Electrokinetics disadvantages

There are two main injection strategies for CE, electrokinetic and pressure. Each type of injection mode has its advantages and disadvantages. Depending on the application, the appropriate mode must be chosen. 

The use of centrifugation to separate the liquid from solid phases in traditional batch or tube techniques has several disadvantages. Centrifugation could create electrokinetic effects close to soil constituent surfaces that would alter the ion distribution (van Olphen, 1977). Additionally, unless filtration is used, centrifugation may require up to 5 min to separate the solid from the liquid phases. Many reactions on soil constituents are complete by this time or less (Harter and Lehmann, 1983 Jardine and Sparks, 1984 Sparks, 1985). For example, many ion exchange reactions on organic matter and clay minerals are complete after a few minutes, or even seconds (Sparks, 1986). Moreover, some reactions involving metal adsorption on oxides are too rapid to be observed with any batch or, for that matter, flow technique. For these reactions, one must employ one of the rapid kinetic techniques discussed in Chapter 4. 

The introduction of the samples onto the capillary column can be carried out by either displacement techniques or electrokinetic migration. Three methods of displacement or hydrostatic injection are available a) direct injection, or pressure b) gravity flow, or siphoning and c) suction. The electrokinetic injection method arose from findings that electroosmosis act like a pump (80). Both methods have advantages and disadvantages. For example, a bias has been reported in electrokinetically injected... 

To a large extent, these disadvantages are offset by the possibility of obtaining additional information that is difficult to obtain for mercury, such as electroklnetic potentials, colloid stability data and directly measured adsorptions. Even in cases where the evaluation and interpretation of i -potentlals from electrokinetics are under discussion, the technique is powerful because it informs us about the sign of the diffuse part of the double layer and hence helps to detect (super-)equivalency of specific adsorption. Quantitative information on specific adsorption can also be obtained by comparing p.z.c. s and l.e.p. s. Because of all of this, over the past decades systematic studies on a number of well-characterized disperse systems have led to a number of qualitatively new features, whereas the progress in the domain of mercury double layers has been rather quantitative. 

In most electroosmotic flows in microchannels, the flow rates are very small (e.g., 0.1 pL/min.) and the size of the microchannels is very small (e.g., 10 100 jm), it is extremely difficult to measure directly the flow rate or velocity of the electroosmotic flow in microchannels. To study liquid flow in microchannels, various microflow visualization methods have evolved. Micro particle image velocimetry (microPIV) is a method that was adapted from well-developed PIV techniques for flows in macro-sized systems [18-22]. In the microPIV technique, the fluid motion is inferred from the motion of sub-micron tracer particles. To eliminate the effect of Brownian motion, temporal or spatial averaging must be employed. Particle affinities for other particles, channel walls, and free surfaces must also be considered. In electrokinetic flows, the electrophoretic motion of the tracer particles (relative to the bulk flow) is an additional consideration that must be taken. These are the disadvantages of the microPIV technique. 

Electrokinetics is a very effective technique to transport nitrate and fluoride, although the transport characteristics of anionic contaminants such as nitrate and fluoride are quite different from the transport of cationic metals. In electrokinetic restoration of saline soil, the electrokinetic transport of cationic salts, as well as nitrates, should be considered. Changes in pH near electrodes after electrokinetic treatment of saline soil are the disadvantages of electrokinetic restoration however. 

Though electrokinetics is being advocated as an effective treatment mechanism, a lot of process-related issues, such as its ability to achieve the remediation goals, are yet to be addressed. Some of the major disadvantages of the technology are... 

This document is organized in the following manner first, a brief introduction to the electric double layer and its significance to electrokinetic phenomenon. Second, the principles behind zeta potential measurements based on the three types of electrokinetic phenomenon are discussed, with special attention to the advantages and disadvantages of each method. Finally, a few key research results for each of the methods are presented. The purpose of this entry is to provide the reader with a brief introduction to the fundamentals of zeta potential measurements for a more detailed description of zeta potential measurements, electric double layer, and electrokinetic phenomenon, the reader should consult the various texts that discuss these topics in depth [1—4]. 

Another method for the determination of electrophoretic mobility which has emerged in recent years is that of the measurement of the electrokinetic sonic amplitude (ESA) for a particle subjected to an alternating current (8). This electroacoustic effect is a result of the oscillation of the particles near the electrodes where a sound wave is produced that can be picked up by a pressure transducer located behind the electrode. The ESA pressure signal is simultaneously proportional to the dynamic mobility of the particle, the particle volume fraction and the density difference between particle and solvent. Thus, the electroacoustic effect is appropriate for concentrated dispersions where conventional electrophoretic methods are inappropriate. However, one disadvantage of the method is that it is not appropriate to systems having low density differences between the particles and suspending liquid. 

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