Centrifugal extraction procedure for the ultraviolet spectrophotometric determination of caffeine in beverages

A rapid, accurate and organic solvent saving method has been developed for the ultraviolet spectrophotometric (UV) determination of caffeine in beverages. The centrifugal extraction procedure with large phase ratio was applied to sample micropreparation prior to instrumental analysis. The method involves the mixing of 100 mu L sample with 2 mL chloroform and a 3-min centrifugal extraction procedure in a centrifugal tube. The clear solution obtained was directly determined by UV detection at wavelength of 278 nm. The manipulation was simple and repeatable, and the relative standard deviation of the method was less than 3% for the independent measurement. When added different concentration of standard caffeine solution to three brand beverages, the recovery of the caffeine was in the range of 96.6% - 106.1%. A linear calibration curve was obtained with caffeine concentration ranging from 0.50 - 30 mg/L, giving the correlation coefficient as 0.9999. The method provides a 0.001 mg/L detection limit of caffeine. The developed method was applied to determine the caffeine content in commercial beverages with good results.