Large-volume sample sweeping with a high theoretical plate number using a coupled-capillary in capillary electrophoresis.

A large-volume sample injection (> 5 microL) with an extremely high theoretical plate number (N > 10(7)) was achieved when the sweeping-MEKC mode and a coupled-capillary (100 - 50 microm i.d.) were simultaneously used in a capillary electrophoresis (CE) separation. A low-cost and compact violet-LED ( approximately 2 mW) was used as the fluorescence excitation source. As a result, the theoretical plate numbers of the detected peaks (two model compounds: naphthalene-2,3-dicarboxaldehyde derivatized-dopamine and -norepinephrine) were 1.0 x 10(7) and 7.4 x 10(6), respectively. The limits of detection (at S/N = 3) of these were determined to be 2.8 x 10(-10) M (92 ppt) and 2.3 x 10(-10) M (83 ppt), respectively.