Highly sensitive chelating agents for histochemical staining of rare earth metals

In tissues, bromopyridylazo-diethylaminophenol has been found to be capable of staining very small amounts of rare earth metals, particularly praseodymium, terbium, dysprosium, holmium, ytterbium, and lutetium. Differentiation of a target metal from interfering metals was achieved using masking agents, polyphosphates and aminopolycarboxylic acids.