Background-correction methods for the determination of caffeine in beverages, coffee and tea by using second-derivative ultraviolet spectrophotometry

Abstract

Background-correction methods have been developed for the determination of caffeine in beverages, coffee and tea by second-derivative ultraviolet spectrophotometry. The second derivatives of caffeine were measured at 298.6 nm. Interference from tannins in beverages and tea was minimized by treating the sample with 0.1 mol dm^–3 sodium hydroxide and by precipitating tannins with copper(II) acetate, respectively. Coffee samples were treated with sodium hydroxide (0.25–0.75 mmol dm^–3). The calibration graphs for the three types of sample had slightly different slopes (0.00146–0.00152 A nm^–2 ppm^–1) and linear ranges. The precision for the determination ranged from 0.3 to 0.9%, at the 10 µg ml^–1 level of caffeine. A number of cola drinks, energy drinks, lemon tea drinks, coffee samples and tea samples were analysed.