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Two ion chromatographic methods have been proposed for the simultaneous determination of caffeine, theobromine and theophylline. The separations were based on isocratic elutions and the determinations on ultraviolet absorbance detections at 274 nm. The detection limits (signal-to-noise ratio 3:1) for the three compounds were all below sub-mg ml À1 level. The methods have been successfully applied to the determination of these three compounds in foods and pharmaceutical preparations, and the average recoveries for various samples ranged from 87% to 103%. In addition, the retention mechanisms of these three compounds on various ion-exchange resins were discussed. The results obtained revealed that ion-exchange chromatography is possibly a good alternative to conventional liquid chromatography for the separation and determination of some water-soluble, neutral organic molecules with a certain hydrophobicity. #

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