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

Batch-to-batch reproducibility is highly dependent on the
nature of the fused silica itself. Surface charge and EOF can
vary 5 % RSD or more between capillary batches. Comparison
of inter-capillary data often requires normalization of
EOF.
4.2.2 Capillary thermostating
Effective control of capillary temperature is important for
reproducible operation. Temperature regulation to ± 0.1 °C
is beneficial due to the strong viscosity dependence of
sample injection and migration time. Further, the system
should isolate the capillary from changes in ambient
temperature. The two approaches generally used are to bath
the capillary in a high velocity air stream or in a liquid.
While liquid thermostating is theoretically more efficient,
forced air thermostating at º 10 m/s air velocity is usually
sufficient for the quantity of heat generated in CE. As
shown in the Ohm’s law plots of figure 14, efficiency of the
two systems is similar up to about 5 W/m. Although the
liquid system is more effective at higher power generation,
CE experiments are not usually performed under such
conditions. A benefit of the air thermostating system is
instrumental simplicity and ease of use.
Instrumentation/Operation
4.2.3 High voltage power supply
In CE a DC power supply is used to apply up to about 30 kV
and current levels of 200 to 300 mA. Stable regulation of the
voltage (± 0.1 %) is required to maintain high migration time
reproducibility.
The power supply should have the capability to switch
polarity. Under normal conditions the EOF is in the direction
of the cathode. In this case, injection is made at the
anode.
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