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     

Enantioselective stopped-flow multidimensional gas chromatography. Determination of the inversion barrier of 1-chloro-2,2-dimethylaziridine

Enantioselective stopped-flow multidimensional gas chromatography (stopped-flow MDGC) is a fast and simple technique to determine enantiomerization (inversion) barriers in the gas phase in a range of delta G#gas(T)=70-200 kJ mol(-1). After complete gas-chromatographic separation of the enantiomers in the first column, gas phase enantiomerization of the heart-cut fraction of one single enantiomer is performed in the second (reactor) column at increased temperature and afterwards this fraction is separated into the enantiomers in the third column. From the observed de novo enantiomeric peak areas a(j), the enantiomerization time t and the enantiomerization temperature T, the enantiomerization (inversion) barrier delta G#gas(T) is determined and from temperature-dependent experiments, the activation enthalpy delta H#gas and the activation entropy delta S#gas are obtained. Enantiomerization studies on chiral 1-chloro-2,2-dimethylaziridine by stopped-flow MDGC yielded activation parameters of nitrogen inversion in the gas phase, i.e., delta G#gas(353 K)=110.5+/-0.5 kJ mol(-1), delta H#gas=71.0+/-3.8 kJ mol(-1) and delta S#gas=-109+/-11 J mol(-1) K(-1). By the complementary method of dynamic gas chromatography (GC), the apparent enantiomerization (inversion) barrier of 1-chloro-2,2-dimethylaziridine in the gas-liquid biphase system was found delta G#app(353 K)=108 kJ mol(-1). The values obtained by stopped-flow MDGC in the gas phase were used to calculate the activation parameters of nitrogen inversion of 1-chloro-2,2-dimethylaziridine in the liquid phase in the presence of the chiral selector Chirasil-nickel(II), i.e.. deltaG#liq(353 K)=106.0+/-0.4 kJ mol(-1), delta H#liq=68.3+/-1.4 kJ mol(-1) and deltaS#liq=-106+/-3.0 J mol(-1) K(-1).     

On-chip CO2 control for microfluidic cell culture

Carbon dioxide partial pressure (P(CO(2))) was controlled on-chip by flowing pre-equilibrated aqueous solutions through control channels across the device. Elevated P(CO(2)) (e.g. 0.05 atm) was modulated in neighboring stagnant channels via equilibration through the highly gas permeable substrate, poly(dimethylsiloxane) (PDMS). Stable gradients in P(CO(2)) were demonstrated with a pair of control lines in a source-sink configuration. P(CO(2)) equilibration was found to be sufficiently rapid (minutes) and stable (days) to enable long-term microfluidic culture of mammalian cells. The aqueous solutions flowing through the device also mitigated pervaporative losses at sustained elevated temperatures (e.g. 37 C), as compared to flowing humidified gas through the control lines to control P(CO(2)). Since pervaporation (and the associated increase in osmolality) was minimized, stopped-flow cell culture became possible, wherein cell secretions can accumulate within the confined environment of the microfluidic culture system. This strategy was utilized to demonstrate long-term (> 7 days) microfluidic culture of mouse fibroblasts under stopped-flow conditions without requiring the microfluidic system to be placed inside a cell culture incubator.     

Phase equilibrium calculations for unprocessed well streams containing hydrate inhibitors

It is shown that the phase distribution of methanol and water between a hydrocarbon gas phase, a hydrocarbon liquid phase and an aqueous phase can be represented using the Soave-Redlich-Kwong equation with a non-conventional mixing rule for the a-parameter suggested by Huron and Vidal. Model parameters are estimated from data for binaries of the type methanolhydrocarbon and waterhydrocarbon. New experimental data are presented for two reservoir fluids and for one model system. The paper further presents a phase equilibrium algorithm for calculating the phase boundaries and the equilibrium compositions at the phase boundary for a system consisting of a gas, a liquid and a mixed aqueous phase.     

Measurements of the desorption rate of sodium dodecyl sulfate from nylon particles by the stopped-flow method

The desorption kinetics of sodium dodecyl sulfate (SDS) from nylon particles was investigated by applying the stopped-flow technique. A stopped-flow spectrophotometer commercially available was modified in order to study the desorption kinetics of ionic surfactants from solid surfaces in aqueous solutions. The modification provided a mixing cell with platinum electrodes for electric conductivity detection. Nylon particle suspensions containing various concentrations of SDS were rapidly diluted with distilled water by using the modified mixing apparatus. The changes in specific electric conductivity with time were monitored by a memory-recorder system. It was found that the rate constant in the early stage of desorption could be accurately determined by the modified stopped-flow method.     

