Use of 3-(1,8-naphthalimido)propyl-modified silyl silica gel as a stationary phase for the high-performance liquid chromatographic separation of purine derivatives.

The use of a packing material, 3-(1,8-naphthalimido)propyl-modified silyl silica gel (NAIP), as a stationary phase for high-performance liquid chromatography, has been studied. NAIP behaved like a reversed-phase stationary phase with some pi-pi interaction. Purine derivatives, i.e., xanthine, hypoxanthine, uric acid, theobromine, theophylline and caffeine, were separated by a column packed with NAIP using an eluent of borate solution (pH 6.4)-MeOH (50:50, v/v). Of these, caffeine was selected as the target of the subsequent investigation and its determination was examined in commercially available medicinal drinks and pharmaceutical preparations. The average recoveries of caffeine were 98.0-107.4% for five drinks and 99.6-107.8% for five tablets and one powder. Subsequently, determination of caffeine and its metabolites in human plasma was examined. In twelve normal human plasma, caffeine levels ranged from 0.24 to 4.26 micrograms/ml. Time curves of plasma caffeine concentrations and those of its demethylated metabolite, 1,7-dimethylxanthine (1,7-DMX), after an oral ingestion of caffeine (200 mg) were measured by the proposed method and it was found that the maximum concentrations of caffeine and 1,7-DMX were obtained at 1-1.5 h and 3-6 h after ingestion, respectively.