Isotachophoresis techniques

Electrodriven Separation Techniques encompass a wide range of analytical procedures based on several distinct physical and chemical principles, usually acting together to perform the requh ed separation. Example of electrophoretic-based techniques includes capillary zone electrophoresis (CZE), capillary isotachophoresis (CITP), and capillary gel electrophoresis (CGE) (45-47). Some other electrodriven separation techniques are based not only on electrophoretic principles but rather on chromatographic principles as well. Examples of the latter are micellar... 

Yamamoto et al. also coupled gel permeation HPLC and CE in an on-line fashion in 1990, where capillary isotachophoresis was again used in the second dimension. This technique was also not comprehensive due to the loss of resolution between the techniques. It was also not particularly fast, with a 23 min CE cycle, which was repeated 90 times throughout the HPLC run (14). Volume incompatibility between HPLC and CE was one problem not addressed in this study, in which a large HPLC column was coupled to an electrophoresis capillary. 

Capillary tube isotachophoresis using a potential gradient detector is another technique that has been applied to the analysis of alcohol sulfates, such as sodium and lithium alcohol sulfates [303]. The leading electrolyte solution is a mixture of methyl cyanate and aqueous histidine buffer containing calcium chloride. The terminating electrolyte solution is an aqueous solution of sodium octanoate. 

CE was recently used for anthocyanin analysis because of its excellent resolution. This technique has different modes capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), micellar electrokinetic chromatography (MEKC), capillary electrochromatography (CEC), capillary isoelectric focusing (CIEE), and capillary isotachophoresis (CITP)."° CZE is the most popular method for anthocyanin... 

There are a few other analytical methods in which electrochemistry plays an essential role, such as (paper) electrophoresis, isotachophoresis, electrography and electrochromatography (according to Fujinaga) as they belong to analytical separation techniques, they are beyond the scope of this book. 

One of the major advantages of CE as a separation technique is the wide variety of separation modes available. Analytes can be separated on the basis of charge, molecular size or shape, pi, or hydrophobicity. The same CE instrument can be used for zone electrophoresis, IEF, sieving separations, isotachophoresis, and chromatographic techniques such as MEKC and capillary electrokinetic chromatography. This section provides a brief description of each separation mode. Zone electrophoresis, IEF, and sieving are the primary modes used for protein separations, and these will be discussed in detail in the following sections. 

Several strategies have been described for the preconcentration of sample components present at low concentrations. These techniques include zone sharpening,28-29 on-line packed columns,30 and transient capillary isotachophoresis (cITP).31-32 Other standard laboratory techniques are often used, including solid-phase extraction, protein precipitation, ultrafiltration, etc. Two important points to keep in mind when selecting a concentration protocol are the sample requirements of the method and the potential selectivity on relative concentrations of sample components. The latter point applies to purity and concentration analysis. 

The hyphenation of CE and NMR combines a powerful separation technique with an information-rich detection method. Although compared with LC-NMR, CE-NMR is still in its infancy it has the potential to impact a variety of applications in pharmaceutical, food chemistry, forensics, environmental, and natural products analysis because of the high information content and low sample requirements of this method [82-84]. In addition to standard capillary electrophoresis separations, two CE variants have become increasingly important in CE-NMR, capillary electrochromatography and capillary isotachophoresis, both of which will be described later in this section. 

Capillary isotachophoresis (CITP) is an electromigration technique, which is performed using a discontinnous buffer system, formed by a leading electrolyte (LE) and a terminating electrolyte... 

Electrophoresis is one of many electromigrational separation techniques which include isotachophoresis, immunoelectrophoresis and isoelectric focussing that have been used to separate various species on the basis of their different mobility in an electric field. These techniques can be used not only to achieve separations but also it is possible to identify the ligand bound to the metal. This can be done by comparing the isoelectric points, immunological behaviours, extent of mobilities or step heights of the sample constituents with those of well-characterised standards. A difficulty, however, is in the determination of the metal constituent itself. Except in the case of radioisotopes, the activities of which can be easily measured, non-radioactive elements can be detected only after further separation steps. 

Because of the use of various electrolyte systems, pH gradients, and not least an electric field, some complexes would not survive the separation. It is therefore necessary that the species to be separated are both thermodynamically and kineti-cally stable. Recently, Bocek and Foret have reviewed the application of isotachophoresis to the separation of inorganic species. This technique appears to be well-suited for the study of the distribution of metabolites of metal-containing drugs in body fluids. A survey of the application of electrophoretic techniques to biological materials can be found in the book edited by Deyl... 

In 1989, Yamamoto et al. developed the first technique that directly coupled chromatography to capillary electrophoresis, although again in a non-comprehensive fashion. Low-pressure gel permeation chromatography, which separates analytes based on differences in molecular size, was combined with capillary isotachophore-sis, which separates according to electrophoretic mobility. Capillary isotachophoresis... 

The development of electrophoretic techniques afforded possibilities for fractionations based on charge density differences. Duxbury (1989) has reviewed applications of different electrophoretic separation methods, including zone electrophoresis, moving boundary electrophoresis, isotachophoresis, and isoelectric focusing (IEF). Preparative column electrophoresis (Clapp, 1957) and continuous flow paper electrophoresis (Hayes, 1960 summarized by Hayes et al., 1985) methods have been used to separate components isolated from sapric histosol soils. These techniques allowed separation of polysaccharides from the colored components the electrophoretograms of the colored components were diffuse, showing a continuum of components of different charge densities. 

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