Molecular dynamics simulation of pervaporation in zeolite membranes

The pervaporation separation of liquid mixtures of water/ethanol and water/methanol using three zeolite (Silicalite, NaA and Chabazite) membranes has been examined using the method of molecular dynamics. The main goal of this study was to identify intermolecular interactions between water, methanol, ethanol and the membrane surface that play a critical role in the separations. This would then allow better membranes to be designed more efficiently and systematically than the trial-and-error procedures often being used. Our simulations correctly exhibited all the qualitative experimental observations for these systems, including the hydrophobic or hydrophilic behaviour of zeolite membranes. The simulations showed that, for Silicalite zeolite, the separation is strongly influenced by the selective adsorption of ethanol. The separation factor, as a consequence, increases almost exponentially as the ethanol composition decreases. For ethanol dehydration in NaA and Chabazite, pore size was found to play a very important role in the separation; very high separation factors were therefore possible. Simulations were also used to investigate the effect of pore structure, feed compositions and operating conditions on the pervaporation efficiency. Finally, our simulations also demonstrated that molecular simulations could serve as a useful screening tool to determine the suitability of a membrane for potential pervaporation separation applications. Simulations can cost only a small fraction of an experiment, and can therefore be used to design experiments most likely to be successful.     

ToF-SIMS characterisation of diterpenoic acids after chromatographic separation

Microcolumn liquid chromatography (μHPLC) coupled on-line with time of flight secondary ion mass spectrometry (ToF-SIMS) was applied for mixture of diterpenoic acids (abietic, gibberellic and kaurenoic) analysis. Chromatographic effluent, with analytes separated, was carried out directly onto different, ToF-SIMS compatible surface substrates, for further ToF-SIMS analysis. Silica gel Si₆₀, aluminium backplate modified Si₆₀, monolithic silica gel and Raman spectroscopy chromatographic thin layers were used as the deposition substrates in this experiment. By ToF-SIMS surface imaging the deposition trace picture has been obtained. Effluent deposition surface area was scanned for diterpenoic acid fragment mass values based on mass spectrometric library. Measured ToF-SIMS dataset of fragment abundance and intensities were used for preliminary fragmentation schemes construction. The lowest substrate background activity has been established for monolithic silica gel thin layer and aluminium backplate modified Si₆₀ thin layer. In the case of Raman spectroscopy pre-treated thin layer or conventional chromatographic thin layer Si₆₀, the both, high background signal intensity and impossibility to construct negative ions surface image, were observed. Diterpenoic acids studied serve the similar mass spectrum but ToF-SIMS coupled with liquid chromatographic separation brings new impact to the positive identification of analytes studied.     

Sulphur dioxide plasma modification on poly(methyl methacrylate) for fluidic devices

We developed a sulphur dioxide plasma modification on a poly(methyl methacrylate) (PMMA) material for fluidic electrophoresis devices. The inner surface of the PMMA channel of a chip was modified by using sulphur dioxide plasma treatment. Contact angle measurements indicated that the buffer solutions were able to fill the capillary because of the hydrophilic property of the internal surface of the chip. XPS analysis indicated that the sulphur dioxide plasma treatment introduced a negative charge originating from the dissociation of the hydrogen atoms of sulphonic groups. Since this introduced a negative charge originating from strong acid sulphonic groups onto the surface of the channel, the electroosmotic flow (EOF) was observed to be large (∼7 × 10⁻⁴ m² V⁻¹ s⁻¹) and stable over a wide range of pH (4–10). The chip was fabricated by using plastic injection moulding methods for enabling the mass fabrication and disposable use of chips. The separation method is based on the net electric charge of the material, which enables the separation of identical samples on the basis of both isoelectric points and molecular weight. Two synthetic peptides with similar isoelectric points and molecular weights but different net charges were selected as model protein samples for the separation. The sample peptides were detected under fluorescence microscopy. The resulting electropherograms obtained by using the sulphur dioxide plasma-treated PMMA chip demonstrated that the two peptides were separated and that the migration time of the peptides was correlated with the net charge.     

