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

Temperature
Principles
Capillary
wall
Capillary
center
Capillary
wall
Polyimide
coating
Surrounding
environment
Surrounding
environment
Figure 13
Schematic of temperature gradients from
capillary center to the surroundings
390 375 25 0 25
375 390
d [µm]
An example of the calculated temperature difference between
the internal capillary wall and the capillary center is
given in table 4.
Radius (µm) Wall temperature, K Temperature difference, K
Table 4
Capillary wall temperature and center-towall
temperature difference 5
25 299.0 0.53
50 301.2 1.39
75 304.2 3.14
100 307.7 5.58
125 311.6 8.72
Equation (17) implies that it is advantageous to use narrow
inner radii capillaries with large outer radii. As mentioned,
the small volume limits the quantity of heat generated, even
when several hundred volts per centimeter are applied. In
addition, the high inner surface-to-volume ratio helps
dissipate the generated heat through the capillary wall. The
large outer diameter is advantageous due to a reduction in
the insulating properties of the polyimide and improvement
of heat transfer to the surroundings. Although the polyimide
coating is only a few microns thick, its low thermal conductivity
significantly limits heat transfer.
There are a number of methods that indicate excessive
heat generation and possible temperature gradients. These
phenomena may be indicated if efficiency is reduced as the
33