The method is based on the hydrolysis of a-naphthyl phosphate at pH 5.0 by acid phosphatase (FAC), producing a-naphthol and inorganic phosphate. Pentanediol acts as a phosphate acceptor, increasing the reaction sensitivity. a-naphthol reacts with a diazonium salt, Fast Red TR*, forming a colored complex directly proportional to the FAC activity in the sample.