Dynamics and applications of a microscale liquid surface interacting with an electric field

We analyze the dynamics of a microscale liquid surface interacting with a time-dependent electrostatic field. The analysis is based on Hamilton’s theory, which can deal with electrodynamics as well as mechanics. The analysis predicts that the mass of a liquid interacting with an electrostatic field is reduced as a result of its motion. The mass reduction occurs through the formation of a high-aspect liquid meniscus, which is eventually transformed to a molecular flow of the liquid. The high-aspect liquid meniscus is used to erect a CNT on the glass surface, and the molecular flow is used to initiate a plasma-induced reaction that produces a hydrogen-storing polymer.     

Multi‐commutated Flow‐through Multi‐optosensing: A Tool for Environmental Analysis

Abstract

Multi‐commutation, which refers to the use of solenoid valves to construct the flow network, has been widely used for providing automation in flow injection analysis. In this paper, the coupling of multi‐commutation and multi‐optosensing is developed for the analysis of two pesticides in environmental water samples, fuberidazole and o‐phenylphenol. In optosensing, the use of the solid support allows the discrimination between the analytes and other compounds that, if measuring in solution, would interfere in the analysis; in addition, the sensitivity needed when facing environmental samples is obtained. The two analytes are separated by using C₁₈ silica gel as solid support, taking into account their different kinetics of sorption/desorption when interacting with the solid support microbeads; the separation is performed in the same flow‐cell where the sensing detection is carried out (by using an additional amount of solid support in the cell itself above the irradiated microzone), so both separation and determination are integrated in the cell. The native fluorescence of fuberidazole and o‐phenylphenol was simultaneously measured at 314/356 and 250/345 nm, respectively. The detection limits obtained were 0.18 and 6.1 ng mL^?1 for fuberidazole and o‐phenylphenol respectively, with a sampling frequency of about 12 samples per hour. A recovery study was performed in waters obtained for wells and rivers, with satisfactory results.     

Marangoni flow and mass transfer of power-law non-Newtonian fluids over a disk with suction and injection

We scrutinize the approximate analytical solutions by the optimal homotopy analysis method (OHAM) for the flow and mass transfer within the Marangoni boundary layer of power-law fluids over a disk with suction and injection in the present paper. Concentration distribution on the surface of a disk varies in a power-law form. The non-Newtonian fluid flow is due to the surface concentration gradient without considering gravity and buoyancy. According to the conservation of mass, momentum and concentration, the governing partial differential equations are established, and the appropriate generalized Kármán transformation is found to reduce them to the nonlinear ordinary differential equations. OHAM is used to access the approximate analytical solution. The influences of Marangoni the number, suction/injection parameters and power-law exponent on the flow and mass transfer are examined.     

绕凸包主动流动控制的初步数值研究

基于程序可靠性校验,本文对绕凸包流动进行了数值研究,其中主要对不同吹／吸气速度影响进行了参数化研究,并根据结果对吹／吸气控制分离机理予以了解释,表明:吹吸气对附面层的吹断／吸除作用以及其对主流的气动堵塞作用是正确分析其影响分离机理的关键。     

基于耦合微流控芯片的可逆式铵检测及其影响因素研究

铵（NH+₄）的光谱检测有着重要的意义,随着微流控领域的发展,以快速性、便携性以及多组分检测为目标的微流控光谱分析成效卓著。但是分析中存在的指示剂浪费问题一直没有得到解决。锌卟啉作为一种天然的自发光分子,能够实现NH+₄的可逆性检测,解决这一问题,但却存在选择性低的缺点。针对这些问题,实验设计了一种耦合微流控芯片,由反应芯片、气体扩散芯片和检测芯片组成。其中反应芯片用于将NH+₄转化为NH₃,由聚二甲基硅氧烷制成;气体扩散芯片使NH₃扩散进入待测溶液,由上下两片玻璃芯片及夹在中间的一层PDMS材质的气体透过膜制成;而检测芯片则通过多层结构将指示剂固定在其中。指示剂是通过将锌卟啉永久染色在离子交换树脂上制作而成的,在遇到NH₃分子时会产生由绿到紫的变化,而当周围变成纯水环境时,又能够实现从紫到绿的逆向变化。以此耦合芯片为分析平台,搭建了一套小型化的光谱检测系统,以便携式光谱仪为分析器件,通过测量450 nm处的透射光谱强度变化,实现了NH+₄的定量检测,同时研究了影响检测结果的三个参数：气体透过膜厚度,流速和指示剂用量。首先通过光谱强度随时间的变化,我们证明了指示过程的可逆性,因而解决了指示剂浪费的问题,时间响应也说明了指示过程的快速性;接着通过与对照实验的对比,说明检测过程具有很高的选择性,能够排除干扰物的影响,光谱变化仅仅是因为NH₃的存在;通过改变气体扩散芯片中气体透过膜的厚度,得到了膜厚和光谱强度变化之间的关系,膜的厚度增加使得检测效果变差,但当膜厚小于10 μm时效果基本不变,考虑到机械强度,选择了10 μm作为膜的最佳厚度;随即研究了耦合芯片中流速对于光谱强度变化的影响,发现流速的增加会使得光谱强度变化减小,但流速小于5 μL·min-1时效果基本不变;最后又研究了指示剂用量对于光谱强度变化的影响,证明指示剂过多和过少都会影响检测效果,以5 mg为最佳。这套以耦合芯片为平台的光谱分析系统具有体积小,经济性高,响应迅速的特点,能够实现NH+₄高选择性、可逆性的定量测量。     

薄层色谱与表面增强拉曼散射光谱联用技术的研究进展

表面增强拉曼光谱（SERS）作为一种快速、灵敏的分析技术,被广泛应用于分析化学、环境检测及食品安全等领域。在实际生活中的样品大多为混合物,直接使用SERS技术无法对复杂样品中的分析物进行准确测定。薄层色谱（TLC）分离技术具有操作简便,成本低廉及分离速度快等特点,TLC作为一种高通量的分离技术在合成化学、分析化学、药物化学及食品科学等研究领域得到了广泛的应用。TLC对待测物体系进行分离后,通过碘显色或荧光对分离的斑点进行可视化处理,再结合质谱,红外光谱、荧光光谱及SERS光谱等分析技术可以对分离物质进行定性及定量分析。TLC与SERS联用技术的出现,使得SERS光谱可以应用于混合物中分析物的有效测定。TLC-SERS技术同时具备良好的分离作用和灵敏的光谱检测性能,适用于对复杂样品进行分离检测。在TLC-SERS检测过程中,样品用量少且无需使用复杂的实验设备即可实现对混合物现场快速检测。介绍了SERS的增强机理以及活性基底的制备,对TLC-SERS技术在环境污染物检测、食品安全、中草药鉴定及生物医学等方面的应用做了概括性综述。给出了TLC-SERS技术在有害物快检领域的应用实例,为TLC-SERS技术未来用于食品安全、法医鉴定及环境治理中快速检测方法建立及仪器设备研发提供参考。     

Separation followed by direct SERS detection of explosives on a novel black silicon multifunctional nanostructured surface prepared in a microfluidic channel

The article describes the multifunctionality of a novel black silicon (BS) nanostructured surface covered with a thin layer of noble metal prepared in the a microfluidic channel. It is focused on the separation properties of the BS substrate with direct detection of the separated analytes utilizing surface enhanced Raman spectroscopy. The same BS substrate is providing the stationary phase and a surface enhancement of the Raman signal that has been measured previously to be around 10. As tested molecules, the common components of explosives 1,3 dinitrobenzene and 2,4 dinitrotoluene were used. The separation of selected molecules was achieved with the dried toluene as a mobile phase in a 25 micrometers deep, 5 mm wide, and 4 cm long microfluidic channel during the 2 min. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation of zeolite-incorporated PDMS membranes for pervaporation separation of isopropanol-water mixtures

