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

Instrumentation/Operation
the capability of random access to the vials. In either case,
it is important that the anodic and cathodic reservoirs
contain the same buffer composition. Differences in the
reservoir contents can result in absorbance fluctuations,
current changes, and variations in EOF.
Cooling of the autosampler is required if thermally labile
samples are used. Thermostating is also beneficial in
reducing sample evaporation which can increase sample
concentration and limit quantitative analysis. Similarly,
tightly capped sample vials also limit evaporation.
4.4.2 Fraction collector
Although minute quantities are injected into an CE system,
fraction collection is often desirable. While only picogram
quantities of material are usually collected, this may be
sufficient for a number of further analyses, including reinjection
with different running buffers or using different
CE modes, or sequencing, mass spectrometry or enzymatic
assay. If sufficient material is not obtained, multiple collections
can easily be automated.
Elution of the solute into the collection vial may best be
accomplished by pressure since the solute may migrate to
the electrode and adsorb or react. This is especially relevant
when the collection vial contains water or other low conductivity
medium. As described for the autosampler, cooling of
the fraction collector is desirable.
Collection of narrow, closely spaced peaks can be simplified
by voltage programming. As previously described, reduction
of the field immediately prior to collection increases the
time-window and relaxes the stringent timing problems
associated with precise collection. This is illustrated in
figure 66.
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