Combination of flow injection with capillary electrophoresis: 8. Miniaturized capillary electrophoresis system with flow injection sample introduction and electrogenerated chemiluminescence detection

The combined flow injection (FI)-capillary electrophoresis (CE) system was further exploited by coupling to an electrogenerated chemiluminescence (ECL) detection system. A low-cost miniaturized CE system was developed on a chip platform to provide easy interface both with FI sample introduction and with ECL detection. A falling-drop interface was employed to perform FI split-flow sample introduction while achieving electrical isolation from the CE high voltage. A plexiglas reservoir at the capillary outlet served as both the reaction and detection cell for the ECL reaction, with Ru(bpy)₃²⁺ reagent continuously flowing through the cell. An optical fiber was positioned within the reservoir close to the capillary outlet for transferring the ECL emission to the PMT. The relative positions of the capillary outlet, working electrode and optical fiber as well as reagent renewal flow-rate were optimized to achieve both good sensitivity and separation efficiency under non-interrupted sampling conditions, involving large numbers of samples. An on-column joint often used in other works for isolating the ECL detection system from the CE separation voltage was not found necessary. The performance of the system was illustrated by the baseline separation of proline, valine and phenylalanine with a high throughput of 50 h⁻¹ and plate height of 14 μm for proline under 147 V cm⁻¹ field strength. Detection limits (3σ) were 1.2, 50 and 25 μM and peak height precisions were 1.4, 5.4 and 4.3% R.S.D. (n=9) for proline, valine and phenylalanine, respectively.