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

Principles
Note that equation (15) should only be used for Gaussian
peaks. Any asymmetry should be taken into account, for
example, by use of central moments.
In practice, the measured efficiency, equation (15), is usually
lower than the calculated efficiency, equation (14). This is
because the theoretical calculation accounts only for zone
broadening due to longitudinal diffusion. As described in the
next section, other dispersive processes are often present.
2.3.4.1 Factors affecting efficiency
Dispersion in CE can have a number of contributors in
addition to longitudinal diffusion. Among the most important
are temperature gradients induced by Joule heating, injection
plug length, and solute interactions with the capillary walls.
Fortunately, these phenomena are usually controllable, as
discussed below. These and other zone broadening mechanisms
are described in table 3.
Dispersion, as described by equation (13), was derived with
the assumption that the only contributor was molecular
diffusion. The variance is better described by the total
variance of the system, s 2 , which is given by the sum of the
T
contributing variances
s 2 = T s2 + DIF s2 + INJ s2 + TEMP s2 + ADS s2 + DET s2 +...
Electrodispersion
(16)
where the subscripts refer to diffusion, injection, temperature
gradients, adsorption, detection, and electrodispersion,
respectively. If any of the dispersion processes in equation
(16) dominate the diffusion term, theoretical limits cannot
be obtained and equation (14) will not be valid. In this case,
only minimal improvements in efficiency and resolution can
be obtained by increased voltage.
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