Continuous-flow extraction of colloidal components in aqueous samples

In this study we report the development and performance of a system for continuous-flow extraction of dissolved and colloidal analytes in an aqueous matrix. Initial studies, using a classical segmented-flow extraction procedure, showed poor extraction efficiency for the hydrophobic colloidally dispersed analytes. Insufficient contact between the extractant and the colloidal constituents seems to be the primary reason for poor extraction. Improved performance is obtained when mechanical energy is added to the system, to effect a forced contact between the sample and the solvent. This was accomplished by injecting the extractant, with a high velocity, into the continuous flow of analyte through a narrow-bore nozzle. In this way, the solvent stream is dispersed into fine droplets with high kinetic energies. A region of intense turbulence is created, which was studied by high-speed photography using pulsed laser fluorescence. Comparison with classical flow extraction, using a model sample of colloidal wood resin compounds in water, showed that the dissolved components extracted well with both systems, while an extraction enhancement of up to 9 times was experienced with colloidal triglycerides.     

Pressurized hot water extraction with on-line fluorescence monitoring: a comparison of the static,dynamic, and static-dynamic modes for the removal of polycyclic aromatic hydrocarbons from environmental solid samples

A comparison of the feasibility of the three operational modes of pressurized hot solvent extraction (PHSE) (namely, static, where a fixed extractant volume is used; dynamic, where the extractant continually flows through the sample; and static-dynamic mode, which consists of a combination of the two previous modes) for the extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental solid samples (such as soil, sediment, trout, and sardine) has been performed. In all cases, a sodium dodecyl sulfate (SDS) aqueous solution was used as leaching agent. The use of a flow injection manifold between the extractor and a molecular fluorescence detector allowed real-time on-line fluorescence monitoring of the PAHs extracted from the samples, thus working as a screening system and providing qualitative and semiquantitative information on the target analytes extracted from both natural and spiked samples. The on-line monitoring option allowed the extraction kinetics to be monitored and the end of the leaching step to be determined independently of the sample matrix, thereby reducing extraction times. Efficiencies close to 100% have been provided by the three modes, which differ in the extraction time required for total removal of the target compounds. The time needed for the dynamic mode was shorter than that for the static mode. However, the establishment of a static extraction step prior to dynamic extraction was the key to shorten the time required for complete extraction. The method has been applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation.     

纵向超声波辅助微注塑方法

微注塑过程中,聚合物熔体在微小腔体中流动时充模阻力比常规注塑大,这影响了熔体填充效果,同时热量损失的不均衡性和不确定性容易导致注塑精度不高．提出了纵向超声波辅助微注塑方法,并对超声波振动对聚合物熔体的作用机理进行了探讨,分析了超声换能器结构对应力、振幅和响应频率的影响．基于对微注塑过程的模拟结果,开发了纵向超声波辅助微注塑装置．通过在微注塑过程中纵向超声波对熔体的能量作用降低熔体黏度,改善了熔体流动和充填性能．为了验证超声波辅助微注塑的效果,进行了菲涅尔透镜实际注塑实验．实验结果表明,相同的注塑工艺条件下,超声辅助微注塑过程中聚合物熔体的充填性能提高了6．91％．     

Sampling and electrophoretic analysis of segmented flow streams using virtual walls in a microfluidic device

A method for sampling and electrophoretic analysis of aqueous plugs segmented in a stream of immiscible oil is described. In the method, an aqueous buffer and oil stream flow parallel to each other to form a stable virtual wall in a microfabricated K-shaped fluidic element. As aqueous sample plugs in the oil stream make contact with the virtual wall, coalescence occurs and sample is electrokinetically transferred to the aqueous stream. Using this virtual wall, two methods of injection for channel electrophoresis were developed. In the first, discrete sample zones flow past the inlet of an electrophoresis channel and a portion is injected by electroosmotic flow, termed the "discrete injector". With this approach at least 800 plugs could be injected without interruption from a continuous segmented stream with 5.1% RSD in peak area. This method generated up to 1,050 theoretical plates, although analysis of the injector suggested that improvements may be possible. In a second method, aqueous plugs are sampled in a way that allows them to form a continuous stream that is directed to a microfluidic cross-style injector, termed the "desegmenting injector". This method does not analyze each individual plug but instead allows periodic sampling of a high-frequency stream of plugs. Using this system at least 1000 injections could be performed sequentially with 5.8% RSD in peak area and 53,500 theoretical plates. This method was demonstrated to be useful for monitoring concentration changes from a sampling device with 10 s temporal resolution. Aqueous plugs in segmented flows have been applied to many different chemical manipulations including synthesis, assays, sampling processing and sampling. Nearly all such studies have used optical methods to analyze plug contents. This method offers a new way to analyze such samples and should enable new applications of segmented flow systems.     

