In chemistry, a carbazide is a functional group with the general formula RNH-NH(C=O)NH-NHR.
[1] Diphenylcarbazide forms an intense blue color with chromium in the hexavalent state.
That means very small amounts of chromium can be detected; 25 micrograms in 25 mL of solution are too dark to read on a spectral device, so concentrations well below that can be detected.
The sulfur analog is called a thiocarbazide, of which thiocarbohydrazide is the simplest example.
A carbazone is a partially oxidized carbazide with the general formula R=NNH(C=O)NH-NHR.