Study of sample dispersionin flow injection analysis

doi:10.1016/S0003-2670(00)80433-X

Analytica Chimica Acta

Volume 214, 1988, Pages 97-105

https://doi.org/10.1016/S0003-2670(00)80433-X Get rights and content

Abstract

Specially designed appratus is described for studying the dispersion behavior of sample zones injected into poly (tetrafluoroethylene) tubing (0.5–1 mm i.d.). microscope and photometric detection is used. Evaluation of the photographic data and photometric response curves indicates that thinner, narrower tubes effectively improve sensitivity, slow flow rates promote the mixing cause by molecular diffusion, and coiling of the tubing reduces axial dispersion.

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Use of small reactors implies, however, on difficulties in getting similar linear velocities for all the involved fluid elements, as a laminar flow regime is inherent to flow analysis. Under these conditions, the fluid elements at the central portion of the flowing stream travel at a velocity nearly twice the average, whereas the velocities of the fluid elements near the tubing wall approach zero [43]. With fluid elements at so different linear flow velocities, the critical velocity value associated with the fluidization point (Fig. 2) is not easily achieved with ordinary sample propelling devices, such as peristaltic, piston or syringe pumps.
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Environmental Monitoring
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In the field of analytical chemistry and its instrumentation, microsystem technology has been most remarkable, because it leads to on-site and real-time monitoring, high-speed and high-throughput analysis, resulting from a small sample volume, rapid operation procedure, and a small measuring device space. Although the atmospheric environment has a lot of pollutants, few researches deal with the gas phase as most of these researches have been proposed for analyzing liquid samples. Because of significant differences between the physical parameters of gas and liquid phases, such as viscosity and compressibility, the control of a stable gas–liquid equilibrium system in a microchannel is relatively difficult. If the chemicals in the environment can be easily taken into microsystems, their application to sample pretreatment microchips and downsized mass spectrometer systems will diversify further. After analyzing the simple gas–liquid equilibrium system on a microchip, for example, a gas–liquid contacting pretreatment microsystems via porous material was described, and several novel gas, liquid, and solid sample pretreatment methods were developed by utilizing mass transfer microsystems from gas, liquid, and solid phases, respectively, to the liquid phase.
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Random walk simulation of flow injection analysis. Evaluation of dispersion profiles
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The use of the random walk model for simulating peak shapes in flow injection analysis (FIA) is investigated. Studies are limited to the case of dispersion in straight tubes with laminar flow (no reaction), but more precise peak shape data than has previously been available is provided. Peak shapes obtained with the random walk model are compared with experimental results and predictions made by other theoretical approaches. Comparisons utilize a wide variety of conditions, including those treated by other authors. Favourable agreement is obtained in all cases, although some differences with experimental results are observed. The computational aspects of the random walk algorithm are considered and guidelines for its implementation are provided. The versatility of the algorithm is demonstrated through the presentation of simulation results for modified laminar flow profiles, asymmetric flow profiles, and conditions of infinite radial diffusion.
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Solute dispersion of an injected sample plug was studied by using an experimental apparatus with ideal laminar flow in order to develop a hydrodynamic model for the design of sensitive and precise flow-injection analysis systems. The dispersion behaviour of the sample slug under different manifold conditions was first studied in detail to evaluate the effects of various operating conditions such as tube radius, tube length, flow-rate and molecular diffusion coefficient of sample solute. The capillary flow properties were also examined for some commercial micropumps to select the most suitable pumping method. Mixing profiles and baseline stability in short, straight tubes were investigated. A double-plunger micropump having a linear can mechanism and a fast, short reciprocation time was proposed to obtain smoother mixing and more stable pumping with good reproducibility. Complete mixing and low flow-rate pumping are strongly desired for reliable flow-injection methods for industrial process use; biosensing devices for protein and enzyme bioassays require lower consumption of valuable reagents.

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Study of sample dispersionin flow injection analysis

Abstract

Talanta

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

Talanta

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta