Page 502 - Tandem Techniques

Page 488

Another method of solute concentration was introduced by Thompson et al., [7], who employed an
isotachophoretic procedure for preconcentrating the sample before separation by capillary
electrophoresis. The different types of ionic separation techniques are described at the end of Chapter 1,
and it is recalled that in isotachophoresis, there is a leading and terminating electrolyte. On application
of the driving potential, the solutes line up between the two electrolytes according to their individual
ionic mobilities. The system is self-focusing, and if some ions disperse away from their equilibrium
position, they will suffer differential forces that cause them to move back to their respective ionic
mobility position. Consequently, if the sample is dilute, each solute will be compressed between the
leading and terminating electrolytes and will be concentrated.

The arrangement of the apparatus used by Thompson et al. is depicted in Figure 13.3.

Figure 13. 3
The Capillary Electrophoresis Electrospray Interface

The electrophoretic system comprised a power supply, a fused silica separating capillary, and an anode
reservoir. The capillary could be used, separately or sequentially, both for isotachophoretic
concentration and for electrophoretic separation. The separated components were driven under