Solid‐phase extraction using bis(indolyl)methane‐modified silica reinforced with multiwalled carbon nanotubes for the simultaneous determination of flavonoids and aromatic organic acid preservatives

A novel bis(indolyl)methane‐modified silica reinforced with multiwalled carbon nanotubes sorbent for solid‐phase extraction was designed and synthesized by chemical immobilization of nitro‐substituted 3,3′‐bis(indolyl)methane on silica modified with multiwalled carbon nanotubes. Coupled with high‐performance liquid chromatography analysis, the extraction properties of the sorbent were evaluated for flavonoids and aromatic organic acid compounds. Under optimum conditions, the sorbent can simultaneously extract five flavonoids and two aromatic organic acid preservatives in aqueous solutions in a single‐step solid‐phase extraction procedure. Wide linear ranges were obtained with correlation coefficients (R²) ranging from 0.9843 to 0.9976, and the limits of detection were in the range of 0.5–5 μg/L for the compounds tested. Compared with the silica modified with multiwalled carbon nanotubes sorbent and the nitro‐substituted 3,3′‐bis(indolyl)methane‐modified silica sorbent, the developed sorbent exhibited higher extraction efficiency toward the selected analytes. The synergistic effect of nitro‐substituted 3,3′‐bis(indolyl)methane and multiwalled carbon nanotubes not only improved the surface‐to‐volume ratio but also enhanced multiple intermolecular interactions, such as hydrogen bonds, π–π, and hydrophobic interactions, between the new sorbent and the selected analytes. The as‐established solid‐phase extraction with high‐performance liquid chromatography and diode array detection method was successfully applied to the simultaneous determination of flavonoids and aromatic organic acid preservatives in grape juices with recoveries ranging from 83.9 to 112% for all the selected analytes.     

Dispersive derivatization liquid-liquid extraction of degradation products/precursors of mustards and V-agents from aqueous samples

A new derivatization and extraction technique termed as dispersive derivatization liquid-liquid extraction (DDLLE) speeds up the analysis process by removing the requirement for drying of the sample. The derivatization process takes place at the interface between the analyte containing aqueous phase and derivatization agent laden organic phase. The organic phase is highly dispersed using disperser solvent so that the total surface area is large. The derivatizing agent used is 1-(heptafluorobutyryl)imidazole and the resulting heptafluorobutyryl (HFB) derivatized analytes are partitioned into the organic phase. In addition to reduced sample preparation time, for some of the analytes, the HFB derivatives provide better spectral differentiation between isomers than conventional trimethylsilyl (TMS) derivatives. Method parameters for the DDLLE, such as extraction, and disperser solvent and their volume, type and amount of base, amount of heptafluorobutyrylimidazole and extraction time were optimized on diisopropylaminoethanol (DiPAE), ethyldiethanolamine (EDEA), triethanolamine (TEA) and thiodiglycol (TDG). The DDLLE was also used on various real world samples, which also includes few OPCW organized proficiency test and a spiked urine sample. The observed limit of detection (LOD) with 1mL of sample for DDLLE in full scan with AMDIS was 10ng/mL and with methane chemical ionization, multiple reaction monitoring (MRM) was 100pg/mL, i.e., 100fg on-column.     

Magnetic carbon nanotubes synthesis by Fenton's reagent method and their potential application for removal of azo dye from aqueous solution

We report a simple and easy method to fabricate magnetic carbon nanotubes (CNTs) by Fenton's reagent method without the addition of any cations. H(2)O(2) was added slowly into the FeSO(4) solution mixed with purified CNTs, and the resulting reactants were placed into a quartz tube to undergo heat treatment under a nitrogen/hydrogen flow. Iron oxide (Fe(2)O(3)) nanoparticles were uniformly dispersed on CNTs without any pretreatment such as strong acid or covalent functionalization processes. The as-produced magnetic CNTs were used as an adsorbent for removal of methyl orange (MO) dye from aqueous solutions. Adsorption experiments indicated that the magnetic CNTs have good adsorption capacity (q(e)) of MO (28 mg/g). The Freundlich isotherm model fitted the experiment data better than the Langmuir isotherm mode. The mean energy of adsorption was calculated as 3.72 kJ/mol based on the Dubinin-Radushkevich model, which suggests that the removal process was dominated by physical adsorption. Kinetic regression results showed that the adsorption kinetics was more accurately represented by a pseudo second-order model. Intra-particle diffusion was involved in the adsorption process, but it was not the only rate-controlling step. More importantly, a new photocatalytic regeneration technology can be enabled by the high nanoscale iron oxide loading (50%). The magnetic CNT adsorbents could be effectively and quickly separated by applying an external magnetic field and regenerated by UV photocatalysis. Therefore, CNTs/λ-Fe(2)O(3) hybrid is a promising magnetic nanomaterial for preconcentration and separation of organic pollutants for environmental remediation.     

