Composite carbon-fluoroplastic surface-layer sorbents for the rapid preconcentration of organic substances from aqueous solutions

The regularities of the dynamic solid-phase extraction of organic substances (exemplified by chloroform, butyl acetate, and diethyl ether) from aqueous solutions on composite surface-layer sorbents, in which a finely dispersed sorption-active carbon material (active carbon or nanocarbon) was supported onto the surface of porous polytetrafluoroethylene, were found. It was demonstrated that the efficiency of the sorbents developed was higher than that of traditional bulk porous sorbents used for the preconcentration of volatile organic substances from aqueous solutions.     

Formation and Physicochemical Features of Hybrid Threadlike Micelles in Aqueous Solution

We investigate the construction of long, stable hybrid threadlike micelles consisting of polyelectrolytes and oppositely charged surfactants in aqueous solution and examine the physicochemical features such as their structure and viscoelastic behavior in aqueous solution. The most important point for their construction is the careful control of interactions, especially electrostatic interactions, caused between the surfactants and polyelectrolytes. Incorporated polyelectrolytes are fully extended in these hybrid threadlike micelles irrespective of the molecular weight of the polymer. The viscoelastic behavior of the hybrid threadlike micellar solution is similar to that of ordinary threadlike micellar systems consisting of low‐molecular‐weight substances. However, the inclusion of polymers in the micelles causes differences in their mechanical properties.     

Development and use of extraction sample preparation in the chromatographic-mass spectrometric studies of cognac products

The distribution of ethanol and butanol between n-hexane and aqueous solutions of ammonium sulfate at 20 ± 1°C was studied over an ideal concentration region of the substances in the organic phase. The distribution constants of the substances and the increments of the methylene and hydroxyl groups of the alcohols in the logarithm of the distribution constant were calculated. It was found that an increase in the salt concentration in the aqueous phase resulted in a considerable increase in the increment of the methylene group and significantly improved the alcohol separation efficiency. The dependence of the distribution coefficients of ethanol and butanol on the concentration of ethanol in the aqueous phase was studied. A dramatic decrease in the increment of the methylene group was found as the ethanol concentration in the salt phase was increased above 4.5 vol %. A procedure was developed for extraction sample preparation for the subsequent determination of the characteristic components of cognac products and for the authentication of these products by gas chromatography. The essence of this procedure consists in the hexane extraction of butanol and other hydrophobic substances from cognac product samples prediluted with an aqueous solution of ammonium sulfate. In this case, the major portion of ethanol, as well as hydrophilic and thermally unstable impurities, which complicate analysis with direct sample injection, remained in the salt solution. The procedure was tested with 16 samples of cognac and cognac spirits from Georgia, including both authentic and adulterated products.     

应用分子印迹-固相萃取法提取中药活性成分非瑟酮

分别以中药黄栌的主要成分非瑟酮为印迹分子、 丙烯酰胺为功能单体及乙二醇二甲基丙烯酸酯为交联剂, 通过封管聚合法合成了分子印迹聚合物; 将其装于自制的固相萃取柱中, 研究了以不同体积比的乙醇-水溶液为溶剂时非瑟酮在柱上的保留行为; 通过优化清洗及洗脱条件, 使非瑟酮与它的结构相似物槲皮素在柱上得到了很好的分离.     

Extraction of cobalt from thiocyanate solutions with polyurethane foam

The extraction of cobalt (II) from aqueous thiocyanate solutions with polyurethane foam has been extensively investigated. The extraction is enhanced by high thiocyanate concentration, high ionic strength and low temperature. A pH of 1.0-9.0 can be used for efficient extraction. Cobalt can be extracted at low concentration and the distribution coefficient is independent of foam weight. Several foam types and foam pretreatments have been examined. The effect of various substances added to the cobalt thiocyanate solutions has been investigated. Some of these substances caused either enhanced or decreased extractions by interacting with the polyurethane foam or by changing the solution chemistry.     

衍生多孔碳材料在固相微萃取中的应用研究进展

固相微萃取是一种集采样、萃取、富集和进样于一体的样品前处理技术,其萃取效果与涂层材料密切相关。多孔碳材料具有比表面积大、多孔结构可控、活性位点多和化学稳定性好等优点,广泛应用于电池、超级电容器、催化、吸附和分离等领域,也是一种热门的用作固相微萃取探针的涂层材料。衍生多孔碳材料因种类丰富、可设计性强被广泛研究,研究主要集中在对衍生多孔碳材料的结构优化方面。但是衍生多孔碳材料在固相微萃取中的应用还存在如下问题:(1)共价有机框架衍生多孔碳材料的制备已取得较大进展,但将其应用于固相微萃取领域的研究仍较少;(2)有待进一步明确制备出的衍生多孔碳材料用作固相微萃取涂层表现出优异提取能力的机理;(3)有待进一步深入研究将衍生多孔碳材料用作固相微萃取涂层以实现对不同物理化学性质污染物的广谱高灵敏度分析。文章综述了近3年衍生多孔碳材料在固相微萃取中的应用研究,并展望了未来衍生多孔碳材料在固相微萃取中的研究前景。引用文献共56篇,主要来源于Elsevier。     

