Rapid colorimetric assay for acetaminophen without salicylate or phenylephrine interference.

A simple rapid, and economical procedure is presented for the quantitative determination of acetaminophen in serum. Acetaminophen is extracted into solvent, and, when back-extracted into base, is simultaneously reacted with Folin-Ciocalteau reagent to form a colored complex. The potential interference of bilirubin is eliminated by treatment with p-diazobenzene sulfonic acid. Results obtained with this method agree with those obtained by "high-pressure" liquid chromatography.