurons during the development of the nervous system requires the careful coordination of proliferation, differentiation, and patterning. In this work, we analyzed the roles of a repulsive axon guidance protein, draxin, on the development of chick spinal cord dI3 interneuron. draxin mRNA and/or protein were detected in the roof plate at first and then the boundary region between the ventricular and the mantle zones in chick spinal cord and dorsal basement membrane of the chick spinal cord. Overexpression of draxin caused the decreased and delayed migration of the dI3 interneuron, the reduction of progenitor cell proliferation, and abnormal localization of some ectopic progenitor-like cells in the mantle zone of the spinal cord. Our data reveal that draxin may be involved in the proper development of the dI3 interneuron in chick spinal cord. Developmental Dynamics 239:1654–1663, 2010. © 2010 Wiley-Liss, Inc.

The neural crest is a multipotent population of migratory cells that arises in the central nervous system and subsequently migrates along defined stereotypic pathways. In the present work, we analyzed the role of a repulsive axon guidance protein, draxin, in the migration of neural crest cells. Draxin is expressed in the roof plate of the chick trunk spinal cord and around the early migration pathway of neural crest cells. Draxin modulates chick neural crest cell migration in vitro by reducing the polarization of these cells. When exposed to draxin, the velocity of migrating neural crest cells was reduced, and the cells changed direction so frequently that the net migration distance was also reduced. Overexpression of draxin also caused some early migrating neural crest cells to change direction to the dorsolateral pathway in the chick trunk region, presumably due to draxin's inhibitory activity. These results demonstrate that draxin, an axon guidance protein, can also affect trunk neural crest migration in the chick embryo.

The hippocampus plays an essential role in learning and memory and is one of the major sites implicated in neural diseases. The proper organization of the hippocampus during development is important for its function. We found that draxin, a repulsive axon guidance cue, was widely expressed in the developing hippocampus and draxin deficient mice possessed a smaller hippocampus, particularly in the anterior part of the structure. Quantification of this reduction revealed that the volume of the dentate gyrus of the mutant was significantly smaller compared to the normal counterpart. This size reduction seemed to be dependent on apoptosis rather than due to a decrease in the rate of cell division.

Two ionic liquid-coated-Fe3O4 magnetic particles (IL-Fe3O4 MPs) were developed for use in two types of dispersive micro-solid phase extraction (D-μ-SPE) for the high-performance liquid chromatographic analysis of clofentezine and chlorfenapyr in environmental water samples. Self-assembling IL-Fe3O4 MPs were used in D-μ-SPE as adsorbents. Two D-μ-SPE extraction methods, namely, direct dispersive micro-solid phase extraction (d-D-μ-SPE) and in situ solvent formation-based dispersive micro-solid phase extraction (ISF-D-μ-SPE), were proposed, using [C8MIM][PF6] to extract analytes through two pathways. Lower IL doses were required in the extraction process compared with those in other IL-based methods. Fe3O4 MPs can also be recycled and reused after extraction and are thus environmentally friendly. These newly developed methods were demonstrated to be feasible for use in the quantitation of clofentezine and chlorfenapyr at trace levels, with lower limit of detection values ranging from 0.4 to 0.5 ng mL(-1) for d-D-μ-SPE and 0.4 ng mL(-1) for ISF-D-μ-SPE. Finally, relative standard deviations of less than 6.0% were obtained.

Draxin, a recently identified axon guidance protein, is essential for the formation of forebrain commissures, and can mediate repulsion of netrin-stimulated spinal commissural axons. Here, we report that draxin binds multiple netrin receptors: DCC (deleted in colorectal cancer), Neogenin, UNC5s (H1, H2, H3), and DSCAM (Down's syndrome cell adhesion molecule). SincedraxinandDccknockouts showed similar phenotype in forebrain commissures formation, we show here the functional importance of draxin/DCC interaction. Draxin interacts with subnanomolar affinity to the netrin receptor DCC, in a region of DCC distinct from its netrin-binding domain.In vitro, neurite outgrowth from cortical and olfactory bulb explants ofDccknock-out mice is significantly less inhibited by draxin, when compared with neurites from explants of wild-type mice. Furthermore, in comparison with wild-type mice, the growth cone collapse in response to draxin is largely abolished inDcc-deficient cortical neurons.In vivo, double heteros ofdraxin/Dccmice show markedly higher frequency of complete agenesis of corpus callosum than either of the single hetero. These results identify DCC as a convergent receptor for netrin and draxin in axon growth and guidance.

Draxin is a repulsive axon guidance protein that plays important roles in the formation of three commissures in the central nervous system and dorsal interneuron 3 (dI3) in the chick spinal cord. In the present study, we report the expression pattern of mouse draxin in the embryonic mouse trunk spinal cord. In the presence of draxin, the longest net migration length of a migrating mouse trunk neural crest cell was significantly reduced. In addition, the relative number of apolar neural crest cells increased as the draxin treatment time increased. Draxin caused actin cytoskeleton rearrangement in the migrating trunk neural crest cells. Our data suggest that draxin may regulate mouse trunk neural crest cell migration by the rearrangement of cell actin cytoskeleton and by reducing the polarization activity of these cells subsequently.