Abstract:This study established a method for the determination of caffeine in tea-drinks using microemulsion ultra-high performance liquid chromatography and investigated the effects of the composition and pH value of the microemulsion mobile phase. The samples only required simple dilution and filtration through a 0.22 μm microporous membrane before direct injection. A Waters BEH C18 column （2.1 μm×150 mm， 1.7 μm） was used， and the mobile phase consisted of an aqueous solution of 9.3 g/L sodium dodecyl sulfate， 60 g/L n-butanol， 8 g/L n-heptane， 0.4 g/L phosphoric acid， and 3.4 g/L potassium dihydrogen phosphate. The flow rate was 0.20 mL/min， the detection wavelength was 272 nm， and the column temperature was maintained at 30 ℃. Quantitative analysis was performed using the external standard method. Under the selected experimental conditions， caffeine showed a good linear relationship in the concentration range of 0.5-20.0 mg/L （r =0.999）， with a detection limit of 0.005 g/kg. The recovery of caffeine ranged from 88.0% to 101.0%. The sample was measured repeatedly six times， and the relative standard deviations of the peak areas were all less than 5%， indicating that the method can be used for the determination of caffeine in tea-drinks.