Temperature profile of buffer-filled electrophoresis capillaries using air convection cooling

Temperature profiles of buffer-filled capillaries (capillary temperature), using both natural and forced air convection for cooling, were obtained both theoretically and experimentally in order to achieve stable capillary electrophoresis for accurate DNA sequencing analysis. The capillary temperature was calculated using the temperature dependency of the buffer resistivity, and the threshold values of the electric field and the capillary temperature for temperature instability were characterized. The capillary temperature became unstable at about 420 V/cm and at about 62 degrees C regardless of the outer diameter of the capillary; these values approximately coincide with the measured values obtained using a very thin thermocouple. The sets of values of electric field, air temperature, and air flow velocity in forced air cooling were obtained to keep the capillary temperature at the 40-60 degrees C needed for accurate DNA sequencing in a Tris-boric acid-EDTA buffer.