Fluidic preconcentrator device for capillary electrophoresis of proteins

A new preconcentration device was developed for analysis of proteins by capillary electrophoresis (CE). The microfluidic device uses an electric field to capture proteins that pass through the system. The capture zone is maintained in the flow stream by the interaction between hydrodynamic and electrical forces. The device consists of a flow channel made of PEEK tubing with two electrical junctions, each of which is covered with a conductive membrane. A syringe pump provides the flow stream and also allows the injection of up to 13.5 microL of a dilute sample. The system can be easily connected to a CE device postcapture for off-line preconcentration of proteins. For the proteins used in this study, preconcentration factors up to 40-fold can be achieved. CE detection limits for bovine carbonic anhydrase, alpha-lactalbumin and beta-lactoglobulins A and B were in the nanomolar range using UV detection at 200 nm. Preconcentration is dependent on both time and initial protein concentration. We show the possibility of using an off-line fluidic preconcentrator device employing counterflow capillary electrophoresis with minimum sample manipulation, achieving detection limits similar to on-line approaches.     

A mathematical model for kinetic study of analyte permeation from both liquid and gas phases through hollow fiber membranes into vacuum

A mathematical model and a Matlab-5 computer code have been developed to study the dynamic response of the hollow fiber membrane probe. The depletion layer formation at the sample/membrane interface is taken into consideration by the mathematical model for the liquid mobile phase. The code produces concentration profiles within a sample feed stream and in the membrane. Flux values at the vacuum side of the membrane can also be calculated as a function of time. The method can be applied both for gas and liquid feed streams. Concentration profiles in a mobile phase and the flux of analytes through the hollow fiber membrane inlet have been studied with this simulation technique as a function of the liquid-phase flow rate. The influence of the formation of a layer of the analyte depletion during the dynamic response has been considered. The shape of the depleted layer and selectivity of permeation from a liquid mobile phase through the membrane into the vacuum are shown to be dependent on the mobile-phase flow rate. In addition, for studied conditions, formation of a depletion layer is demonstrated to be fast compared with membrane diffusion. Thus, if a homogeneous aqueous sample is coming through the inlet cross-section of a hollow fiber membrane containing pure water, the response time mostly depends on analyte diffusivity in the membrane. However, if the aqueous sample is coming through the inlet cross-section of a hollow fiber membrane containing clean air, response time also depends on equilibrium analyte concentration in the depletion layer.     

Continuous determination of high-vapor-phase concentrations of tetrachloroethylene using on-line mass spectrometry

A method was developed to determine the vapor concentration of tetrachloroethylene (PCE) at and below its equilibrium vapor-phase concentration, 168 000 microg/L (25 degrees C). Vapor samples were drawn by vacuum into a six-port sampling valve and injected through a jet separator into an ion trap mass spectrometer (MS). This on-line MS can continuously sample a vapor stream and provide vapor concentrations every 30 s. Calibration of the instrument was done by creating a saturated stream of PCE vapor, sampling the vapor with the on-line MS and with thermal desorption tubes, and correlating the peak area response from the MS with the vapor concentration determined by automated thermal desorption gas chromatography mass spectrometry. Dilution of the saturated stream provided lower concentrations of PCE vapor. The method was developed to monitor the vapor concentration of PCE that was sparged from a two-dimensional flow chamber and for determination of the total PCE mass removed during each sparge event. The method has potential application for analysis of gas-phase tracers.     

