High performance capillary electrophoresis - T.E.A.M.

Introduction
1.1 High performance
capillary
electrophoresis (CE)
– an overview
Capillary
Detector
Buffer Sample Buffer
HV
Electrode Electrode
Figure 1
Schematic of CE instrumentation
Separation by electrophoresis is obtained by differential
migration of solutes in an electric field. In CE, electrophoresis
is performed in narrow-bore capillaries, typically 25- to
75- µm inner diameter (id), which are usually filled only with
buffer. Use of the capillary has numerous advantages,
particularly with respect to the detrimental effects of Joule
heating. The high electrical resistance of the capillary
enables the application of very high electrical fields (100 to
500 V/cm) with only minimal heat generation. Moreover, the
large surface area-to-volume ratio of the capillary efficiently
dissipates the heat that is generated. The use of the high
electrical fields results in short analysis times and high
efficiency and resolution. Peak efficiency, often in excess of
10 5 theoretical plates, is due in part to the plug profile of the
electroosmotic flow, an electrophoretic phenomenon that
generates the bulk flow of solution within the capillary. This
flow also enables the simultaneous analysis of all solutes,
regardless of charge. In addition the numerous separation
modes which offer different separation mechanisms and
selectivities, minimal sample volume requirements (1 to
10 nl), on-capillary detection, and the potential for quantitative
analysis and automation, CE is rapidly becoming a
premier separation technique.
One key feature of CE is the overall simplicity of the instrumentation.
A schematic diagram of a generic capillary
electrophoresis system is shown in figure 1. Briefly, the ends
of a narrow-bore, fused silica capillary are placed in buffer
reservoirs. The content of the reservoirs is identical to that
within the capillary. The reservoirs also contain the electrodes
used to make electrical contact between the high
voltage power supply and capillary. Sample is loaded onto
the capillary by replacing one of the reservoirs (usually at
the anode) with a sample reservoir and applying either an
electric field or an external pressure. After replacing the
buffer reservoir, the electric field is applied and the separation
performed. Optical detection can be made at the
opposite end, directly through the capillary wall. The
theoretical and practical details regarding injection,
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