Colorimetric assay for acetaminophen in serum

A colorimetric method for determination of acetaminophen in serum, based on its reaction with 2-nitroso-1-naphthol-4-sulfonic acid, is described. The method is sensitive, rapid, and free from the interferences of serum matrix and most common drugs. The method can be performed manually or can be semiautomated. The results from this method correlate well with values determined by high-performance liquid chromatography.