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

as optic cells and GC columns. Similar to GC columns, the
capillaries are coated with a protective layer of polyimide to
make them strong and easy to handle. For detection, an
optical window can easily be placed in the capillary by
removal of a small section of the protective polyimide
coating. This is accomplished by burning off a few millimeters
of polyimide using an electrical arc or electricallyheated
wire, or by scraping with a razor blade. Care must be
exercised when handling a capillary with a window since it
is very brittle after the polyimide is removed.
Teflon is another material used in CE, although not to the
extent of fused silica. Teflon is transparent to UV and thus
requires no special optical window. Although unchanged, it
also exhibits significant EOF. Unfortunately, it is difficult to
obtain with homogeneous inner diameters, exhibits sample
adsorption problems similar to fused silica, and has poor
heat transfer properties. These disadvantages have limited
its use.
Fused silica capillaries with intemal diameters ranging from
10- to 200-µm with a range of outer diameters are available,
however, 25- to 75-µm id and 350- to 400-µm od are typical.
From an analysis time perspective, capillaries as short as
possible should be used. Effective lengths range from as
short as 10 cm for gel-filled capillaries and as long as 80 to
100 cm for complex-sample CZE separations. Most commonly,
50- to 75-cm effective lengths are employed. Ideally
the effective length should be as large a percentage of the
total length as possible in order to be able to apply very
high electric fields and to decrease the time necessary for
capillary conditioning, fraction collection, and so on. The
total length is generally 5 to 15 cm longer, depending on the
dimensions of the instrument (that is, the distance from the
detector to the exit reservoir).
Instrumentation/Operation
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