Comparison Between Acridan Ester, Luminol, and Ruthenium Chelate Electrochemiluminescence

Transparent indium tin oxide (ITO) electrodes are attractive for use in electrochemiluminescence (ECL). In this work the ECL of an acridan ester (2′,3′,6′-trifluorophenyl 10-methylacridan-9-carboxylate), luminol, and a ruthenium chelate (ruthenium tris 2,2′-bipyridyl) are compared using ITO electrodes. The electrochemistry of all the compounds is described and related to their ECL mechanisms; three possible mechanisms for luminol ECL are described, and it is suggested that the currently accepted mechanism involving luminol and superoxide radicals may not always be correct. Maximum light emission in ruthenium chelate ECL occurs at 1.5 V (vs. Ag/AgCl), but potentials of more than 1 V have a corrosive effect on ITO. The effect of this limitation on ruthenium chelate ECL is discussed as part of a wider assessment of the advantages and disadvantages of ITO as an electrode material for ECL. The effects of pH and H2O2 concentration on ECL detection of the acridan ester and luminol in a planar flow cell are described. The limits of detection of the acridan ester and luminol were 65 pM and 72 pM, respectively.