Basic Principles and Modes of Capillary Electrophoresis
Harry Whatley
1. BASIC PRINCIPLES OF CAPILLARY ELECTROPHORESIS
1.1. Fundamentals of Electrophoresis
Capillary electrophoresis (CE) is a special technique that uses an electrical field in order to separate the components present in a mixture. Electrophoresis in a capillary can be differentiated from other types of electrophoresis that it is done within the walls of a narrow tube. To understand the functioning of molecules influenced by an electrical field inside a capillary it is important to know the phenomena that result from the geometry of a capillary.
1.1.1. Basic Principles
It has long been well known that molecules can possess positive or negative electrical charge. When the quantity
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Chromatographia 39, 391–404.
1.1.2.1. ADVANTAGES OF THE CAPILLARY
Introduction of capillaries into electrophoresis was as an anti-convective and heat controlling innovation. In wide tubes heat gradients leads to band mixing and resolution loss. The use of capillaries made of glass of 200–500-μm i.d. was reported by Virtanen (3) in 1969. Jorgensen’s (4) introduction of 75 μm capillary tubes was the beginning of new “high-performance” CE.
Figure 2 shows the separation of a mixture of two components (both
Of negative charge) in a capillary. A small plug of sample is introduced into one end. When an electrical field is on , the components start moving in the field as described previously. The narrow capillary decreases lateral diffusion and assures that temperature differences between the wall and the capillary center are quite small. Because these two components in this example travel at different velocities, they can separate. The geometry and other properties of the capillary electrophoretic separation also lead to a condition called plug flow. Under optimum plug flow conditions, diffusion is the only
Fig. 2. Capillary electrophoresis.
Factor that leads to sample dispersion. This makes separation of CE higher in