Combination of flow injection with capillary electrophoresis: Part 7. Microchip capillary electrophoresis system with flow injection sample introduction and amperometric detection

Abstract

A microchip-based capillary electrophoresis (CE) system with amperometric detection, combined with flow injection (FI) sample introduction, was constructed from components readily available in the analytical laboratory. An H-channel configuration was used with separation capillary positioned between two tubular side-arms, and a falling-drop interface connected to one side-arm was developed to achieve electrical isolation between the FI and CE systems. End-column amperometric detection was accomplished with separation voltage decoupled from the detection system, employing a microdisk working electrode positioned immediately outside the capillary outlet in the other side-arm, which functioned as a large-volume reservoir. Sample dispersion in the FI system and the FI–CE interface was minimized by intercalating the sample zone between two air segments. Performance of the FI–CE amperometric system was demonstrated by separation of sugars. Separation of sucrose and glucose was performed with a 5 cm, 25 μm i.d. capillary with 1.7 kV separation voltage in about 60 s (40 μm plate height for glucose), achieving a sampling frequency of over 65 h −1. Responses for sucrose and glucose were linear in the range of 10–1000 μM with sensitivities of 0.011 and 0.025 nA μM −1. Detection limits ( S/ N=3) were 2 μM for sucrose and 1 μM for glucose. Peak height precisions were 2.1 and 2.4% R.S.D. ( n=9) for sucrose and glucose, respectively.