Simultaneous measurements of acetaminophen and salicylate in plasma by liquid chromatography.

We describe a "highly-performance" liquid chromatographic method in which 8-chlorotheophylline is used as an internal standard to determine acetaminophen and salicylate simultaneously in plasma samples. Therapeutic as well as toxic concentrations can be determined on samples as small as 50 micro L, which makes the method particularly useful for determinations on samples from young children. The procedure requires a simple extraction of the drugs, and the chromatography is completed in 6 min.