Revised Assay for Serum Phenyl Phosphatase Activity Using 4- Amino - Antipyrine

A modified method for the assay of serum phosphatase activity utilising disodium phenyl phosphate as substrate is described. This is based upon the reaction of free phenol with 4-amino-antipyrine and alkaline potassium ferricyanide. Study of the kinetics of the colour reaction has led to an alteration in the concentration of the reagents used; the colour is formed instantaneously and shows a very slow rate of decay. Sodium arsenate incorporated with the amino-antipyrine reagent effectively abolishes further enzyme activity and prevents the dilution of the colour inherent in earlier methods.