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

The simplest way to perform a stacking experiment is to
dissolve the sample in water or low conductivity buffer (for
example, 100 to 1000 times lower than that of the running
buffer) and inject normally either hydrodynamically or
electrokinetically. Stacking will occur automatically. More
than a 10-fold sample enrichment can be obtained (figure
53). If the conductivity of the sample and running buffer are
equivalent, stacking can be induced by injecting a short plug
of water before sample introduction.
a)
A
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A
B
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Instrumentation/Operation
b) B
C
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A
B
Figure 53
Field amplified sample injection 29
a) sample dissolved in buffer
b) sample dissolved in water
c) short plug of water injected before
sample in (b)
c)
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Time [min]
C
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Other stacking methods have been described in which up
to 50 % of the capillary can be filled with sample, the buffer
removed by the EOF, and the sample stacked in a small
zone at the head of the capillary (called field amplified
injection). Effective use of these methods is limited, however,
by the electro-osmotic pressure developed at the
boundary between the water and buffer zones. This pressure
difference causes generation of laminar flow and
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