Effect of ethanol in the organic phase on liquid-liquid extraction in monosegmented flow analysis. Determination of zinc in drugs

In liquid-liquid extraction performed by monosegmented flow analysis (MSFA), the aqueous sample is introduced between two air bubbles and flows, under restricted dispersion, through a glass extraction tube where the analyte is retained, usually at pH higher than 8. The retained analyte is removed to a small volume of an organic phase containing a ligand which is introduced after the second air bubble. In this work, the effect of the organic phase composition on the extraction of Cu(II), Zn(II) and Cd(II) in MSFA systems was investigated by changing the ethanol content (0.1-4% v/v) in toluene, chloroform and carbon tetrachloride. The extracting efficiency of the organic phases containing ethanol was evaluated by using dithizone (DT), 1-2-pyridylazo-2 naphthol (PAN) and sodium diethyldithiocarbamate (DDTC) as ligands for the metals. The MSFA extraction system was improved by introducing a new syringe-based device for organic phase delivery. The presence of ethanol in the organic phase shows a remarkable (up to ten times) effect on the extraction efficiency of the flow system when DT is employed. Its presence is mandatory if DDTC is used, as it accounts for ligand solubility in the organic phase. The extraction efficiency also increases with the pH of the aqueous phase as a consequence of higher ionisation of the glass silanols, where the analytes are adsorbed before extraction. The system has been evaluated for determination of Zn(II) in drugs showing a mean R.S.D. of 2.2% and mean relative accuracy of 4.4%, when compared with atomic absorption spectrometry results. Typical sample frequency, sample and organic phase consumption are 30 samples per hour, 200 and 100 mul, respectively.     

Determination of acidic drugs in biological and environmental matrices by membrane‐based dual emulsification liquid‐phase microextraction followed by high‐performance liquid chromatography

A simple method is introduced providing a highly clean microextraction for the determination of some anti‐inflammatory drugs as the model analytes in human urine and environmental matrices. This method is based upon the implementation of two consecutive emulsification liquid‐phase microextractions, which are separated by a syringe filtration step. In this method, the organic extraction solvent (dihexyl ether) is dispersed into the aqueous sample solution (20 mL), and the resulting cloudy mixture is passed through a hydrophilic polytetrafluoroethylene syringe filter. By this action, the extraction phase containing the analytes and many interfering species that could be transferred into the organic phase is retained behind the hydrophilic membrane. The filter is then detached from the syringe and attached to another syringe containing an aqueous solution (pH 12.0, 150 μL), and by the in‐syringe dispersion of the organic phase into the aqueous phase, the analytes are selectively back‐extracted into the aqueous phase. The developed method is centrifuge‐free and very simple, and provides a high sample clean‐up in a few minutes. Under the optimized experimental conditions, the developed method provided a linearity in the range of 2.0–2000 ng/mL, a low limit of detection (0.5 ng/mL), and enrichment factors of 47–53.     

Comparative Study for the Removal of Oxadiazon from Aqueous Solutions by Adsorption on Chitosan and Activated Carbon

Abstract

In the present investigation, chitosan and activated carbon are used as adsorbents for the removal of oxadiazon from aqueous solutions. The analyzing system was a gas chromatograph equipped with mass selective detector. The equilibrium studies are systematically carried out in a batch process, covering various process parameters that include agitation time, adsorbent dosage, and pH of the aqueous solution. Also, the relationship between extraction of oxadiazon and volume of aqueous/organic phase as well as the effect of inorganic salt were investigated. Adsorption behavior was found to follow Freundlich and Langmuir isotherms. The adsorption mechanism is described by a pseudo-second-order kinetics.     

