Application of Diamond Microelectrodes for End-Column Electrochemical Detection in Capillary Electrophoresis

Highly boron-doped diamond microelectrodes were employed in an end-column electrochemical detector for capillary electrophoresis (CE). The diamond microline electrodes were fabricated from conducting diamond thin films (exposed surface area, 300 × 50 μm), and their analytical performance as CE detectors was evaluated in a laboratory-made CE installation. The CE-ED system exhibited high separation efficiency for the detection of several catecholamines, including dopamine (DA), norepinephrine (NE), and epinephrine (E), with excellent analytical performance, for example, 155 000 theoretical plates for DA. The diamond-based electrochemical detection system also displayed low detection limits (∼20 nM for E at S/N = 3) and a highly reproducible current response with 10 repetitive injections of mixed analytes containing DA, NE, and E (each 50 μM), with relative standard deviations (RSD) of ∼5%. The performance of the diamond detector in CE was also evaluated in the detection of chlorinated phenols (CP). When compared to the carbon fiber microelectrode, the diamond electrode exhibited lower detection limits in an end-column CE detection resulting from very low noise levels and highly reproducible analyses without electrode polishing due to analyte fouling, which makes it possible to perform easier and more stable CE analysis.