The multiplicity of the interaction products of FeCl3 and KI are adequate to detect drugs bearing a nitrogen group, bases, imides, purines, in particular. To take advantage of the chemical ability of the two constituents of the reagent singularly they are applied to the plate in sequence. FeCl3 will act as a positive ion Fe+3 and it will chealate, oxidate, and produce salts. KI by reacting with FeCl3 will produce a new chemical specie, for example, Fe(Cl3I3)6(-3), Werner complexes, and production of elemental iodine that further interacts with KI and drugs facilitating detection with adequate sensitivity and for practical use.