Carbon nanotubes as affinity probes for peptides and proteins in MALDI MS analysis

Recently, carbon nanotubes (CNTs) have been reported to be an effective MALDI matrix for small molecules (Anal. Chem.2003, 75, 6191). In a somewhat related study, we have employed CNTs produced by using NaH-treated anodic aluminum oxide (Na@AAO) as a reactive template as the assisting matrix for MALDI analysis upon the addition of high concentrations of citrate buffer. Our results indicate that the mass range can be extended to ca. 12,000 Da and that alkali metal adducts of analytes are effectively reduced. Furthermore, we have employed citric acid-treated CNTs as affinity probes to selectively concentrate traces of analytes from aqueous solutions. High concentrations of salts and surfactants in the sample solutions are also tolerated. This approach is very suitable for the MALDI analysis of small proteins, peptides, and protein enzymatic digest products.     

Salting out in organic solvents: a new route to carbon nanotube bundle engineering

In this study we investigate salt effects on bundle formation of carbon nanotubes (CNTs) dispersed in an organic solvent, N-methyl-2-pyrrolidone (NMP). Addition of NaI salt leads to self-assembly of CNTs into well-recognizable bundles. It is possible to control the size of the CNT bundles by varying the salt concentration.     

碳纳米管吸附水溶液中双酚A的热力学

以甲醇和去离子水组成的体系（体积比90∶10）为流动相,建立了以香烟过滤嘴作吸附剂,固相萃取（SPE）与高效液相色谱（HPLC）联用测定水中双酚A(Bisphenol A,BPA)的新方法。研究了水溶液中碳纳米管(CNTs)吸附双酚A的热力学特性,测定了不同温度下的吸附等温线,并探讨了其可能的吸附机理。结果表明,CNTs对BPA 的吸附主要以快速吸附为主,常温下,碳纳米管对于70 mg·L-1的双酚A水溶液的吸附量可达到 24.65 mg g-1,吸附量随初始浓度的增加而增加,随温度的降低而增大,采用Freundlich和Langmuir方程拟合,相关系数均大于0.99,热力学函数ΔG、ΔH及ΔS分别为-39.48 ~ -43.51 KJ·mol-1、-18.06 KJ·mol-1、71.73 J·mol-1·K-1,吸附为放热、熵增的自发过程,降低温度有利于吸附,并且具有物理吸附特征。     

Effects of solution chemistry on the adsorption of ibuprofen and triclosan onto carbon nanotubes

Single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and oxidized MWCNTs (O-MWCNTs) were studied for the adsorption of ibuprofen (IBU) and triclosan (TCS) as representative types of pharmaceutical and personal care products (PPCPs) under different chemical solution conditions. A good fitting of sorption isotherms was obtained using a Polanyi-Manes model (PMM). IBU and TCS sorption was stronger for SWCNTs than for MWCNTs due to higher specific surface area. The high oxygen content of O-MWCNT further depressed PPCP sorption. The sorption capacity of PPCPs was found to be pH-dependent, and more adsorption was observed at pHs below their pK(a) values. Ionic strength was also found to substantially affect TCS adsorption, with higher adsorption capacity observed for TCS at lower ionic strength. In the presence of a reference aquatic fulvic acid (FA), sorption of IBU and TCS was reduced due to the competitive sorption of FA on carbon nanotubes (CNTs). Sorption isotherm results with SWCNTs, MWCNTs and O-MWCNTs confirmed that the surface chemistry of CNTs, the chemical properties of PPCPs, and aqueous solution chemistry (pH, ionic strength, fulvic acid) all play an important role in PPCP adsorption onto CNTs.     

Adsorption and desorption of atrazine on carbon nanotubes

The potential impact of carbon nanotubes (CNTs) on human health and the environment is receiving more and more attention. The high surface area of CNTs tends to adsorb a large variety of toxic chemicals, which may enhance the toxicity of CNTs and/or toxic chemicals. In this study, adsorption and desorption of atrazine on carbon nanotubes from aqueous solution were studied through batch reactors. The adsorption equilibrium isotherms were nonlinear and were fitted by Freundlich, Langmuir, and Polanyi-Manes models. It was found that the Polanyi-Manes model described the adsorption process better than other two isotherm models. Together with the "characteristic curve," the Polanyi adsorption potential theory is applicable to describe the adsorption process of atrazine on CNTs. Thermodynamic calculations indicated that the adsorption reaction of atrazine on CNTs is spontaneous and exothermic. The desorption data showed that no significant desorption hysteresis occurred. High adsorption capacity and adsorption reversibility of atrazine on CNTs suggest that CNTs have high health and environmental risks, whereas they have potential applications for atrazine removal from water.     

