Diphenylcarbazide oxidizes to Diphenylcarbazone when exposed to light and air, turning pink in the process.

Diphenylcarbazide is used as a redox indicator[3] and for the photometric determination of certain heavy metal ions, like those of Chromium, Mercury, Cadmium, Osmium, Rubidium, Technetium and more.

Diphenylcarbazide has also been widely used in the chemical lab to detect Mercury (II) compounds, in a similar fashion.

The reagent is typically used either as 1% to 0.25% solution in some organic solvent, or in the form of test-strip paper for detection of heavy metals in drinking water at home.

Aqueous solutions and solvents tending to be basic such as methanol and ethanol, and those containing traces of water and basic impurities, do not make good solvents for stock solutions of the colorimetric reagent[10] At least 16 different routes to synthesizing the compound are known, most of which use Phenylhydrazine.