ABSTRACT
After giving a survey of the literature of the HPLC methods for the determination of caffeine, theophylline and theobromine two methods are presented for their purity test, i.e. their detection in each other at the trace level. In the reversed-phase system the stationary phase was C18-silica and the 2:3 mixture of methanol and water was used as the eluent at a detection wavelength of 254 nm. The k' values for theobromine, theophylline and caffeine are 0,25, 0,62 and 1,12, respectively. This system enables the detection of 0,2% of theobromine and 0,1% of theophylline in caffeine and 0,2% of caffeine in theobromine or theophylline. In the normal phase system silica was used as the stationary phase while the eluent was 85:15:0,05 mixture of chloroform, dioxane and formic acid. The wavelength of the detection was 273 nm. The k' values of caffeine, theobromine and theophylline are 1,5 4,0 and 5,6, respectively. This system also enables the detection of 0,1% of theophylline and theobromine in caffeine or 0,2% of caffeine in the former. Theophyline and theobromine can be detected in each other at the 0,1% level.