Boron removal by membrane contactors: the water that purifies water

The potential of membrane contactors for treating boron containing waters were investigated. In particular, experimental tests at lab scale on flat membrane modules with 40 cm² of membrane area were carried out, to identify the effect of different parameters, such as temperature, flow rate, boron concentration, etc. on the efficiency of the process. Water was chosen as the extractant in order to avoid the pollution of the feed stream and two symmetric microporous hydrophilic flat membranes with different pore size and porosity were used. From these tests, it results that the boron removal increases with the extractant temperature and with the operating flow rates. However, it is independent on the initial boron concentration in the feed water. Moreover, higher removals are obtained with the membrane with larger pore size and higher porosity. Based on the experimental results, an integrated reverse osmosis-membrane contactor system, where the membrane contactor works on the reverse osmosis permeate, was proposed and designed for a 100 m³/h fresh water production (with a boron content ≤0.4 ppm). In particular, membranes with higher porosity and lower thickness than those used in the experimental tests were considered for the calculations, in order to work at 25°C (so, there is no need of heating the extractant stream) with reasonable membrane areas. The comparison of the proposed plant to that actually used, has shown that the proposed one appears to be more effective in terms of size, energy and chemical consumption, flexibility and modularity.     

四通道中空纤维NaA分子筛内膜的制备与表征

采用错流真空抽吸涂晶与动态水热合成的方法在四通道陶瓷中空纤维载体的内表面制备出高性能的NaA分子筛膜, 并用于75℃下90wt%乙醇/水混合物渗透汽化脱水分离, 系统考察了晶种液流速、涂晶时间与合成温度对NaA分子筛膜形貌与分离性能的影响。结果表明, 当晶种液流速为100 mL/h、涂晶时间为5 s时制备的NaA分子筛膜致密均匀; 晶种液流速过慢或者涂晶时间过长会导致膜厚增加同时也会在膜表面产生缺陷。当膜在100℃下水热合成两次, 制备的NaA分子筛膜分离性能最佳, 此时膜的分离因子为1585, 通量高达8.8 kg/(m²•h)。当合成温度过低时, 膜的晶化程度较低, 膜表面出现缺陷; 当合成温度过高时, 膜晶体生长速率过快, 交互生长程度较差, 膜的断面产生缺陷, 导致膜分离性能较低。     

Improved temporal resolution for in vivo microdialysis by using segmented flow

Microdialysis sampling probes were interfaced to a segmented flow system to improve temporal resolution for monitoring concentration dynamics. Aqueous dialysate was segmented into nanoliter plugs by pumping sample stream into the base of a tee channel structure microfabricated on a PDMS chip that had an immiscible carrier phase (perfluorodecalin) pumped into the cross arm of the tee. Varying the oil flow rate from 0.22 to 6.3 microL/min and sample flow rate from 42 to 328 nL/min allowed control of plug volume, interval between plugs, and frequency of plug generation between 6 and 28 nL, 0.6 and 10 s, and 0.1 and 1.7 Hz, respectively. Temporal resolution of the system, determined by measuring fluorescence in individual sample plugs following step changes of fluorescein concentration at the sampling probe surface, was as good as 15 s. Temporal resolution was independent of both sampling flow rate and distance that samples were pumped from the sampling probe. This effect is due to the prevention of Taylor dispersion of the sample as it was transported by segmented flow. In contrast, without flow segmentation, temporal resolution was worsened from 25 to 160 s as the detection point was moved from the sampling probe to 40 cm downstream. Glucose was detected by modifying the chip to allow enzyme assay reagents to be mixed with dialysate as sample plugs formed. The resulting assay had a detection limit of 50 microM and a linear range of 0.2-2 mM. This system was used to measure glucose in the brain of anesthetized rats. Basal concentration was 1.5 +/- 0.1 mM (n = 3) and was decreased 60% by infusion of high-K(+) solution through the probe. These results demonstrate the potential of microdialysis with segmented flow to be used for in vivo monitoring experiments with high temporal resolution.     

A continuous film-recirculable drop gas-liquid equilibration device. Measurement of trace gaseous ammonia

A miniature gas-liquid equilibrator or a gas collector, intended as a low-volume interface between a soluble gaseous sample and a liquid phase analyzer or between a liquid phase sample and a detector designed for use with gas samples, is described. This paper addresses the application of the device for the measurement of trace atmospheric ammonia. Gas collection occurs solely by diffusive sampling such that aerosol particles are not collected. The device essentially consists of a tube surrounded externally by a jacket. Gas flows through the jacket and contacts a liquid film flowing on the surface of the tube. The flowing film forms a drop at the tube terminus and is aspirated off through the inner bore of the tube. The collected analyte can be (a) directly sent to an analysis system or (b) preconcentrated on a suitable stationary phase; the preconcentrator effluent can be recycled, if desired. With a fluorometric flow injection analysis system harnessed to measure ammonia with such a collector, the limit of detection (LOD, S/N = 3) for a sample drawn for 18 min at 200 mL/min was 4.5 parts per trillion by volume, with the linear range extending up to 30 parts per billion.     