Non‐Covalent Functionalization of Carbon Nanotubes with Surfactants and Polymers

Carbon nanotubes (CNTs) possessing unique structure and properties are attractive building blocks for novel materials and devices of important practical interest. However, the insolubility or poor dispersibility of pristine CNTs in common solvents poses a serious obstacle to their further development. To effectively utilize CNTs as building blocks for nanotechnology, CNTs have been covalently and noncovalently functionalized in a number of ways to render them soluble in aqueous or organic solutions. Here, we review recent progress and advances that have been made on dispersion of carbon nanotubes in aqueous and organic media by non‐covalent functionalization with surfactants and polymers.     

Solid phase microextraction assisted by droplets-based liquid-liquid microextraction for analysis of volatile aromatic hydrocarbons in water by gas chromatography

A new technique for the analysis of volatile aromatic hydrocarbons by combining liquid-liquid microextraction with solid phase microextraction has been developed. The analytes were extracted from aqueous samples by an immobilized polydimethylsiloxane fiber assisted by the droplets of an appropriate organic solvent. Benzene, toluene, ethylbenzene, and o-xylene were used as target analytes. The main factors potentially affecting the microextraction such as the nature and the volume of organic solvent, polydimethylsiloxane (PDMS) swelling, extraction time, agitation, temperature, and salts were optimized. The method requires a very low consumption of organic solvent. The relative enrichment factor is in the range of 7.1-32.4 for extraction in the presence of dichloromethane at an optimum volume of 18 μL mL(-1) of aqueous sample. This enhancement over regular polydimethylsiloxane fiber is primarily the result of the fiber swelling and of a stable thin layer of organic solvent attached to the surface of the PDMS fiber. The limit of detection ranges from 0.02 to 0.65 ng mL(-1) for the target compounds using a 7-μm bonded polydimethylsiloxane coating and a flame ionization detector. The validity of this method is demonstrated by the analysis of a real waste water sample.     

Oligoaniline assisted dispersion of carbon nanotubes in epoxy matrix for achieving the nanocomposites with enhanced mechanical,thermal and tribological properties

A critical challenge for initiating many applications of the carbon nanotubes (CNTs) is their dispersion in organic solvent or in polymer melt. In the present study, we described a novel strategy for fabricating carbon nanotubes (CNTs)-reinforced epoxy nanocomposite by utilizing aniline trimer (AT) as the noncovalent dispersant. Tensile testing showed that the tensile modulus of the CNTs-reinforced epoxy composites was considerably improved by adding a small amount of AT functionalized CNTs. Additionally, the as-prepared CNTs-epoxy nanocomposites exhibited superior tribological properties with much lower frictional coefficients and wear rates compared to those of neat epoxy resin. The well dispersed AT-functionalized CNTs in epoxy matrix played an important role in enhancing the mechanical properties, as well as acting as a solid lubricant for improving the tribological performance of epoxy/CNTs nanocomposite.     

A dispersive liquid-liquid microextraction using a switchable polarity dispersive solvent. Automated HPLC-FLD determination of ofloxacin in chicken meat

In this article, dispersive liquid-liquid microextraction (DLLME), based on the use of so-called switchable polarity dispersive solvent (SPDS) for microextraction, is presented for the first time. The new extraction technique makes use of a mixture of extraction solvent (dichloromethane) and the SPDS (acrylic acid). This mixture is injected into the aqueous sample solution, which was previously fortified with the alkaline agent (NaOH). The SPDS is dissolved in aqueous phase and a cloudy solution consisting of fine droplets of extraction solvent fully dispersed in the aqueous phase is observed. Simultaneously, as a consequence of the fast neutralization reaction, the SPDS investigated is converted into water-soluble salt and phase separation is achieved because the SPDS switches its polarity. Conversion of the SPDS excludes the negative influence of the conventional dispersive solvents used in DLLME on the solubility of target analytes in aqueous phase and, as a result, increases the DLLME efficiency.     

