Temperature control is an important factor in achieving effective and reproducible results in electrophoretic separations, since the properties of the separation medium and the migration characteristics of the solutes both tend to vary when exposed to varying temperatures. Temperature variations occur as a result of the rise in temperature caused by the electrical resistance encountered by the current which drives the solute migration. The temperature rise is more pronounced in systems which utilize a relatively large volume of separation medium. Separations in media which fill slab-shaped and tube-shaped enclosures, for example, are more susceptible than those performed in capillary tubing where heat transfer through the capillary wall is generally sufficient to cool the medium. To avoid or minimize these variations, this temperature rise must be held in check.
In systems where heat transfer to the atmosphere alone does not provide sufficient cooling, one of the buffer solutions used to provide the electrical contact between the separation medium and the electrodes is also used as a heat transfer medium. For the buffer solution to serve both functions, a larger quantity is used than would otherwise be employed, the excess serving as a heat sink. Buffer solution heat sinks are commonly used with slab gels, where the flat faces of the slab gel enclosure provide a convenient contact area for heat transfer. In such arrangements, one or both of the electrode buffers is held in a chamber which not only contains the electrode and encloses one edge of the gel but also extends along the surface of one or both of the glass plates which form one side of the gel enclosure. To distribute the cooling over the entire gel face, the buffer solution is circulated or agitated within the chamber while a small portion of the buffer is refrigerated through a small segment of the chamber wall.
Cooling arrangements of this type are difficult to control, since only a small portion of the buffer solution is actually cooled and uniform mixing is difficult to achieve in the flat chambers which hold the solution against the glass plate. Electronic cooling devices have also been used, but these have been found to be less than fully satisfactory. Conventional approaches to circulating a coolant through a refrigeration system are not applicable to a buffer solution in an electrophoretic system since the buffer solution is electrified and raises a potential electrical hazard in the refrigeration equipment.