Simultaneous quantification of caffeine and its three primary metabolites in rat plasma by liquid chromatography–tandem mass spectrometry

Abstract

A rapid, sensitive, simple and accurate LC–MS/MS method for the simultaneous quantitation of caffeine, and its three primary metabolites, theobromine, paraxanthine, and theophylline, in rat plasma was developed and validated. Chromatographic separation was performed on an Agilent Poroshell 120 EC-C18 column using 1μg/mL acetaminophen as an internal standard. Each sample was run at 0.5mL/min for a total run time of 7min/sample. Detection and quantification were performed using a mass spectrometer in selected reaction-monitoring mode with positive electrospray ionization. The lower limit of quantification was 5ng/mL for all analytes with linear ranges up to 5000ng/mL for caffeine and 1000ng/mL for its metabolites. The coefficient of variation for assay precision was less than 12.6%, with an accuracy of 93.5–114%. The assay was successfully applied to determine plasma concentrations of caffeine, theobromine, paraxanthine, and theophylline in rat administered various energy drinks containing the same caffeine content. Various energy drinks exhibited considerable variability in the pharmacokinetic profiles of caffeine and its three primary metabolites, even containing the same caffeine. Different additives of energy drinks might contribute to these results.