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

Instrumentation/Operation
Diode-array
detector
Vial
carousel
(thermostatted)
HV
Capillary
thermostatting
Buffer replenishment
Figure 49
Schematic of CE instrumentation
This chapter describes the instrumental and experimental
aspects of CE. In order to facilitate the discussion, the
Agilent CE system will be used as an example. However,
most instrumental aspects are described generically and
need not be specific to this instrument.
The basic instrumental design is shown schematically in
figure 49. A typical CE experiment, performed by these
Integrated components, involves a series of steps: 1)
removal of the inlet buffer reservoir and replacing it with
sample vial; 2) loading the sample by applying either low
pressure or voltage across the capillary; 3) replacing the
inlet buffer reservoir; 4) applying the separation voltage.
After a period of time, the separated sample zones reach
the region of the optical window where spectrophotometric
detection takes lace.
The individual components for injection, separation,
detection, and liquid handling are described in the following
sections. Discussions include the different types of sample
injection and quantitative aspects of injection, capillary
thermostating, high voltage power supply considerations,
and UV-Visible and diode-array detection. Aspects of liquid
handling include buffer replenishment, buffer leveling,
autosampling, and fraction collection. Basic instrument
features designed to simplify method development and
automated analysis are also considered.
4.1 Sample injection
In CE only minute volumes of sample are loaded into the
capillary in order to maintain high efficiency. These small
volumes are, of course, proportional to the small volumes
of the capillaries. With respect to sample overloading, the
injection plug length is a more critical parameter than
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