Spectrophotometric determination of 2-amino-3H-phenoxazin-3-one as a colouring matter in o-aminophenol.

A spectrophotometric method using 0.5M hydrochloric acid in methanol as solvent, has been used for the determination of 2-amino-3H-phenoxazin-3-one [APZ], occurring as a coloured impurity in o-aminophenol [OAP]. This impurity dissolves in the acid medium, giving a stable red solution which complies with Beer's law. The method can be applied to the determination of APZ in technical samples of OAP.