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

Principles
Total length
Effective length
Detector
detection (mass spectrometry, for example), the two lengths
are equivalent. Knowledge of both lengths is important since
the migration time and mobility are defined by the effective
length, whereas the electric field is defined by the total
length.
2.3.4 Dispersion
Inlet
reservoir
Exit
reservoir
Figure 11
Definition of effective and total capillary
lengths
Separation in electrophoresis is based on differences in
solute mobility. The difference necessary to resolve two
zones is dependent on the length of the zones. Zone length is
strongly dependent on the dispersive processes that act on
it. Dispersion should be controlled because it increases zone
length and the mobility difference necessary to achieve
separation.
Dispersion, spreading of the solute zone, results from
differences in solute velocity within that zone, and can be
defined as the baseline peak width, w b
. For a Gaussian peak,
w b
= 4 s (10)
where
s = standard deviation of the peak
(in time, length, or volume).
The efficiency, expressed in number of theoretical plates, N,
can be obtained by
2
l
N = (11)
( s )
where 1 = capillary effective length
and can be related to the HETP (height equivalent to a
theoretical plate), H, by
( )
l
H = (12)
N
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