High performance capillary electrophoresis electrolytes

One variant of absorbance detection that is widely used in HPLC can also be used in high performance capillary electrophoresis. For compounds that exhibit a very weak UV absorption, buffers such as chromate or phthalate, which have high absorption properties, can be used. Under these experimental conditions, the UV absorbance diminishes as analytes flow past the detector (due to the dilution effect of the electrolyte). This leads to negative peaks on the recorder (see Fig. 8.9). 

The solution contained within the capillary in which the separation occurs is known as the background electrolyte (BGE), carrier electrolyte, or, simply, the buffer. The BGE always contains a buffer because pH control is the most important parameter in electrophoresis. The pH may affect the charge and thus the mobility of an ionizable solute. The electro-osmotic flow (EOF) is also affected by the buffer pH. Table 1 contains a list of buffers that may prove useful in high-performance capillary electrophoresis (HPCE). As will be seen later, only a few of these buffers are necessary for most separations. 

Huber, C.G., Premstaller, A. (1999). Evaluation of volatile eluents and electrolytes for high-performance liquid chromatography-electrospray ionization mass spectrometry and capillary electrophoresis-electrospray ionization mass spectrometry of proteins. I. Liquid chromatography. J. Chromatogr. A 849, 161-173. 

The method of complete electrolysis is also important in elucidating the mechanism of an electrode reaction. Usually, the substance under study is completely electrolyzed at a controlled potential and the products are identified and determined by appropriate methods, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis. In the GC method, the products are often identified and determined by the standard addition method. If the standard addition method is not applicable, however, other identification/determination techniques such as GC-MS should be used. The HPLC method is convenient when the product is thermally unstable or difficult to vaporize. HPLC instruments equipped with a high-sensitivity UV detector are the most popular, but a more sophisticated system like LC-MS may also be employed. In some cases, the products are separated from the solvent-supporting electrolyte system by such processes as vaporization, extraction and precipitation. If the products need to be collected separately, a preparative chromatographic method is use-... 

Lately, IL-based surfactants have been used in separation techniques of wide apph-cability, such as high-performance hqnid ehromatography (HPLC) and capillary electrophoresis (CE). This section will only focus on those applications that take advantages of the micellar properties of IL-based sinfactants, that is, works that use micellar solutions of IL-based surfactants in HPLC or in CE. In this consideration, applications that employ IL-based surfactant as mere background electrolytes have not been taken into account. 

To analyze the aqueous phase for any of these substances, it must first be separated from the polymer particles. Both flocculation and membrane filtration techniques can be used for this purpose and they are described in more detail below. The detection of the substances listed above can then be performed with the usual array of analytical methods used for characterizing aqueous media. For the determination of emulsifiers, electrolytes and water-soluble monomers, ion chromatography (IC) and high-performance liquid chromatography (HPLC) are particularly suitable. The techniques of choice for characterizing oligomers are gel permeation chromatography (GPC) and capillary electrophoresis (CE). As these analytical techniques are not specific to colloidal chemistry, they will not be described further here and the reader should consult the literature for more information. 

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