Determination of formaldehyde in frozen fish with formaldehyde dehydrogenase using a flow injection system with an incorporated gel-filtration chromatography column

A flow injection analysis (FIA) system for determination of formaldehyde in frozen fish products is described. The system provides a rapid and selective determination of formaldehyde in aqueous fish extracts by the combination of a deproteinization procedure and a stopped-flow enzymatic approach in a FIA system. The FIA system is furnished with a gel-filtration chromatography column for on-line removal of the proteins from the extract before the enzymatic analysis is performed. Compared with the standard methods for determination of formaldehyde in fish products the present method is much faster and less affected by interferences. The limit of detection for the proposed method is 2.5 mg/l of formaldehyde. The sampling frequency is about 10 determinations per hour.     

A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems

Vejrosta, J., Novák, J. and Jönsson, J.Å., 1982. A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems. Fluid Phase Equilibria, 8: 25–35.A method has been developed for measuring the partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems, based on the direct analysis of both phases. A gas mixture containing a known proportion of a volatile compound is drawn through the liquid (water) until equilibrium is established. A defined volume of the liquid phase is then withdrawn through a porous-polymer trap while maintaining the system at equilibrium. The residual water in the trap is then expelled by a stream of nitrogen gas, and the deposit remaining is thermally desorbed and analyzed by gas chromatography. This approach, together with an experimental technique for producing gas mixtures containing an accurately known concentration of hydrocarbon at low values, makes it possible to determine accurately the partition coefficients of low-solubility compounds, such as for hydrocarbons in aqueous systems, at very low solute concentrations in the system. The method has been verified by measuring the partition coefficient of hexane between the gas and liquid phases of an aqueous system at various concentrations and temperatures.     

Determination of pentachlorophenol by flow-injection analysis with spectrophotometric detection

Two FIA methods for the determination of pentachlorophenol, based on its oxidizing-condensation reaction with 4-aminoantipyrine in aqueous medium and spectrophotometric detection in the conventional and stopped-flow modes, are described. In both cases the calibration graphs are linear in the range from 1.0 to 60.0 mug/ml pentachlorophenol, with sampling rates of 48 and 28 samples/hr for triplicate analysis, respectively. Interferences from phenol and other chlorophenols have been evaluated. The stopped-flow method is particularly useful for determining pentachlorophenol in commercial formulations containing no more than 15% of other chlorophenols.     

Direct determination of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate by HPLC and GC methods

The high performance liquid chromatography and gas chromatography methods were investigated for their applicability in determining micro-level concentrations of tri-n-butyl phosphate (TBP). A high performance liquid chromatograph (HPLC) equipped with refractive index detector was used in determining TBP up to 2 ppm concentration level in the aqueous nitric acid solutions. The gas chromatography incorporated with Thermionic Detector (NPD) and Flame Photometric Detector (FPD) were examined for their potential in analyzing TBP in organic phase up to sub-ppm level. The results indicated that HPLC-RI technique is well suited for direct analysis of aqueous phase. For organic phase analysis, gas chromatographic methods with the TID and FPD were suitable but performance of detectors deteriorated often due to fouling.     

CO adsorption and oxidation at the catalyst-water interface: an investigation by attenuated total reflection infrared spectroscopy

Adsorption of carbon monoxide and oxidation of preadsorbed carbon monoxide from gas and aqueous phases were studied on a platinum catalyst deposited on a ZnSe internal reflection element (IRE) using attenuated total reflection infrared (ATR-IR) spectroscopy. The results of this study convincingly show that it is possible to prepare platinum metal layers strongly attached to an IRE, which are stable for over 3 days in aqueous-phase experiments. It is shown that ATR-IR spectroscopy is a suitable technique to study adsorption and catalytic reactions occurring at the interface of a solid catalyst in an aqueous reaction mixture, even with an extreme low-surface-area catalyst. Clearly, ATR-IR spectroscopy allows for a direct comparison of reactions on a catalytic surface in gas and liquid phases on the same sample. CO was found to adsorb both linearly and bridged on the platinum metal layer when adsorbed from the gas phase, but only linear CO was detected in aqueous solution, although with 5 times higher intensity. Oxidation of preadsorbed CO on platinum occurs in both gas phase, wetted gas, and aqueous media and was found to be 2 times faster in the aqueous phase compared to gas-phase oxidation because of a promoting effect of water. Moreover, during oxidation at room temperature, CO2 adsorbed on Pt/ZnSe was detected in both gas and aqueous phases.     

