Differential migration

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

Zone electrophoresis is defined as the differential migration of a molecule having a net charge through a medium under the influence of an electric field (1). This technique was first used in the 1930s, when it was discovered that moving boundary electrophoresis yielded incomplete separations of analytes (2). The separations were incomplete due to Joule heating within the system, which caused convection which was detrimental to the separation. 

The basis of chromatography is in the differential migration of chemicals injected into a column. The carrier fluid takes the solutes through the bed used for elution (mobile phase). The bed is the stationary phase. Based on mobility, the retention-time detectors identify the fast and slow-moving molecules. Based on internal or external standards with defined concentration, all unknown molecules are calculated in a developed method by software. GC columns are installed in an oven which operates at a specified temperature. A diagram of an oven with GC column is shown in Figure 7.16. 

Development in TLC is the process by idiich the mobile phase moves through the sorbent layer, thereby inducing differential migration of the suple components. The principal development modes used in TLC are linear, circular and anticircular with the velocity of the mobile phase controlled by capillary forces or forced-flow conditions. In any of these modes the development process can be extended by using continuous development or multiple development. 

Martinez-Marcos A., Ubeda-Banon I. and Halpem M. (2000). Cell turnover in the vomeronasal epithelium evidence for differential migration and maturation of subclasses of vomeronasal neurons in the adult opossum. J Neurobiol 43, 50-63. 

Tissues consist of smaller repeating units on the scale of hundreds of micrometers in vivo. The 3D architecture of these repeating tissue units underlies the coordination of multicellular processes, emergent mechanical properties, and integration with other organ systems via the microcirculation [11], Furthermore, the local cellular environment presents biochemical, cellular, and physical stimuli that orchestrate cellular fate processes such as proliferation, differentiation, migration, and apoptosis. Thus, successful fabrication of a fully functional tissue must include both an appropriate environment for cell viability and function at the microscale... 

The principal analytical methods for complex samples are those that separate the mixture by differential migration and then detect the separated components. The separation methods are chromatography, electrophoresis, and field flow fractionation the detection methods—which need not be selective but must be sensitive—include absorption, laser-induced fluorescence, electrochemistry, and mass... 

Separation mainly of charged materials by differential migration across a surface or through a column in an applied potential gradient migration rates dependent upon size, shape and charge of species. 

Traditional electrophoresis involves the differential migration of charged species in an electrolyte solution under the influence of an applied potential gradient. The rate of migration of each species is a function of its charge, shape and size. In traditional zone electrophoresis, the electrolyte solution is retained by an inert porous supporting medium, usually paper or gel, in the form of a sheet or column. Application of a dc potential across the solution for a period of time results in the components of a mixture, originally placed... 

The difference in movement rates of various compounds through a column is attributed to differential migration in HPLC. This can be related to the equilibrium distribution of different compounds such as X, Y, and Z between the stationary phase and the flowing solvent(s), or mobile phase. The speed with which each compound moves through the column (ux) is determined by the number of molecules of that compound in the moving phase, at any moment, since sample molecules do not move through the column while they are in the stationary phase. The molecules of the solvent or mobile phase move at the fastest possible rate except in size exclusion chromatography, where molecular... 

E. Heftmann, Chromatography, fundamentals and applications of chromatography and related differential migration methods, Part A- Fundamentals and Techniques, 5th ed., Elsevier, Amsterdam, 1992. 

Proteins contain a variety of functional groups and interact with the stationary phase at a number of simultaneous sites on the protein molecule, each more or less affected by change in eluent, or mobile-phase, pH or ionic strength. The equilibrium constant for the dissociation of the adsorption complex thus contains a product of many eluent-sensitive concentration terms, and the equilibrium position is very sensitive to elution conditions. Under the elution conditions, some proteins in a mixture may be tightly bound by the stationary phase (t), oo) while others are unretained (t R 0). Differential migration (Section 19.2.1) is replaced by extreme retention values. 

For separation, analytes must be retained and have differential migration in the column Separation of components cannot occur without retention and interaction with the stationary phase. In addition, analytes must show differential retention vs. other components. 

Electrophoresis is a separation technique that is based on the differential migration of charged compounds in a semi-conductive medium under the influence of an electric field. Its origin can be traced back to the 1880s however, it got major recognition in 1937, when Arne... 

CZE is the basic technique of the free solution method in CE. Separation of components is achieved due to a differential migration caused by differences in effective mobilities. The... 

Heftmann, E. (1992). Chromatography Fundamentals and Applications of Chromatography and Related Differential Migration Methods, Part A Fundamentals and Techniques, 5th Edition, Elsevier Science, Amsterdam. 

Since CEC is a hybrid technique, the differential migration of analytes through the stationary phase bed will generally involve lipophilic, electrostatic, and electrophoretic processes between the analytes and the stationary and mobile phases. Consequently, the applied voltage and electrical field strength and the mobile phase properties such as pH, buffer concentration, ionic strength, temperature, and the organic content will all affect the separation. For a detailed discussion, also refer to reference 10. 

A variety of microscale separation methods, performed in capillary format, employ a pool of techniqnes based on the differential migration velocities of analytes under the action of an electric field, which is referred to as capillary electromigration techniques. These separation techniques may depend on electrophoresis, the transport of charged species through a medium by an applied electric field, or may rely on electrically driven mobile phases to provide a true chromatographic separation system. Therefore, the electric field may either cause the separation mechanism or just promote the flow of a solution throughout the capillary tube, in which the separation takes place, or both. 

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