严重段塞流引起的海洋立管振动响应

基于改进的严重段塞流瞬态数学模型和平面刚架理论,建立严重段塞流海洋立管耦合振动数学模型,对数学模型进行求解,研究了严重段塞流引起的海洋立管振动响应。数值模拟过程中,采用欧拉法计算严重段塞流流动参数,利用Galerkin法对立管结构动力学方程进行有限元离散,Newmark-β法求解离散方程。为了提高计算效率和精度,采用了变时间步长逐步积分方案。将数值模拟结果与实验数据进行对比,验证了数学模型和数值方法的准确性。对严重段塞流引起的立管系统位移响应、内力和支承力变化进行了深入分析。结果表明:立管系统的振动响应、内力变化规律与严重段塞流的周期性特征密切相关;弹性基础可以极大降低管道结构的振动幅度及内力,尤其是下倾管的弯曲内力;上升管的高频振动幅度较大,轴力和弯曲内力变化也较大。严重段塞流引起海洋立管振动响应的分析对海洋立管设计及其支承防护具有重要的指导意义。     

烟盒多层包装对水分阻隔影响研究

目的 卷烟包装的阻隔性能是卷烟产品品质稳定性的关键影响因素,研究干燥环境中卷烟多层包装对水分阻隔的作用。方法 利用自主研发测试系统——动态水分分析气候箱,考察不同盒包在特定温湿度条件下水分扩散过程,计算水分扩散通量,并对包装阻湿性能进行量化表征。结果 建立的烟盒多层包装水分阻隔性能评价方法可准确量化表征包装的阻湿性能。低湿条件下,水分从烟盒包装各层空隙及材料的透过量各有差异,对于Bopp膜,60%以上的水分主要从材料扩散,对于不同商标纸和内衬纸,水分从材料及空隙扩散的分配比不同。对于整体包装水分阻隔性能,三层材料中Bopp膜对烟支水分稳定性作用的占比达90%以上,硬包优于软包。准确预测了烟支在不同盒包中水分的散失速率,低湿条件下,硬包卷烟的水分散失速率明显低于软盒卷烟的。结语 文中建立了多层烟盒包装阻湿性测试及评价方法,量化表征了卷烟盒包各包装层及不同部位对水分的阻隔作用,明晰了烟盒包装中影响卷烟水分稳定性的重要因素。     

A photothermal interferometer for gas-phase ammonia detection

Detection of gas-phase ammonia is particularly challenging because ambient ammonia concentrations may be less than 1 ppb (molecules of NH(3) per 10(9) molecules of air), ammonia sticks to many materials commonly used to sample air, and particles containing ammonium may interfere with gas-phase measurements. We have built a new and sensitive photothermal interferometer to detect gas-phase ammonia in situ, under typical atmospheric conditions. Ammonia molecules in sampled air absorb infrared radiation from a CO(2) laser at 9.22 μm, with consequent collisional heating, expansion, and refractive index change. This change in refractive index is detected as a phase shift in one arm of a homodyne interferometer. Measurements of vibrational and electrical noise in the interferometer correlate to an instrumental lower limit of detection of 6.6 ppt ammonia in 1 s. The CO(2) laser output is modulated at 1.2 kHz, and the ac signal from the interferometer is measured with a lock-in amplifier. The detector is zeroed by sampling through a H(3)PO(4)-coated denuder tube and is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Signal gain is insensitive to CO(2) or H(2)O in the sample, and the signal is linear over 5 orders of magnitude. The instrument 2σ precision is 31 ppt when the signal is integrated for 100 s and 250 ppt with a 1-s integration time. The windowless sample cell and inlet is fabricated entirely of glass to minimize sample loss and hysteresis. The instrument response time is demonstrated to be about 1 s.     

