Rapid spectrophotometric method for the quantitation of acetaminophen in serum

A novel spectrophotometric method for rapid quantification of acetaminophen in serum is described. Free unconjugated acetaminophen is separated from other endogenous interferents by extracting the drug into ethyl acetate and hydrolysis to p-aminophenol by treatment with heat and acid. The latter compound is capable of undergoing an oxidative coupling reaction with p-xylenol (2,5-dimethylphenol) catalyzed by sodium periodate. The resultant indophenol derivative formed is measured spectrophotometrically at 635nm. The proposed method has a linearity range from 25 to 600µgml-1. The method was precise with day-to-day coefficients of variation for two controls (101 and 204µgml-1) of 4.8 and 7.0%, respectively. A group of commonly used prescription drugs or compounds likely to be potential interferents on the basis of their chemical structures were tested and found not to interfere. Results obtained by the proposed method correlated excellently with those determined by either the nitration or the direct acid iron(III) redox methods with correlation coefficients of 0.97 and 0.98, respectively. The proposed method for acetaminophen determination is simple and rapid and is especially suitable for screening for drug overdose in an emergency situation.