A novel assay for the determination of 2,4- and 3,4-diaminotoluene (DAT) isomers based on the low-level electrochemiluminescence (ECL) reaction of these molecules with the group IB transition metal ions Au+and Cu+2, respectively, in aqueous solution is described. DAT isomers were screened for ECL against a repertoire of 32 metals, including metal ions such as Cu+2, Eu+3, Mg+2, Ru+3, and Tb+3associated with other known ECL complexes, at 1:3 added metal ion:ligand molar ratios. The 1:3 molar ratio presumed tris-bidentate octahedral metal coordination complex formation, which generally yielded optimal ECL intensity. The apparent specificity of Au+for 2,4-DAT and Cu+2for 3,4-DAT, as indicated by ECL measurements, may be partly based on ionic size as Au+has nearly twice the ionic diameter of Cu+2and thus may form a coordination complex with themeta,but not theorthoDAT. Other DAT isomers were screened and exhibited mildly enhanced ECL with various metal ions, including group IB transition metal ions, but these ECL enhancements were not statistically significant. In some cases, titration of DAT ligands with Cu+2and Au+over broad concentration ranges produced nonlinear ECL response curves. Despite low-level ECL, sensitivities in the ppm range for Au+, Cu+2, and their respective DAT isomers were achieved. Time dependence was observed for some of the ECL reactions, including the Ru(III)–bipyridine model system, in which the ECL intensity grew markedly over several hours. No ECL enhancements over background were observed with two dinitrotoluene isomers or an aminonitrotoluene screened against the same set of 32 metals. This novel ECL approach may have applications in the determination of some aminoaromatics from degradation of explosives (e.g., TNT) as well as detection and quantitation of various transition metals in industrial wastewater streams and groundwater supplies. In terms of fundamental science, the present data are probably of interest as an example of size-dependent molecular recognition of metal ions which can be detected by ECL.