LYSIS OF EGG PHOSPHATIDYLCHOLINE LIPOSOMES BY SINGLET OXYGEN GENERATED IN THE GAS PHASE

Abstract Singlet molecular oxygen was generated in the gas phase by heterogeneous energy transfer from a film of dry Rose Bengal and bubbled into suspensions of egg phosphatidylcholine liposomes, leading to membrane lysis and lipid peroxidation. The analysis based on large target diffusion kinetics indicates that approximately 3000 interactions were required for lysis of 1.5 μm liposomes. This experimental method makes it possible to measure the reactivity of gas phase singlet oxygen with aqueous biological systems.     

A continuous two-phase reaction system coupled on-line with capillary chromatography for the determination of polar solutes in water

Gas chromatographic procedures are described for the determination of carboxylic acids and chlorinated anilines in water samples. Propionic acid and 2,6-difluorobenzoic acid in aqueous solution have been simultaneously alkylated and extracted by means of a continuous two-phase reaction system, and then quantitated by on-line coupled capillary gas chromatography; tetrahexyl-ammonium hydrogen sulfate was used as phase transfer catalyst and pentafluorobenzyl bromide as reagent. A factorial design approach was used to optimize on-line derivatization of aqueous propionic acid with regard to pH and concentration of phase transfer catalyst. Alkylation and extraction, under optimized conditions, followed by quantitation of the pentafluorobenzyl ester by flame ionization detection furnished a linear calibration for concentrations between 0.1 and 10 μg/ml. The relative standard deviation was 9–15 %. The continuous two-phase reaction system was also used to determine (chlorinated) anilines present in water at concentrations of 0.1–1 μg/ml; pentafluorobenzoyl chloride was used as reagent and analysis was performed by capillary gas chromatography with flame ionization or electron capture detection. The on-line acylation of p-chloroaniline was optimized with regard to pH, reagent concentration, and reaction time. The on-line reaction system worked satisfactorily for both applications, although excess reagent caused some problems with the chromatography.     

On the effect of low-energy electron induced DNA strand break in aqueous solution: a theoretical study indicating guanine as a weak link in DNA

In this theoretical study we have investigated the effect of low-energy electrons attached onto a 3'-guanine monophosphate, 3'-GMP, in the gas phase and in aqueous solution. DFT calculations with B3LYP/DZP++ were performed to study the C3'-O3' bond break of a 3'-GMP radical anion. Our results show that low-energy electrons, if attached to a 3'-GMP with a neutrally charged phosphate group, can easily induce a C3'-3' bond break in both the gas phase and aqueous solution. The activation energy was found here to be 10.3 kcal/mol in the gas phase and, even lower, 5.3 kcal/mol in aqueous solution. In comparison with calculated activation energies for other nucleotides the 3'-GMP has the lowest energy barrier in aqueous solution.     

Anion-Anion Complexes Established between Aspartate Dimers

Stable dimers aspartate-aspartate have been studied in aqueous and gas phase through theoretical simulations. The polarizable continuum model (PCM) has been applied to simulate the effect of the hydration on monomers and complexes. The quantum theory of atoms in molecules (QTAIM) and the interacting quantum atoms (IQA) scheme has been used to inquire into if, in the aqueous phase, individual hydrogen bonds have attractive electrostatic components. In all cases a spontaneous formation of the complexes in the aqueous phase are observed, while in the gas phase a considerable energy barrier must be overcome (between 100.8 to 263.2 kJ mol⁻¹). The intermolecular distance at which this barrier is indicates when the hydrogen-bond interactions begin to take importance between the dimers and the corresponding molecular recognition among them. The IQA analysis shows that in aqueous phase, the hydrogen bonds N−H⋅⋅⋅O are mainly electrostatic in nature with a certain covalent character which increases linearly with the decrease of internuclear distances H⋅⋅⋅O. The H⋅⋅⋅H interactions observed are stabilizing and they are mainly quantum in nature.     

Iron(II) complexes of 2,6-bis(5-alkyl-1,5-dimethyl-4,5-dihydro-1H-imidazol-4-on-2-yl)pyridine ligands. Synthesis, characterisation and solvolytic stability

New 2,6-bis(5-alkyl-1,5-dimethyl-4,5-dihydro-1H-imidazol-4-on-2-yl)pyridines have been prepared and characterized by ¹H-, ¹³C-NMR and elemental analysis. These ligands form complexes with FeCl₂, which were isolated and characterized by elemental analysis and MS. Both in the solid phase and in aqueous and methanolic solutions the complexes have two ligand molecules per one ferrous ion. By means of the kinetic stopped-flow method, the rate constants of acid catalyzed decomposition, which proceeds as a system of two consecutive reactions, were determined. It was found that increasing steric demands of 5-alkyl substituent in the 4,5-dihydro-1H-imidazol-4-one cycle significantly retards the acid catalyzed solvolysis. The methyl derivative is solvolyzed cca two orders faster than the corresponding t-Bu derivative.     

