Cupferron

Cupferron is jargon for the ammonium salt of the conjugate base derived from N-nitroso-N-phenylhydroxylamine. It once was a common reagent for the complexation of metal ions, being of interest in the area of qualitative inorganic analysis. Its formula is NH4[C6H5N(O)NO]. The anion binds to metal cations through the two oxygen atoms, forming five-membered chelate rings.