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

Instrumentation/Operation
T, ˚C
100
80
60
40
20
0 5 10 15 20 25 30 35
V, kV
Figure 54
Estimated temperature of sample zone
and running buffer under stacking
conditions 30
closed symbols = sample zone
open symbols = buffer
Conditions: 10 mM tricine, pH 8.0,
containing 0 mM NaCl (circles)
25 mM NaCl (squares)
50 mM NaCl (triangles)
results in zone broadening. Optimal stacking is obtained
when the running buffer concentration is about 10 times of
the sample and when the plug length is up to 10 times the
diffusion-limited peak width.
One further consideration in the use of stacking during
injection is the generation of heat in the sample zone.
Under typical stacking conditions most of the voltage drop
occurs in the stacking zone. The corresponding power
generation can result in significantly elevated temperatures.
In fact, temperatures exceeding 90 °C in the sample
zone, even with capillary thermostating, have been reported
(figure 54). This can be of particular concern for thermally
labile samples.
4.2 Separation
The separation step in the CE experiment includes the
following components: the capillary, capillary thermostating
system, and power supply. Each is described in
the following sub-sections, with emphasis on aspects of
migration time/mobility reproducibility.
4.2.1 Capillary
Ideal properties of the capillary material include being
chemically and electrically inert, UV-Visible transparent
flexible and robust, and inexpensive. Meeting most of these
requirements, fused silica is the primary material employed
today. Fused silica has been used in applications such
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