Reduction in sample injection bias using pressure gradients generated on chip

Sample injection in microchip-based capillary zone electrophoresis (CZE) frequently rely on the use of electric fields which can introduce differences in the injected volume for the various analytes depending on their electrophoretic mobilities and molecular diffusivities. While such injection biases may be minimized by employing hydrodynamic flows during the injection process, this approach typically requires excellent dynamic control over the pressure gradients applied within a microfluidic network. The current article describes a microchip device that offers this needed control by generating pressure gradients on-chip via electrokinetic means to minimize the dead volume in the system. In order to realize the desired pressure-generation capability, an electric field was applied across two channel segments of different depths to produce a mismatch in the electroosmotic flow rate at their junction. The resulting pressure-driven flow was then utilized to introduce sample zones into a CZE channel with minimal injection bias. The reported injection strategy allowed the introduction of narrow sample plugs with spatial standard deviations down to about 45 μm. This injection technique was later integrated to a capillary zone electrophoresis process for analyzing amino acid samples yielding separation resolutions of about 4–6 for the analyte peaks in a 3 cm long analysis channel.     

流动注射化学发光法测定氨基硫脲

基于氨基硫脲对高锰酸钾-乙二醛化学发光体系的增敏作用,建立了氨基硫脲的流动注射化学发光测定方法;在最佳测试条件下,氨基硫脲的检出限为5.0×10-8mol·L-1,线性范围为1.0×10-7-1.0× 10-3mol·L-1;对1.o×10-6mol·L-1的氨基硫脲溶液平行测定11次,其RSD为2.1%.该方法可应用...     

流动注射共振光散射法测定维生素C

建立了测定维生素C的流动注射共振光散射分析新方法.在弱酸介质中,利用维生素C将Cu2+还原成Cu+,Cu+进-步与SCN-生成CuSCN沉淀颗粒,用流动注射共振光散射法间接测定维生素C.测定的维生素C线性范围为1.0-120.0mg/L,检出限为0.84mg/L.所建立的分析方法简便、所用试剂少、线性范围宽,可用于饮料...     

Experimental and analytical investigation of liquid sheet breakup characteristics

The main objective of this research is to study analytically and experimentally the liquid sheet breakup of a flat fan jet nozzle resulting from pressure-swirling. In this study the effects of nozzle shape and spray pressure on the liquid sheet characteristics were investigated for four nozzles with different exit widths (1.0, 1.5, 2.0 and 2.5 mm). The length of liquid sheet breakup, liquid sheet velocity and the size of formed droplets were measured by a digital high speed camera. The breakup characteristics of plane liquid sheets in atmosphere are analytically investigated by means of linear and nonlinear hydrodynamic instability analyses. The liquid sheet breakup process was studied for initial sinuous and also varicose modes of disturbance. The results presented the effect of the nozzle width and the spray pressure on the breakup length and also on the size of the formed droplets. Comparing the experimental results with the theoretical ones for all the four types of nozzles, gives a good agreement with difference ranges from 4% to 12%. Also, the comparison between the obtained results and the results due to others shows a good agreement with difference ranged from 5% to 16%. Empirical correlations have been deduced describing the relation between the liquid sheet breakup characteristics and affecting parameters; liquid sheet Reynolds number, Weber number and the nozzle width.     

跨音速湿空气非平衡凝结流动的数值研究

跨音速流动条件下湿空气中的水蒸气由于快速膨胀而发生非平衡凝结,凝结潜热对跨音速气流进行加热,会显著改变气流的流动特性。通过对商用计算流体动力学软件FLUENT进行二次开发,建立了湿空气非平衡凝结流动的数值求解方法。该方法可用于二维或三维、粘性或无粘、内流或外流的求解中。采用该方法分剐对缩放喷管、透平叶栅以及绕CA-0.1圆弧翼型的湿空气非平衡凝结流动进行了数值分析。计算结果表明：湿空气凝结手l起缩放喷管中的凝结激波、导致叶橱流动中总压降低;对于翼型周围的流动,在相对湿度分别为50％、57．1％、64.1％时,依次计算得到了单激波、五激波、双激波。     

Injection profiles in liquid chromatography II: predicting accurate injection-profiles for computer-assisted preparative optimizations