Measurement of absorption coefficients in vapour-phase infrared spectra by means of gas chromatographic-infrared systems

In addition to stopped-flow gas chromatographic-infrared (GC-IR) systems and static vapour cells, GC-IR systems without a stopped-flow facility can also be used to measure vapour-phase IR spectra of appropriate quality. An expression was derived for the determination of concentrations in this type of measurement, which can be used to determine integrated absorption coefficients of practical and theoretical importance.     

金属离子与腺嘌呤异构体复合物的稳定性

在B3LYP/6-311++G**//6-31+G*基组水平上结合PCM模型系统的优化了气相和液相环境中14种腺嘌呤异构体与四种金属离子(Na+,K+,Mg2+,Ca2+)形成的132个稳定复合物。通过能量对比,得到了所有复合物异构体在气液两相中的稳定性顺序及不同金属离子与同一异构体形成的复合物的能量排序,首次给出了液相中这些不同金属离子复合物的最稳定结构。结果发现溶剂效应导致了液相中的复合物稳定性顺序与气相中的相比发生了很大变化;同一异构体与不同金属离子形成的复合物其稳定性在排序中也变化很大。对于这些变化,本文分别从金属离子与腺嘌呤的复合物在气相中的结合能(EBE)及在液相中的溶质溶剂相互作用能(Epol)能等方面进行了系统的阐述     

Use of the three-phase model and headspace analysis for the facile determination of all partition/association constants for highly volatile solute–cyclodextrin–water systems

A versatile method for measuring the partition coefficients of volatile analytes with an aqueous pseudophase using headspace gas chromatography is reported. A “three-phase” model accounts for all equilibria present in the system, including the partitioning of the analyte in the gas and aqueous phases to the pseudophase. This method is applicable to a wide variety of volatile analytes and aqueous pseudophases, providing that sufficient pseudophase may be used to reduce the analyte partial pressure. Generally, the method offers good reproducibility and high sensitivity. The associations of five volatile analytes (hydrogen sulfide, methanethiol, dimethyl sulfide, dichloromethane, and ethyl ether) with various cyclodextrins were examined. All analytes were found to partition preferentially to the cyclodextrin pseudophase compared to the aqueous phase. In addition, several analyte–cyclodextrin combinations formed insoluble complexes in solution that enhanced the extraction of the analyte from the gas and aqueous phases. Derivatization of the cyclodextrins generally decreased the extent of analyte–cyclodextrin interaction.     

Direct determination of several elements in MIBK extract by high-power nitrogen-oxygen mixed gas microwave-induced plasma optical emission spectrometry

A nitrogen-oxygen mixed gas microwave-induced plasma with an Okamoto cavity was employed as an atomization and excitation source for emission spectrometric analysis of organic solvent samples. Nitrogen–oxygen mixed gas produces very a stable microwave-induced plasma that is highly robust to the loading of 4-methyl-2-pentanone (MIBK), possibly because the organic solvent is completely combusted in the oxygen-containing plasma. After extracting test solutions containing Al, Co, Cr(III), Cu, Fe(III), Mo(VI), Ni, Pb with MIBK, both the aqueous phase and the organic phase were aspirated into the microwave-induced plasma, yielding linear calibration curves for both the species in the aqueous phase (Al, Co, Cr, Ni, and Pb) and those in the organic phase (Fe and Mo). These results indicate that Fe and Mo can be extracted with MIBK, which is explained by the partition coefficients of these elements in MIBK.     

A computational study on the decomposition of formic acid catalyzed by (H2O)x, x = 0-3: comparison of the gas-phase and aqueous-phase results

The mechanisms for the water-catalyzed decomposition of formic acid in the gas phase and aqueous phase have been studied by the high-level G2M method. Water plays an important role in the reduction of activation energies on both dehydration and decarboxylation. It was found that the dehydration is the main channel in the gas phase without any water, while the decarboxylation becomes the dominant one with water catalyzed in the gas phase and aqueous phase. The kinetics has been studied by the microcanonical RRKM in the temperature range of 200-2000 K. The predicted rate constant for the (H 2O) 3-catalyzed decarboxylation in the aqueous phase is in good agreement with the experimental data. The calculated CO 2/CO ratio is 200-74 between 600-700 K and 178-303 atm, which is consistent with the average ratio of 121 measured experimentally by Yu and Savage (ref 3).