A Review on the Effects of Introducing CNTs in the Modification Process of Electrochemical Sensors

This review summarizes some developments in the fabrication of modified sensors and biosensors through the incorporating the carbon nanotubes (CNTs) in their modification ingredients. A large number of papers have paid attention towards the application of carbon nanotubes (CNTs) as electrode constituents and studied its electrochemical behavior. Here, we survey the achievements in the detection of various substances with high selectivity and sensitivity provided using CNTs based electrodes. Moreover, modified electrodes by CNTs have demonstrated the electrocatalytic features and higher sensitivity in detection of analytes. The improved characteristics arises from the large surface area and good conductivity of CNTs. However, it should be considered that the use of single walled carbon nanotubes (SWCNTs) or multi‐walled carbon nanotubes (MWCNTs), the presence of impurities, and the chemical procedures adopted are effective on the performance of the modified sensors.     

In-line phase separator for microfluidic solvent extraction of uranium

Experiments are carried out to study the separation of liquid-liquid dispersion generated at a microfluidic junction by using an in-line phase separator. The phase separator comprises a metallic mesh sandwiched between two flow channels. Dispersion generated at the microfluidic junction is fed to the upper flow channel of the in-line phase separator. Continuous phase permeates through the metallic mesh into the lower flow channel and gets separated from the dispersed phase. The effects of operating parameters (flow rates of the aqueous and organic phases), flow channel geometry and mesh properties (pore size and thickness) on phase separation are studied. After identification of operating window in which complete phase separation is achieved, mass transfer experiments are performed to demonstrate intensified uranium extraction using a micromixer and in-line phase separator.

     

Adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites

The adsorption of different alkanes (linear and cyclic), aromatics, and chlorohydrocarbons onto different nonmicroporous carbons--multiwalled carbon nanotubes (CNTs), carbon nanofibers (CNFs), and high-surface-area graphites (HSAGs)--is studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. HSAGs present the highest adsorption capacity, followed by CNTs and CNFs (although CNTs present an intermediate surface area between the two HSAG studied). Among the different adsorbates tested, benzene exhibits the highest adsorption capacity, and the same trend is observed in the enthalpy of adsorption. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene, and chloroform) with the surfaces are mainly dispersive over all the carbons tested, CNTs being the material with the highest dispersive contribution, as was deduced also from the entropy parameter. Adsorption parameters were correlated with morphological and chemical properties of the materials.     

微流控芯片停流液-液萃取技术的研究

基于微流控芯片的液-液萃取技术的研究是目前微流控芯片分析领域内的重要研究方向之一,与传统液-液萃取系统相比,萃取系统微型化所带来的优势表现为显著降低试样与试剂的消耗(仅为传统系统的万分之一)、分析速度快、易实现操作自动化和分析系统集成化。目前,在已报道的基于微流     

A microfluidic chip based sequential injection system with trapped droplet liquid-liquid extraction and chemiluminescence detection

A microfluidic chip-based sequential injection system with trapped droplet liquid-liquid extraction preconcentration and chemiluminescence detection was developed for achieving high sensitivity with low reagent and sample consumption. The microfabricated glass lab-chip had a 35 mm long extraction channel, with 134 shrunken opening rectangular recesses (L 100 microm x W 50 microm x D 25 microm) arrayed within a 1 mm length on both sides of the middle section of the channel. Ketonic peroxyoxalate ester solution was filled in the recesses forming organic droplets, and keeping the aqueous sample solution flowing continuously in the extraction channel; analytes were transferred from the aqueous phase into the droplets through molecular diffusion. After liquid-liquid extraction preconcentration, catalyst and hydrogen peroxide solutions were introduced into the channel, and mixed with analytes and peroxyoxalate ester to emit chemiluminescence light. The performance of the system was tested using butyl rhodamine B, yielding a precision of 4% RSD (n = 5) and a detection limit of 10(-9) M. Within a 17 min analytical cycle, the consumptions of sample and peroxyoxalate solutions were 2.7 microL and 160 nL, respectively.