Focused microwave-assisted extraction combined with solid-phase microextraction and gas chromatography-mass spectrometry for the selective analysis of cocaine from coca leaves

An effective combination of focused microwave-assisted extraction (FMAE) with solid-phase microextraction (SPME) prior to gas chromatography (GC) is described for the selective extraction and quantitative analysis of cocaine from coca leaves (Erythroxylum coca). This approach required switching from an organic extraction solvent to an aqueous medium more compatible with SPME liquid sampling. SPME was performed in the direct immersion mode with a universal 100 microm polydimethylsiloxane (PDMS) coated fibre. Parameters influencing this extraction step, such as solution pH, sampling time and temperature are discussed. Furthermore, the overall extraction process takes into account the stability of cocaine in alkaline aqueous solutions at different temperatures. Cocaine degradation rate was determined by capillary electrophoresis using the short end injection procedure. In the selected extraction conditions, less than 5% of cocaine was degraded after 60 min. From a qualitative point of view, a significant gain in selectivity was obtained with the incorporation of SPME in the extraction procedure. As a consequence of SPME clean-up, shorter columns could be used and analysis time was reduced to 6 min compared to 35 min with conventional GC. Quantitative results led to a cocaine content of 0.70 +/- 0.04% in dry leaves (RSD <5%) which agreed with previous investigations.     

Application of molecular dynamics simulations in molecular property prediction II: diffusion coefficient

In this work, we have evaluated how well the general assisted model building with energy refinement (AMBER) force field performs in studying the dynamic properties of liquids. Diffusion coefficients (D) have been predicted for 17 solvents, five organic compounds in aqueous solutions, four proteins in aqueous solutions, and nine organic compounds in nonaqueous solutions. An efficient sampling strategy has been proposed and tested in the calculation of the diffusion coefficients of solutes in solutions. There are two major findings of this study. First of all, the diffusion coefficients of organic solutes in aqueous solution can be well predicted: the average unsigned errors and the root mean square errors are 0.137 and 0.171 × 10(-5) cm(-2) s(-1), respectively. Second, although the absolute values of D cannot be predicted, good correlations have been achieved for eight organic solvents with experimental data (R(2) = 0.784), four proteins in aqueous solutions (R(2) = 0.996), and nine organic compounds in nonaqueous solutions (R(2) = 0.834). The temperature dependent behaviors of three solvents, namely, TIP3P water, dimethyl sulfoxide, and cyclohexane have been studied. The major molecular dynamics (MD) settings, such as the sizes of simulation boxes and with/without wrapping the coordinates of MD snapshots into the primary simulation boxes have been explored. We have concluded that our sampling strategy that averaging the mean square displacement collected in multiple short-MD simulations is efficient in predicting diffusion coefficients of solutes at infinite dilution.     

Solid-phase microextraction from small volumes of sample in a glass capillary

A new sampling method is proposed for solid-phase microextraction (SPME), in which the extraction is carried out in a glass capillary containing a few microliters of sample. When an adsorption-type fiber is used for SPME, the equilibrium between aqueous sample and coating can be described by a Langmuir isotherm. Since the total amount of analytes and coexisting substances stays at a low level in a small volume of sample, the linear concentration range of analytes will be extended for SPME to be applied in quantification and the interference caused by sample matrix will be reduced. In addition, sampling in a capillary has a short diffusion distance and extraction equilibrium is established in 5-10 min. It is important in clinical analysis and therapeutic drug monitoring to be able to analyse sample volumes of samples. The feasibility of the new sampling method is demonstrated by the extractions of p-hydroxybenzaldehyde and a synthetic solution containing 1-naphthol, paeonol and 1-naphthylamine.     

Extracting hydrocarbons from water using a centrifuge

An original method for the solid-phase microextraction of hydrocarbons from water using a centrifuge is proposed. Comparative results from the chromatographic elution of substances after liquid-phase and solid-phase microextraction are presented. The percentage of the extraction of substances from aqueous solutions and the minimum detection limit for aromatic and aliphatic compounds are calculated.     

