Caffeine content of energy drinks, carbonated sodas, and other beverages.

The caffeine content of 10 energy drinks, 19 carbonated sodas, and 7 other beverages was determined. In addition, the variability of the caffeine content of Coca-Cola fountain soda was evaluated. Caffeine was isolated from the samples by liquid-liquid extraction and analyzed by gas chromatography with nitrogen-phosphorus detection. The caffeine concentration of the caffeinated energy drinks ranged from none detected to 141.1 mg/serving. The caffeine content of the carbonated sodas ranged from none detected to 48.2 mg/serving, and the content of the other beverages ranged from < 2.7 to 105.7 mg/serving. The intra-assay mean, standard deviation, and % coefficient of variation for the Coca-Cola fountain samples were 44.5, 2.95, and 6.64 mg/serving, respectively.