A novel electrochemiluminescent (ECL) reaction between diaminoaromatic ligands and soluble metal ions, specifically reactions between aminoaromatic ligands, such as 2,4-diaminotoluene (2,4,DAT), 3,4-diaminotoluene (3,4,DAT) and 2,3-diaminonaphthalene (2,3-DAN) and metal ions such as Au(I), Cu(II), Cr(VI), Fe(III), Ru)III), Se(IV) and V(V). Such reactions form the basis for ECL assays in detection of various substances, such as the reactants. The ECL interaction between these substances can also form the basis for binding methods in the detection of other substances, such as nucleic acids and antibodies wherein the metal ion ligand ECL complex may be used as a label. The ECL assays are considered useful for carrying out field and laboratory analyses for the detection of TNT breakdown products and toxic metals in wastewater streams, soil, and ground water supplies. In view of the formation of such ECL complexes being dependent on molecular size, further uses are contemplated for measuring atomic size or intermolecular distances of the complexes formed.