Fluorometric reactions of purines and determination of caffeine.

Two new spot-tests for purines are described together with a new sensitive determination of caffeine. The spot tests involve a fluorometric reaction with 4,5-dimethyl-o-phenylenediamine after oxidation with N-bromosuccinimide. Caffeine treated in this manner exhibits a blue fluorescence with excitation maxima at 340 and 390 nm, and an emission maximum at 480 nm. The fluorometric reaction may be used to determine caffeine in the range 0.01-10, mug/ml with a relative standard deviation of 0.9% for 0.1 mug/ml caffeine. The method has been used to determine caffeine in cough syrups.