Tris(2,2′-bipyridyl)ruthenium(III)-based electrochemiluminescence detector with indium/tin oxide working electrode for capillary electrophoresis

A novel tris(2,2′-bipyridyl)ruthenium(III) [Ru(bpy)33+]-based electrochemiluminescence (ECL) detector for capillary electrophoresis (CE) has been developed. The detector was of the wall-jet configuration and an indium/tin oxide (ITO)-coated glass plate was used as the working electrode for end-column detection. Potential control of the ITO electrode was provided using a DC battery, without decoupling the detector from the CE field. Electrochemical behavior of Ru(bpy)32+ at the ITO electrode was found to be analogous to that at a Pt electrode. In the presence of tertiary or some secondary amines, ECL emission due to reaction between in situ generated Ru(bpy)33+ and analytes can be observed at the ITO surface. With 15 mM sodium borate (pH 9.5) plus 1 mM Ru(bpy)32+ present in the detection cell and the ITO electrode biased at 1.5 V (vs. Pt wire reference), a detection limit of 1 μM proline with a theoretical plate number of 4000 was obtained using the developed CE–ECL detection system. The detector response was found to be analyte-dependent, e.g. tryptophan gives no response, and the response for histidine is about 13-fold lower than that of proline.