Simultaneous determination of caffeine, theophylline and theobromine in food samples by a kinetic spectrophotometric method.

A novel kinetic spectrophotometric method was developed for the simultaneous determination of caffeine, theobromine and theophylline in food samples. This method was based on the different kinetic characteristics between the reactions of analytes with cerium sulphate in sulphuric acid and the associated change in absorbance at 320 nm. Experimental conditions, the effects of sulphuric acid, cerium sulphate and temperature, were optimised. Linear ranges (0.4-8.4 μg mL(-1)) for all three analytes were established, and the limits of detection were: 0.30 μg mL(-1) (caffeine), 0.33 μg mL(-1) (theobromine) and 0.16 μg mL(-1) (theophylline). The recorded data were processed by partial least squares and artificial neural network, and the developed mathematical models were then used for prediction. The proposed, novel method was applied to determine the analytes in commercial food samples, and there were no significant differences between the results from the proposed method and those obtained by high-performance liquid chromatography.