ZSM-5 zeolite-incorporated poly(dimethyl siloxane) membranes were prepared and molecular dispersion of zeolite in the membrane matrix was confirmed by scanning electron microscopy. After studying the behavior of membrane swelling at 30°C, the membranes were subjected to pervaporation separation of isopropanol-water mixtures at 30, 40 and 50°C. The effects of zeolite loading and feed composition on the pervaporation performances of the membranes were analyzed. Both permeation flux and selectivity increased simultaneously with increasing zeolite content in the membrane matrix. This was discussed on the basis of the enhancement of hydrophobicity, selective adsorption, and the establishment of molecular sieving action. The membrane containing the highest zeolite loading (30 mass%) exhibits the highest separation selectivity of 80.84 and flux of 6.78 × 10^?2kg/m²h at 30°C for 5 mass% of isopropanol in the feed. From the temperature dependency of diffusion and permeation values, the Arrhenius activation parameters were estimated. A pure membrane (M) exhibits higher E_p and E_D values compared to zeolite-incorporated membranes, signifying that permeation and diffusion require more energy for transport through a pure membrane, owing to its dense nature. Obviously, zeolite-incorporated membranes require less energy due to their molecular sieving action attributed to the presence of straight and sinusoidal channels in the framework of zeolite. All the zeolite-incorporated membranes exhibit positive ΔH_s values, suggesting that the heat of sorption is dominated by the Henry's mode of sorption.     

Developing a sensor for the simultaneous determination of adrenaline,uric acid,and tryptophan

A chemically modified electrode is constructed based on a coumestan derivative and multiwall carbon nanotubes modified carbon paste electrode (CMWCNT-CPE). The surface charge transfer rate constant, k _s, and the charge transfer coefficient, α, for the electron transfer between coumestan and MWCNT-CPE were estimated. CMWCNT-CPE presents a highly catalytic activity for adrenaline (AD) electrooxidation. The results show that the peak potential of AD at the CMWCNT-CPE surface shifted by about 145 mV toward negative values compared with that at the MWCNT-CPE surface. Differential pulse voltammetry exhibited three linear ranges and a detection limit of 0.2 μM for AD. For a mixture containing AD, uric acid (UA), and tryptophan (Trp), three signals corresponding to the analytes could well separate them from each other. Moreover, CMWCNT-CPE was used to determine AD in an adrenaline injection solution and UA in a human urine sample with satisfactory results. To confirm the proposed method, the AD injection solution and the urine sample were spiked with different certain amounts of AD, UA, and Trp.     

聚焦微波浸取-C18反相色谱柱分离-流动注射-电感耦合等离子体质谱联用技术测定龙胆草浸取液中的金属离子及其结合态

采用聚焦微波样品处理系统对中草药龙胆草进行水浸取处理，通过C18反相色谱柱对浸取液进行分离，此后采用流动注射－ICP－MS对其中的9种元素的游离态及结合态进行了测定，并研究了浸取条件对浸出率的影响。利用正交设计对微波浸取的条件（时间、温度、料液比）进行了优化。     

基于转捩SST模型凸起圆柱绕流数值研究

为了研究局部凸起对边界层转捩的影响,采用转捩SST模型分别对亚临界、临界和超临界状态下带突起的圆柱绕流问题进行了数值模拟,分析了不同Reynolds数下带突起的圆柱绕流问题的近壁面流动特征以及表面时均压力与摩擦力系数的分布和凸起对圆柱表面流动分离以及转捩的影响,对比了有无凸起两侧圆柱表面时均压力、摩擦力系数的不同. 结果表明:当来流Reynolds数处于临界区时,气流在圆柱上表面凸起处形成了3个反向旋转的漩涡,之后随着θ的增大,发生了流动分离和流动转捩现象;对于不同Reynolds数下的来流,圆柱上表面的凸起可以使气流发生转捩的位置提前;圆柱上表面的凸起使流速增大、压强降低,从而导致圆柱产生升力,随着来流Reynolds数的增大,其升力逐渐变大.      