In computer assisted optimization of liquid chromatography it has been known for some years that it is important to use experimental injection profiles, instead of rectangular ones, in order to calculate accurate elution bands. However, the incorrectly assumed rectangular profiles are still mostly used especially in numerical optimizations. The reason is that the acquisition of injection profiles, for each injection volume and each flow rate considered in a computer-assisted optimization requires a too large number of experiments. In this article a new function is proposed, which enables highly accurate predictions of the injection profiles and thus more accurate computer optimizations, with a minimum experimental effort. To model the injection profiles for any injection volume at a constant flow rate, as few as two experimental injection profiles are required. If it is desirable to also take the effect of flow rate on the injection profiles into account, then just two additional experiments are required. The overlap between fitted and experimental injection profiles at different flow rates and different injection volumes were excellent, more than 90%, using experimental injection profiles from just four different injection volumes at two different flow rates. Moreover, it was demonstrated that the flow rate has a minor influence on the injection profiles and that the injection volume is the main parameter that needs to be accounted for.     

Topological and thermodynamic investigations of ternary mixtures containing cyclic ether: Excess molar enthalpies

Excess molar enthalpies, H_ijk^E, of 1,3-dioxolane or 1,4-dioxane (i) + aniline (j) + benzene or toluene (k) ternary mixtures have been measured as a function of composition at 308.15 K. The H_ijk^E data have been fitted to Redlich-Kister equation to determine ternary adjustable parameters along with their standard deviations. It has been observed that H_ijk^E values predicted by Graph theory compare well with their corresponding experimental values. The observed data have been analyzed in terms of (i) Graph theory (which involves the topology of a molecule); (ii) Prigogine-Flory-Patterson; and (iii) Sanchez and Lacombe theories.     

Oscillatory shear-accelerated exfoliation of graphite in polypropylene melt during injection molding

In this study, good dispersion status of graphite in a nonpolar, intractable polymer, i.e. polypropylene (PP), was realized in melt processing by using a specific dynamic packing injection molding (DPIM) technique. The exfoliation extent of graphite increased remarkably from the skin zone to the core zone of the molded part, as confirmed by combination of WAXD, SEM and TEM analyses, indicating an accelerated exfoliation occurred during the DPIM processing. This phenomenon is due to decreased melt flow channel and increased melt viscosity as the solidification takes place from the wall into the center, which leads to greatly increased shear force. The good dispersion of graphite results in obvious reinforcements of both tensile strength and impact strength by adding moderate amount of graphite. The present study proposes a promising route for realizing the large-scale fabrication of structural parts of polymer/exfoliated-graphite nanocomposites with excellent mechanical properties.     

Experimental study of the influence of annular nozzle on acoustic characteristics of detonation sound wave generated by pulse detonation engine

Acoustic characteristics of the detonation sound wave generated by a pulse detonation engine with an annular nozzle, including peak sound pressure, directivity, and A duration, are experimentally investigated while utilizing gasoline as fuel and oxygen-enriched air as oxidizer. Three annular nozzle geometries are evaluated by varying the ratio of inner cone diameter to detonation tube exit diameter from 0.36 to 0.68. The experimental results show that the annular nozzles have a significant effect on the acoustic characteristics of the detonation sound wave. The annular nozzles can amplify the peak sound pressure of the detonation sound wave at 90° while reducing it at 0° and 30°. The directivity angle of the detonation sound wave is changed by annular nozzles from 30° to 90°. The A duration of the detonation sound wave at 90° is also increased by the annular nozzles. These changes indicate that the annular nozzles have an important influence on the acoustic energy distribution of the detonation sound wave, which amplify the acoustic energy in a direction perpendicular to the tube axis and weaken it along the direction of the tube axis.     

Effects of reprocessing on the structure and properties of polyamide 6 nanocomposites

PA6 based nanocomposites (NCs) were reprocessed by repeated injection moulding to find out whether reprocessing is possible in these materials by means of the observation of the changes in the structure and mechanical properties. The studied variables were (a) the number of cycles (1-5), (b) the origin of the NC: either laboratory mixed or commercial and (c) the processing temperature (230 °C and 270 °C). Neat PA6 was also reprocessed as a reference material. In spite of the colour change, the Young's modulus, the solid state characteristics and the dispersion level were preserved upon reprocessing. The lack of change of chemical nature observed by FTIR, and the observed decreases in viscosity indicated that the main effect of reprocessing was a decrease in the molecular weight. At 230 °C the decreases in viscosity were smaller after reprocessing, and almost no change was seen in the structural parameters and properties. The decrease in the molecular weight after reprocessing at 270 °C leads to lower ductility and mainly to a decrease in the ability of the nPA6 matrix to cold draw. However, no change of the interphase conditions or agglomeration of the OMMT was detected and the NCs remained clearly ductile; thus, revealing a lack of deterioration of the interface and the ability of the NCs for recycling.