Determination of N-Acetyl-p-Aminophenol in Plasma

Two methods for the determination of N-acetyl-p-aminophenol (APAP) in plasma that differ in principle from the diazotization procedure of Brodie and Axelrod (1) are described. One method based on the differential absorption peak of APAP at 266 mµ, which corresponds to the isosbestic point of common drugs such as acetylsalicylic and salicylic acids, is simple and most specific for APAP. The other method employs a free-radical dye diphenylpicrylhydrazyl which extracts a hydrogen atom from the APAP molecule and is progressively decolorized. The dye method is the least complex and most sensitive. All three methods exhibited satisfactory replication, recovery of added APAP, and comparable plasma levels of the drug.