侧风条件下短舱流动分离等离子体流动控制研究

利用数值仿真开展了侧风条件下短舱流动分离等离子体流动控制研究,首先研究了不同侧风条件下短舱流动分离特性,揭示了侧风角度以及速度大小对流动分离的影响规律.随着侧风角度的增加,进气唇口处分离区域不断扩大且进气截面的总压损失更加严重;随着侧风速度的变大,分离区域变化并不明显,进气截面总压损失系数降低.进一步将等离子体激励布置...     

壁面吸气抑制分离减少流动损失的研究

研究了斜流压气机具有大尺度分离的导向叶栅内的流场结构;通过对壁面不同吸气位置与吸气量对流场结构及损失的影响分析,并借助于拓扑分析的手段,探讨了针对于大尺度分离结构条件下吸气点位置的选择原则,总结出了端壁与吸力面吸气位置与分离结构之间的对应关系。     

离心叶轮内三维分离流态的拓扑分析

本文主要是用拓扑分析的方法,根据实验给出的流场信息,来确定流场结构的性质和研究这些性质随流动参数变化的规律,从而得到对流场特性的定性认识。这里着重讨论了离心叶轮内表面分离流态,指出叶片吸力面和压力面不同的分离形式,分析了叶片表面奇点分布规律,建立了叶道内三维流动分离模型。     

Validated LC-MS/MS method for quantification of agomelatine in human plasma and its application in a pharmacokinetic study

An analytical method based on liquid-liquid extraction has been developed and validated for analysis of agomelatine in human plasma. Fluoxetine was used as an internal standard for agomelatine. A Betasil C18 (4.0?×?100?mm, 5?μm) column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves simple isocratic chromatographic conditions and mass spectrometric detection in the positive ionization mode using an API-4000 system. The proposed method has been validated with linear range of 0.050-8.000?ng/ml for agomelatine. The intra-run and inter-run precision values are within 12.12% and 9.01%, respectively, for agomelatine at the lower limit of quantification level. The overall recovery for agomelatine and fluoxetine was 67.10% and 72.96%, respectively. This validated method was used successfully for analysis of plasma samples from a pharmacokinetic study.     

A non-equilibrium thermodynamic instability in shear-induced diffusion in polymer solutions

In the presence of shear flow, the constitutive equation for the diffusion flux in polymer solutions exhibits two kinds of coupling. One of these couplings comes from the viscous pressure contribution to the chemical potential, and the other one from the divergence of the viscous pressure tensor. The former contribution yields an effective diffusion coefficient depending on the viscous pressure, which may become negative in some circumstances. In such a case, an instability appears and the previously homogeneous system splits into two regions, with different solute concentrations – concentration banding. This separation depends on the polymer molecular mass and therefore it may provide a basis for the chromatographic separation of polymers of different molecular mass.     

利用质量流注入的流激孔腔噪声共振峰抑制

通过数值仿真揭示了开口前缘垂直注入质量流和前壁面平行注入质量流抑制流激孔腔噪声的机制,研究了多参数影响下脉动压力峰值降噪量和总降噪量随质量流注入速度的变化规律。开口前缘垂直注入质量流通过抬升剪切层,避免漩涡冲击开口后缘,抑制流激孔腔噪声脉动压力峰值;在一定范围内质量流注入速度越大,脉动压力峰值降噪量越大,但是低频部分引起的抬升也会越高,导致总降噪量先增大后减小;经优化后的峰值降噪量和总降噪量分别可以达到15dB和9.5dB。开口前壁面平行注入质量流则是通过加强开口处剪切层的稳定性,避免发生漩涡脱落,达到抑制流激孔腔噪声的目的;当质量流入口面积大于孔腔开口前壁面积2/3时,不仅可以显著降低流激孔腔噪声脉动压力的峰值,并且可以很好地抑制其它频段噪声的抬升;质量流注入速度为来流速度的0.5倍时,脉动压力峰值降噪量和总降噪量分别可以达到18dB和15.4dB。