Determination of chlorophenols in soil samples by microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

Microwave-assisted extraction coupled to headspace solid-phase microextraction was studied and applied for one-step in-situ sample preparation prior to analysis of chlorophenols (CPs) in soil samples. The CPs in soil sample were extracted into the aqueous solution and then directly onto the solid-phase microextraction (SPME) fiber in headspace under the aid of microwave irradiation. After being desorbed from SPME fiber in the GC injection port, CPs were analyzed with a GC-electron-capture detection system. Parameters affecting the extraction efficiency such as the extraction solutions, the pH in the slurry, the humic acid content in the soil, the power and the irradiation time of microwave as well as the desorption parameters were investigated. Experimental results indicated that the extraction of a 1.0 g soil sample with a 6-ml aqueous solution (pH 2) and a polyacrylate fiber under the medium-power irradiation (132 W) for 9 min achieved the best extraction efficiency of about 90% recovery and less than 10% RSD. Desorption was optimal at 300 degrees C for 3 min. Detection limits were obtained at around 0.1-2.0 microg/kg levels. The proposed method provided a simple, fast, and organic solvent-free procedure to analyze CPs from soil sample matrix.     

Membrane-based solvent extraction for selective removal and recovery of metals

A membrane-based solvent extraction process was developed for selective removal and recovery of metals from aqueous solutions. The process utilizes microporous membranes as an interface between an aqueous solution and organic solvents containing liquid ion exchangers. Metal ions are transported from the aqueous solution to the organic phase at the interface created in the pores of membrane. The organic solvent, which is loaded with metal ions in the extraction module, is regenerated in contact with the stripping solution in the stripping module. One important feature of this process is the stability of the membrane system, which results from using an aqueous—organic separator to remove aqueous solution from the organic circulating line. This process was evaluated for enrichment of copper using solvents containing LIX 64N. The process is applicable to selective recovery of metals from ore leachates or metal-containing wastewater.     

The Study on Pervaporation Behaviors of Dilute Organic Solution Through PDMS/PTFE Composite Membrane

As an energy-efficient alternative to distillation, pervaporation has been widely combined with fermentation to remove organic compounds from their dilute solutions in a fermentation broth. In this work, the organic permselective composite membrane is prepared by coating polydimethylsiloxane (PDMS) cross-linked with n-heptane on the substrate of polytetrafluoroethylene(PTFE) membrane. The separation behavior is studied in different dilute organic solutions, which include acetone dilute solution, butanone dilute solution, cyclohexanone dilute solution, ethanol dilute solution, isopropanol dilute solution, n-butyl alcohol dilute solution, acetic acid dilute solution, and ethyl acetate dilute solution. Most of these solutions are main reaction products or by-products from fermentation process. The effects of solubility of organics in the membrane, molecular weight, and polarity of the organics on the pervaporation performance are investigated. The effects of operating temperature and organic concentration in the feed solutions on the performance of composite membrane are studied as well. The experimental results show that molecular volume has less influence than solubility and molecular polarity for these organic solvent. The selectivity of PDMS membrane to ethyl acetate is relative high due to good solubility and diffusion of ethyl acetate molecules in polymer.     

Strategies for the microextraction of polar organic contaminants in water samples

In this paper the most recent developments in the microextraction of polar analytes from aqueous environmental samples are critically reviewed. The particularities of different microextraction approaches, mainly solid-phase microextraction (SPME), stir-bar-sorptive extraction (SBSE), and liquid-phase microextraction (LPME), and their suitability for use in combination with chromatographic or electrically driven separation techniques for determination of polar species are discussed. The compatibility of microextraction techniques, especially SPME, with different derivatisation strategies enabling GC determination of polar analytes and improving their extractability is revised. In addition to the use of derivatisation reactions, the possibility of enhancing the yield of solid-phase microextraction methods for polar analytes by using new coatings and/or larger amounts of sorbent is also considered. Finally, attention is also focussed on describing the versatility of LPME in its different possible formats and its ability to improve selectivity in the extraction of polar analytes with acid-base properties by using separation membranes and buffer solutions, instead of organic solvents, as the acceptor solution.     

Solid-phase microextraction for the evaluation of partition coefficients of a chlorinated dioxin and hexachlorobenzene into humic substances.

We developed a method for the evaluation of the partition coefficients (K(oc)) of hexachlorobenzene (HCB) and 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) into humic substances (HSs) by using solid-phase microextraction (SPME). In the aqueous solution containing HCB or HpCDD and HS, the unbound species of HCB or HpCDD were accumulated on the SPME fiber. Subsequently, HCB or HpCDD on the SPME fiber was directly analyzed by GC-ECD. When the concentration of organic carbon in HS ([OC]) was plotted against the ratio of [HCB] or [HpCDD] in the absence of HS to that in the presence of HS, linear relationships were observed. The slope of the line corresponded to the K(oc) value. The log K(oc) values for HCB and HpCDD evaluated were in the ranges of 3.9 - 4.9 and 5.9 - 7.2, respectively. These values were the same order as those in the literature, which were evaluated by other methods (e.g., solubility enhancement, solid-phase extraction and dialysis). The relative standard deviations of the log K(oc) values evaluated in this study were within 5%.     