Rapid and efficient detection of single chromophore molecules in aqueous solution

The first experiments on the detection of single fluorescent molecules in a flowing stream of an aqueous solution with high total efficiency are reported. A capillary injection system for sample delivery causes all the dye molecules to pass in a diffusion-broadened stream within a fast-moving sheath flow, through the center of the tightly focused laser excitation beam. Single-molecule detection with a transit time of ~1 ms is accomplished with a high-quantum-efficiency single-photon avalanche diode and a low dead-time time-gating circuit for discrimination of Raman-scattered light from the solvent.     

3-D velocity field measurement using multiple ultrasonic plane detections and high-order correlation analysis

A method of measuring the three-dimensional velocity field of laminarlike flow noninvasively by combining multiple ultrasonic plane detectors and a corresponding level of high-order cross-correlation analysis is presented. It is assumed that the velocity field consists of a set of straight line streams and that each stream contains random fluctuations that serve to tag the location of each stream as it passes through the detectors. The time delays of each stream between the various pairs of plane detectors are estimated by using high-order cross-correlation analysis of the detected signals. From the estimated time delays the stream velocities and their positions are measured and the three-dimensional velocity field pattern is reconstructed. To confirm the usefulness of this method, an actual measurement system has been constructed in a water tank, and experiments using controlled flow through thin tubes have been carried out. The details of the system and the results are shown.     

Chemiluminescent method for continuous monitoring of nitrous acid in ambient air

A continuous-flow method for measuring atmospheric HNO2 concentration in real time has been developed that uses a chemiluminescent NOx monitor. A Na2CO3 solution strips gaseous HNO2 from the atmosphere by means of pulling an air sample and the solution through a glass coil and mixing continuously with ascorbic acid solution which reduces nitrite to NO. The mixture is led into a gas-liquid separating coil consisting of microporous PTFE tubing. The NO evolved from the separating coil is swept out by a stream of clean air and detected with a chemiluminescent NOx monitor. The technique utilizes a dual flow system and dual channel NOx monitor to correct positive interferences from NO2 and peroxyacetyinitrate (PAN). The concentration of HNO2 is determined by difference between the two measurements. Sensitivity of the method is a function of the ratio of sampling flow rate to carrier gas flow rate, which permits readily a highly sensitive measurement.     

Evaluation of Permeability Through Permeation Experiments: Isostatic and Quasi-isostatic Methods Compared

Isostatic and quasi-isostatic permeation experiments were used to characterize the permeability of 1-hexanol through polypropylene films. The quasi- isostatic method was considered as an isostatic experiment at the limit a of null purging stream flow rate. Permeability values obtained through the isostatic method showed dependency on the purging stream flow rate. The extrapolated value at zero purging stream flow rate is in agreement with the data obtained via the quasi-isostatic procedure. Diffusion coefficient values were also determined. The isostatically obtained diffusion coefficients behave similarly to P. However, the value at zero flow rate differs significantly from the value obtained through the quasi-isostatic method. From these results the validity of permeation experiments for the evaluation of the diffusion coefficient is questioned.     

Sectional lumped parameter model using bond graph and simulation for hot asphalt pipelines

ABSTRACT

In order to achieve the matching control of hot asphalt and foaming water and improve the quality of foamed asphalt, fully considering the characteristics of the asphalt pipeline is necessary. Our dynamic model of the hot asphalt pipeline system was constructed by a sectional lumped parameter method, and the dynamic characteristics of the hot asphalt pipeline system were analyzed using Simulink software. The results showed that with decreasing pipe diameter and increasing pipe length and asphalt viscosity, the fluid pressure, flow vibration frequency, and amplitude reduced at the pipeline nozzle, whereas the loss increased. Under these conditions, the dynamic response of the pressure and flow reached the steady state faster. In contrast, with increasing pipe diameter and decreasing pipe length and asphalt viscosity, the fluid pressure, flow vibration frequency, and amplitude increased at the pipeline nozzle, whereas the loss decreased. The dynamic response speed of the pressure and flow attained steady state at a slower pace.     

Molecular Dynamics Simulation of Pervaporation of an Ethanol–Water Mixture on a Hybrid Silicon Oxide Membrane

A molecular-statistical method for simulating the process of pervaporation on hybrid silicon oxide membranes is proposed. This method is a development of the control volume method. Models of three membrane samples with different densities and pore sizes were obtained. These samples were used for the molecular-dynamics simulation of pervaporation of a 95 mol % aqueous solution of ethanol at a temperature of 343 K. It is shown that the membrane is selective with respect to water; the component flow is found to exponentially depend on the pore size.