Simultaneous Spectrophotometric Determination of Diphenylhydantoin and Phenobarbital in Biologic Specimens

Abstract

A rapid, accurate method for determining diphenylhydantoin and phenobarbital in a single biologic sample is described. Separation of the two drugs after their initial chloroform extraction from the specimen is not required. After extraction, diphenylhydantoin is converted to benzophenone by pemanganate oxidation. Phenobarbital is determined by differential absorption between pH values of 12.0 and 10.5. Final quantitation in each case is carried out by ultraviolet spectrophotometry. Barbiturates do not interfere with the diphenylhydantoin analysis or vice versa. The method is sensitive enough for detecting subtherapeutic amounts of each compound with a high degree of specificity.