An automated HPLC assay for simultaneous quantitation of methylated xanthines and uric acids in urine.

To investigate the elimination kinetics of caffeine and its metabolites, as well as the interaction between them, an automated HPLC method is described. This method involves a single extraction procedure, followed by a gradient elution. Fourteen methylated xanthines and uric acids are well separated with an assay sensitivity of 1 microgram/ml when one-half ml of urine is used. The assay is highly selective, from endogenous compounds, and reproducible. This method is recommended for accurate pharmacokinetic studies.