Assessing caffeine levels in soft beverages available in Istanbul, Turkey: An LC-MS/MS application in food toxicology

Caffeine is most used psychoactive substance as a central nervous system stimulant in the methylxanthine family. The objectives of this research paper was to develop a validated LC-MS/MS assay to measure the caffeine levels in soft beverages (iced tea, ice coffee, and energy drinks) available in Istanbul, Turkey. An analytical assay using LC-MS/MS was conducted, while separation was undertaken using a Shim-Pack FC ODS (150 mm × 2 mm). The validation was carried out in accordance with the ISO/IEC 17025 standard. The linearity was characterized up to 1000 mg/L, using correlation coefficients (r2 = 0.9997) for caffeine. The limit of quantification and limit of detection values of the LC-MS/MS method for caffeine analysis was 0.13 mg/L and 0.04 mg/L, respectively. Demonstrating that the method was accurate, the mean recovery value acquired throughout the spiking experiment was 96.76%, while the relative standard deviation and relative error were equal to 1.68 and 1.75%, respectively. The bias and percent relative standard deviation in caffeine concentration during the inter-day stability testing based on the control chart study were 0.95 and 2.23, respectively. Mean caffeine concentrations in iced tea, energy drinks, and ice coffee were quantified as 37.96 ± 7.46, 105.71 ± 58.48 and 469.10 ± 196.23 mg/L, respectively. Of 13 energy drinks analyzed, two of them exceeded the acceptable caffeine concentration standardized by the Turkish Food Codex. Therefore, toxicological monitoring of caffeine levels in soft beverages should be undertaken with a stricter approach by public authorities.