Determination of theophylline and its metabolites in plasma and urine by reversed-phase liquid chromatography using an amine modifier.

A high-performance liquid chromatographic method for the determination of the concentrations of theophylline and its metabolites in plasma and urine samples is presented. The method uses the decylammonium ion, an N-alkylammonium modifier, and makes it possible to separate theophylline and its metabolites from other uric acid or xanthine derivatives, especially 1,7-dimethylxanthine, a metabolite of caffeine. The plasma and urine purification procedure is convenient, rapid and reproducible, and it can be used to determine low plasma and urine concentrations.