Electrophoresis mechanism

Interestingly, this equation indicates that the electrophoresis mechanism does not influence the enantioselectivity and the electric field only plays a role in driving the mobile phase. 

Electrophoretic deposition (EPD) is a wet electrolytic deposition technology for thin films. EPD employs the electrophoresis mechanism, as illustrated schematically in Fig. 1.11. The electric field is applied between two electrodes and charged particles dispersed or suspended in a liquid medium move toward the oppositely charged... 

Injecting the Sample The mechanism by which samples are introduced in capillary electrophoresis is quite different from that used in GC or HPLC. Two types of injection are commonly used hydrodynamic injection and electrokinetic injection. In both cases the capillary tube is filled with buffer solution. One end of the capillary tube is placed in the destination reservoir, and the other is placed in the sample vial. 

Behavior. Diffusion, Brownian motion, electrophoresis, osmosis, rheology, mechanics, and optical and electrical properties are among the general physical properties and phenomena that are primarily important in coUoidal systems (21,24—27). Of course, chemical reactivity and adsorption often play important, if not dominant, roles. Any physical and chemical feature may ultimately govern a specific industrial process and determine final product characteristics. 

Theory of Electrophoretic Motion. The study of the mechanics of electrophoresis focuses on the basis of electric potential on the surface of an object, and the relation of the electric potential to the velocity of the particle. Whereas research has been generally limited to nonmolecular particles of weU-defined geometry and is not strictly apphcable to molecules such as proteins and DNA fragments, this work is useful for understanding the physics of electrophoretic motion. 

Electroosmotic flow (EOE) is thus the mechanism by which liquids are moved from one end of the sepai ation capillai y to the other, obviating the need for mechanical pumps and valves. This makes this technique very amenable to miniaturization, as it is fai simpler to make an electrical contact to a chip via a wire immersed in a reservoir than to make a robust connection to a pump. More important, however, is that all the basic fluidic manipulations that a chemist requires for microchip electrophoresis, or any other liquid handling for that matter, have been adapted to electrokinetic microfluidic chips. 

The mechanism by which analytes are transported in a non-discriminate manner (i.e. via bulk flow) in an electrophoresis capillary is termed electroosmosis. Eigure 9.1 depicts the inside of a fused silica capillary and illustrates the source that supports electroosmotic flow. Adjacent to the negatively charged capillary wall are specifically adsorbed counterions, which make up the fairly immobile Stern layer. The excess ions just outside the Stern layer form the diffuse layer, which is mobile under the influence of an electric field. The substantial frictional forces between molecules in solution allow for the movement of the diffuse layer to pull the bulk... 

Enantioresolution in capillary electrophoresis (CE) is typically achieved with the help of chiral additives dissolved in the background electrolyte. A number of low as well as high molecular weight compounds such as proteins, antibiotics, crown ethers, and cyclodextrins have already been tested and optimized. Since the mechanism of retention and resolution remains ambiguous, the selection of an additive best suited for the specific separation relies on the one-at-a-time testing of each individual compound, a tedious process at best. Obviously, the use of a mixed library of chiral additives combined with an efficient deconvolution strategy has the potential to accelerate this selection. 

Guttman, A, On the Separation Mechanism of Capillary Sodium Dodecyl Sulfate-Gel Electrophoresis of Proteins, Electrophoresis 16, 611, 1995. 

Harrington, MG Lee, KH Bailey, JE Hood, LE, Sponge-Like Electrophoresis Media Mechanically Strong Materials Compatible with Organic Solvents, Polymer Solutions and Two-Dimensional Electrophoresis, Electrophoresis 15, 187, 1994. 

SaviUe, DA, The Eluid Mechanics of Continuous Elow Electrophoresis in Perspective, Physicochemical Hydrodynamics 1, 297, 1980. 

With the development of HPLC, a new dimension was added to the tools available for the study of natural products. HPLC is ideally suited to the analysis of non-volatile, sensitive compounds frequently found in biological systems. Unlike other available separation techniques such as TLC and electrophoresis, HPLC methods provide both qualitative and quantitative data and can be easily automated. The basis for the HPLC method for the PSP toxins was established in the late 1970 s when Buckley et al. (2) reported the post-column derivatization of the PSP toxins based on an alkaline oxidation reaction described by Bates and Rapoport (3). Based on this foundation, a series of investigations were conducted to develop a rapid, efficient HPLC method to detect the multiple toxins involved in PSP. Originally, a variety of silica-based, bonded stationary phases were utilized with a low-pressure post-column reaction system (PCRS) (4,5), Later, with improvements in toxin separation mechanisms and the utilization of a high efficiency PCRS, a... 

An example of a practical dielectrofilter which uses both of the features described, namely, sharp electrodes and dielectric field-warping filler materials, is that described in Fig. 20-33 [H. J. Hall and R. F. Brown, Lubric. Ens., 22, 488 (1966)]. It is intended for use with hydraulic fluids, fuel oils, lubricating oils, transformer oils, lubricants, and various refinery streams. Performance data are cited in Fig. 20-34. It must be remarked that in the opinion of Hall and Brown the action of the dielectrofilter was "electrostatic and due to free charge on the particles dispersed in the liquids. It is the present authors opinion, however, that both electrophoresis and dielectrophoresis are operative here but that the dominant mechanism is that of DEP, in which neutral particles are polarized and attracted to the regions of highest field intensity. 

Because HPLC and HPCE are based on different physico-chemical principles, HPCE may be expected to address areas in which HPLC has shortcomings [884]. One such area is time of separation. In terms of speed of analysis, selectivity, quantitation, methods to control separation mechanism, orthogonality, CE performs better than conventional electrophoresis and varies from HPLC (Table 4.49). CE has very high efficiency compared to HPLC (up to two orders of magnitude) or GC. For typical capillary dimensions 105—106 theoretical plates are common in CE compared to 20 000 for a conventional HPLC column and... 

Fig. 11-2. Schematic for preparative gel electrophoresis using a condenser for mechanical support and cooling.

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