Studies on simultaneous determination of acetaminophen, salicylic acid and salicyluric acid in biological fluids by high performance liquid chromatography.

A rapid and sensitive high performance liquid chromatographic method was developed for separation and quantitation of acetaminophen, salicylic acid and salicyluric acid in human plasma and urine. The method involved ethyl acetate extraction of the three drugs from plasma or urine followed by evaporation of the organic solvent phase and dissolution of the residue in 100 microliters methanol. A 20 microliters aliquot was analysed on a reversed phase column using an isocratic system of 60 ml/l acetonitrile in 4 mmol/l phosphate buffer, pH 5.7 as a mobile phase and a variable wave length UV detector set at 237 nm. The procedure was used to determine the amounts of the three compounds in plasma and urine of two healthy volunteers who ingested 650 mg of aspirin followed one hour later by 650 mg of acetaminophen.