Derivative spectrophotometric assay of acetaminophen and spectrofluorimetric determination of its main impurity

Abstract Second derivative UV spectrophotometry proved to be a useful tool for the determination of acetaminophen, even in the presence of high amounts of the impurity, 4-aminophenol and the background effect caused by dissolved excipients of some dosage forms. The fluorimetric method used for the estimation of 4-aminophenol impurity is less sensitive than the colorimetric methods used in the pharmacopeias. This can be attributed to an inner-filter effect.