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

Source
Longitudinal diffusion
Joule heating
Comment
• Defines the fundamental limit of efficiency
• Solutes with lower diffusion coefficients
form narrower zones
• Leads to temperature gradients and
laminar flow
Principles
Table 3
Sources of zone broadening
Injection length
Sample adsorption
Mismatched conductivities
of sample and buffer
(electrodispersion)
Unlevel buffer reservoirs
Detector cell size
• Injection lengths should be less than the
diffusion-controlled zone length
• Detection limit difficulties often necessitate
longer than ideal injection lengths
• Interaction of solute with the capillary walls
usually causes severe peak tailing
• Solutes with higher conductivities than the
running buffer result in fronted peaks
• Solutes with lower conductivities than the
running buffer result in tailed peaks
• Generates laminar flow
• Should be small relative to peak width
2.3.4.2 Joule heating and temperature gradients
The main advantage of performing electrophoresis in
narrow-bore capillaries is reduction of the effects of heating
which have traditionally limited electrophoretic techniques.
Heating is problematic since it can cause nonuniform
temperature gradients, local changes in viscosity, and
subsequent zone broadening. While the theoretical equations
for efficiency and resolution advocate the use of as
high electric fields as possible, Joule heating ultimately
limits the benefit of this approach, regardless of capillary
dimensions and temperature control measures.
The heat generated by the passage of electrical current is
called Joule heat. The temperature increase depends on the
power (product of voltage and current) generated and is
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