An Overview of Electrophoresis

Electrophoresis on a macro scale has been applied to a variety of difficult analytical separation problems inorganic anions and cations, amino acids, catecholamines. drugs, vitamins, carbohydrates, peptides, proteins, nucleic acids, nucleotides, polynucleotides, and numerous other species. 

An electrophoretic separation is performed by injecting a small band of the sample into an aqueous butler solution contained in a narrow tube or on a flat porous support medium such as paper or a semisolid gel. A high voltage is applied across the lenulh of the buffer by means of a pair of electrodes located at each 

FIGURE 30-1 Schematic of a capillary eleclro-phoresis system. 

Electrophoretic separations are currently performed in two quite different formats one is called slab electrophoresis and the other capillary electrophoresis. The first is the classical method ihal has been used for many years to separate complex, high-molecular-mass species of biological and biochemical interest. Slab separations arc carried out on a thin flat layer or slab of a porous semisolid gel containing an aqueous buffer solution within its pores. This slab has dimensions of a few centimeters on a side and, like a chromatographic thin-layer plate, is capable of separating several samples simultaneously. Samples arc introduced as spots or bands on the slab, and a dc electric held is applied across the slab for a fixed period. When the separations are complete, the Held is discontinued and the separated species are visualized by staining in much the same way as was described for thin-layer chromatography in Section 281-2, 

Slab electrophoresis is now the most widely used separation tool in biochemistry and biology. Monographs, textbooks, and journals in the life sciences contain hundreds of photographs of developed electrophoretic slabs. Capillary electrophoresis. which is ail instrumental version of electrophoresis, was developed in the mid-to-latc 1980s. It has become an important tool for a wide variety of analytical separation problems. In many cases, this new method of performing electrophoretic separations is a satisfactory substitute for slab electrophoresis with several important advantages that are descril ed later in this chapter. 

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A An Overview of Electrophoresis 867 30B Capillary Electrophoresis 868 30C Applications of CE 875 30D Packed Column Electrochromatography 30E Field-Flow Fractionation 884 Questions and Problems 888... 

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