Murexide, the ammonium salt of purpuric acid, is extensively used as a ligand to form complexes with many metal ions. For example, it is used as the indicator for EDTA titration of Co(ll). The decomposition of murexide to form uramil and alloxan in acid solution can be followed spectrophotometrically at 523nm.
The rate of decompositon is dependent on the pH of the solution. At a fixed (i.e. constant) pH,the decomposition of murexide is a first order reaction.