Chemically modified resins for solid-phase extraction

The packings most widely used for solid-phase extraction are hydrophobic and make poor surface contact with aqueous samples unless the resins are first treated with an activating organic solvent such as methanol. Insertion of an acetyl- or hydroxymethyl group into a porous polystyrene-divinylbenzene resin provides a more hydrophilic surface that is easily wetted by water alone. Small columns of the chemically modified resins were found to be very efficient for the solid-phase extraction of many types of organic solutes from aqueous samples. Comparative recovery studies showed that the modified resins are superior to both silica packings and unmodified organic resins for the solid-phase extraction of organic compounds, and especially for polar organics such as phenols.     

Selective sample treatment using molecularly imprinted polymers

The molecularly imprinted polymers (MIPs) are synthetic polymers possessing specific cavities designed for a target molecule. By a mechanism of molecular recognition, the MIPs are used as selective sorbents for the solid-phase extraction of target analytes from complex matrices. MIPs are often called synthetic antibodies in comparison with immuno-based sorbents; they offer some advantages including easy, cheap and rapid preparation and high thermal and chemical stability. This review describes the use of MIPs in solid-phase extraction with emphasis on their synthesis, the various parameters affecting the selectivity of the extraction, their potential to selectively extract analytes from complex aqueous samples or organic extracts, their on-line coupling with LC and their potential in miniaturized devices.     

Condensation and structure of silicic acid in tetrahydrofuran

Silicic acid (SA) was extracted with THF from aqueous sodium metasilicate (SMS) solutions neutralized with hydrochloric acid, followed by silylation to give silylated SA from which the condensation and structure of SA in tetrahydrofuran (THF) were investigated. The degree of extraction markedly depends on SA and HCl concentrations. The condensation of 0.86 and 3.5 mol/L SA-THF solutions was followed by measuring the viscosity of the solutions at 0 and 20°C. The silylated SA was isolated as a distillate (LS) and a residue (HS) with low and high M?_ns (ca. 1300 and 3800) by vacuum distillation. The ratio of LS against HS decreased as a SA concentration in THF increased. In an aqueous solution, SA exists as lower molecular weight SAs compared with those in THF. SAs such as monomer, dimer, cyclic tri- and tetramer were the main components in a 0.1 mol/L aqueous solution. On the extraction with THF from an aqueous solution, SA was found to undergo condensations to form more polymerized SAs. From the THF solutions of SA concentration above 0.5 mol/L, the HS was obtained as a main component (73%) which was expected to have ladder-like structures. © 1992 John Wiley & Sons, Inc.     

Use of solid-phase microextraction coupled with gas chromatography for the determination of residual solvents in pharmaceutical products

The aim of this work was to prove that solid-phase microextraction coupled with gas chromatography could be used for the determination and quantification of residual solvents in drugs. Four solvents were selected for the experiments: ethanol, cyclohexane, triethylamine and pyridine, together with a model powdered drug substance. Several kinds of fibers, together with the extraction mode, were evaluated to determine the most appropriate one for the simultaneous extraction of the four solvents. The most promising conditions were obtained with the Carboxen-polydimethylsiloxane fiber in the headspace of the aqueous solution that contained the dissolved powder. A concentrated phosphate buffer was added to the aqueous solution to set the pH at 9.6 in order to enable good extraction of triethylamine, and the optimum extraction time was experimentally determined. A multi-criteria optimization was also carried out by means of design of experiments to optimize remaining parameters: the extraction temperature was set at 40 degrees C, the ionic strength at 1.77 mol (l-1) and the volume of the aqueous solution at 7.2 ml. The method of standard additions was used for quantitative analysis. Its performance was evaluated and validated: the pooled RSD was around 15%, the limits of detection were all of the ppb level and the method was both accurate and linear.     

The specificity of a chlorphenamine-imprinted polymer and its application

A chlorphenamine-imprinted polymer was prepared in this study. Chromatographic analysis showed that the retentivity and selectivity of the imprinted polymer were greatly strengthened through molecular imprinting. As a consequence, chlorphenamine could be easily separated from diphenhydramine. Ionic interaction was proved to be the main power for the imprinted polymer to bind chlorphenamine. The strong extraction ability of the imprinted polymer for chlorphenamine in aqueous solution was evaluated further. It was shown that chlorphenamine, as low as 0.02 mumol l(-1), could be concentrated by 50 times with a recovery of more than 90% at pH 5. This study gave the potential of using the imprinted polymer for solid-phase extraction of practical samples.