Figure 2 Electropherogram of 10 nM each (1) dopamine, (2) norepinephrine, and (3) isoproterenol. (Reprinted with permission from Ref. 15.)

An alternative (and very widespread) approach to off-column detection is end-column detection (Figure 1B). In this case, small-diameter fused silica capillaries are employed for the separation. It has been shown by Huang et al. that when capillaries with internal diameters of less than 25 µm are employed, most of the voltage is dropped across the capillary [21]. Therefore, if the electrode is placed just outside the end of the capillary, the separation voltage has minimal influence on the applied detection potential. This obviates the need for a decoupler, making the overall system easier to construct and more rugged because the capillary is made in one piece.